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Influenza

Influenza

Definition

Usually referred to as the flu or grippe, influenza is a highly infectious respiratory disease. The disease is caused by certain strains of the influenza virus. When the virus is inhaled, it attacks cells in the upper respiratory tract, causing typical flu symptoms such as fatigue, fever and chills, a hacking cough, and body aches. Influenza victims are also susceptible to potentially life-threatening secondary infections. Although the stomach or intestinal "flu" is commonly blamed for stomach upsets and diarrhea, the influenza virus rarely causes gastrointestinal symptoms. Such symptoms are most likely due to other organisms such as rotavirus, Salmonella, Shigella, or Escherichia coli.

Description

The flu is considerably more debilitating than the common cold. Influenza outbreaks occur suddenly, and infection spreads rapidly. The annual death toll attributable to influenza and its complications averages 20,000 in the United States alone. In the 19181919 Spanish flu pandemic, the death toll reached a staggering 20-40 million worldwide. Approximately 500,000 of these fatalities occurred in America.

Influenza outbreaks occur on a regular basis. The most serious outbreaks are pandemics, which affect millions of people worldwide and last for several months. The 19181919 influenza outbreak serves as the primary example of an influenza pandemic. Pandemics also occurred in 1957 and 1968 with the Asian flu and Hong Kong flu, respectively. The Asian flu was responsible for 70,000 deaths in the United States, while the Hong Kong flu killed 34,000.

Epidemics are widespread regional outbreaks that occur every two to three years and affect 5-10% of the population. The Russian flu in the winter of 1977 is an example of an epidemic. A regional epidemic is shorter lived than a pandemic, lasting only several weeks. Finally, there are smaller outbreaks each winter that are confined to specific locales.

The earliest existing descriptions of influenza were written nearly 2500 years ago by the ancient Greek physician Hippocrates. Historically, influenza was ascribed to a number of different agents, including "bad air" and several different bacteria. In fact, its name comes from the Italian word for "influence," because people in eighteenth-century Europe thought that the disease was caused by the influence of bad weather. It was not until 1933 that the causative agent was identified as a virus.

There are three types of influenza viruses, identified as A, B, and C. Influenza A can infect a range of animal species, including humans, pigs, horses, and birds, but only humans are infected by types B and C. Influenza A is responsible for most flu cases, while infection with types B and C virus are less common and cause a milder illness.

In the United States, 90% of all deaths from influenza occur among persons older than 65. Flu-related deaths have increased substantially in the United States since the 1970s, largely because of the aging of the American population. In addition, elderly persons are vulnerable because they are often reluctant to be vaccinated against flu.

A new concern regarding influenza is the possibility that hostile groups or governments could use the virus as an agent of bioterrorism. A report published in early 2003 noted that Type A influenza virus has a high potential for use as such an agent because of the virulence of the Type A strain that broke out in Hong Kong in 1997 and the development of laboratory methods for generating large quantities of the virus. The report recommended the stockpiling of present antiviral drugs and speeding up the development of new ones.

Causes and symptoms

Approximately one to four days after infection with the influenza virus, the victim is hit with an array of symptoms. "Hit" is an appropriate term, because symptoms are sudden, harsh, and unmistakable. Typical influenza symptoms include the abrupt onset of a headache, dry cough, and chills, rapidly followed by overall achiness and a fever that may run as high as 104°F (40°C). As the fever subsides, nasal congestion and a sore throat become noticeable. Flu victims feel extremely tired and weak and may not return to their normal energy levels for several days or even a couple of weeks.

Influenza complications usually arise from bacterial infections of the lower respiratory tract. Signs of a secondary respiratory infection often appear just as the victim seems to be recovering. These signs include high fever, intense chills, chest pains associated with breathing, and a productive cough with thick yellowish green sputum. If these symptoms appear, medical treatment is necessary. Other secondary infections, such as sinus or ear infections, may also require medical intervention. Heart and lung problems, and other chronic diseases, can be aggravated by influenza, which is a particular concern with elderly patients.

With children and teenagers, it is advisable to be alert for symptoms of Reye's syndrome, a rare, but serious complication. Symptoms of Reye's syndrome are nausea and vomiting, and more seriously, neurological problems such as confusion or delirium. The syndrome has been associated with the use of aspirin to relieve flu symptoms.

Diagnosis

Although there are specific tests to identify the flu virus strain from respiratory samples, doctors typically rely on a set of symptoms and the presence of influenza in the community for diagnosis. Specific tests are useful to determine the type of flu in the community, but they do little for individual treatment. Doctors may administer tests, such as throat cultures, to identify secondary infections.

Since 1999, however, seven rapid diagnostic tests for flu have become commercially available. These tests appear to be especially useful in diagnosing flu in children, allowing doctors to make more accurate treatment decisions in less time.

Treatment

Essentially, a bout of influenza must be allowed to run its course. Symptoms can be relieved with bed rest and by keeping well hydrated. A steam vaporizer may make breathing easier, and pain relievers will take care of the aches and pain. Food may not seem very appetizing, but an effort should be made to consume nourishing food. Recovery should not be pushed too rapidly. Returning to normal activities too quickly invites a possible relapse or complications.

Drugs

Since influenza is a viral infection, antibiotics are useless in treating it. However, antibiotics are frequently used to treat secondary infections.

Over-the-counter medications are used to treat flu symptoms, but it is not necessary to purchase a medication marketed specifically for flu symptoms. Any medication that is designed to relieve symptoms, such as pain and coughing, will provide some relief. Medications containing alcohol, however, should be avoided because of the dehydrating effects of alcohol. The best medicine for symptoms is simply an analgesic, such as aspirin, acetaminophen, or naproxen. Without a doctor's approval, aspirin is generally not recommended for people under 18 owing to its association with Reye's syndrome, a rare aspirin-associated complication seen in children recovering from the flu. To be on the safe side, children should receive acetaminophen or ibuprofen to treat their symptoms.

There are four antiviral drugs marketed for treating influenza as of 2003. To be effective, treatment should begin no later than two days after symptoms appear. Antivirals may be useful in treating patients who have weakened immune systems or who are at risk for developing serious complications. They include amantadine (Symmetrel, Symadine) and rimantadine (Flumandine), which work against Type A influenza, and zanamavir (Relenza) and oseltamavir phosphate (Tamiflu), which work against both Types A and B influenza. Amantadine and rimantadine can cause side effects such as nervousness, anxiety, lightheadedness, and nausea. Severe side effects include seizures, delirium, and hallucination, but are rare and are nearly always limited to people who have kidney problems, seizure disorders, or psychiatric disorders. The new drugs zanamavir and oseltamavir phosphate have few side effects but can cause dizziness, jitters, and insomnia.

Alternative treatments

There are several alternative treatments that may help in fighting off the virus and recovering from the flu, in addition to easing flu symptoms.

  • Acupuncture and acupressure. Both are said to stimulate natural resistance, relieve nasal congestion and headaches, fight fever, and calm coughs, depending on the acupuncture and acupressure points used.
  • Aromatherapy. Aromatherapists recommend gargling daily with one drop each of the essential oils of tea tree (Melaleuca spp.) and lemon mixed in a glass of warm water. If already suffering from the flu, two drops of tea tree oil in a hot bath may help ease the symptoms. Essential oils of eucalyptus (Eucalyptus globulus ) or peppermint (Mentha piperita ) added to a steam vaporizer may help clear chest and nasal congestion.
  • Herbal remedies. Herbal remedies can be used stimulate the immune system (echinacea ), as antivirals (Hydrastis canadensis ) goldenseal and garlic (Allium sativum ), or directed at whatever symptoms arise as a result of the flu. For example, an infusion of boneset (Eupatroium perfoliatum ) may counteract aches and fever, and yarrow (Achillea millefolium ) or elderflower tinctures may combat chills.
  • Homeopathy. To prevent flu, a homeopathic remedy called Oscillococcinum may be taken at the first sign of flu symptoms and repeated for a day or two. Although oscillococcinum is a popular flu remedy in Europe, however, a research study published in 2003 found it to be ineffective. Other homeopathic remedies recommended vary according to the specific flu symptoms present. Gelsemium (Gelsemium sempervirens) is recommended to combat weakness accompanied by chills, a headache, and nasal congestion. Bryonia (Bryonia alba) may be used to treat muscle aches, headaches, and a dry cough. For restlessness, chills, hoarseness, and achy joints, poison ivy (Rhus toxicodendron ) is recommended. Finally, for achiness and a dry cough or chills, Eupatorium perfoliatum is suggested.
  • Hydrotherapy. A bath to induce a fever will speed recovery from the flu by creating an environment in the body where the flu virus cannot survive. The patient should take a bath as hot as he/she can tolerate and remain in the bath for 20-30 minutes. While in the bath, the patient drinks a cup of yarrow or elderflower tea to induce sweating. During the bath, a cold cloth is held on the forehead or at the nape of the neck to keep the temperature down in the brain. The patient is assisted when getting out of the bath (he/she may feel weak or dizzy) and then gets into bed and covers up with layers of blankets to induce more sweating.
  • Traditional Chinese medicine (TCM). Practitioners of TCM recommend mixtures of herbs to prevent flu as well as to relieve symptoms once a person has fallen ill. There are several different recipes for these remedies, but most contain ginger and Japanese honeysuckle in addition to other ingredients.
  • Vitamins. For adults, 2-3 grams of vitamin C daily may help prevent the flu. Increasing the dose to 5-7 grams per day during the flu can felp fight the infection. (The dose should be reduced if diarrhea develops.)

Prognosis

Following proper treatment guidelines, healthy people under the age of 65 usually suffer no long-term consequences associated with flu infection. The elderly and the chronically ill are at greater risk for secondary infection and other complications, but they can also enjoy a complete recovery.

Most people recover fully from an influenza infection, but it should not be viewed complacently. Influenza is a serious disease, and approximately 1 in 1,000 cases proves fatal.

Prevention

The Centers for Disease Control and Prevention recommend that people get an influenza vaccine injection each year before flu season starts. In the United States, flu season typically runs from late December to early March. Vaccines should be received two to six weeks prior to the onset of flu season to allow the body enough time to establish immunity. Adults only need one dose of the yearly vaccine, but children under nine years of age who have not previously been immunized should receive two doses with a month between each dose.

Each season's flu vaccine contains three virus strains that are the most likely to be encountered in the coming flu season. When there is a good match between the anticipated flu strains and the strains used in the vaccine, the vaccine is 70-90% effective in people under 65. Because immune response diminishes somewhat with age, people over 65 may not receive the same level of protection from the vaccine, but even if they do contract the flu, the vaccine diminishes the severity and helps prevent complications.

The virus strains used to make the vaccine are inactivated and will not cause the flu. In the past, flu symptoms were associated with vaccine preparations that were not as highly purified as modern vaccines, not to the virus itself. In 1976, there was a slightly increased risk of developing Guillain-Barré syndrome, a very rare disorder, associated with the swine flu vaccine. This association occurred only with the 1976 swine flu vaccine preparation and has never recurred.

Serious side effects with modern vaccines are extremely unusual. Some people experience a slight soreness at the point of injection, which resolves within a day or two. People who have never been exposed to influenza, particularly children, may experience one to two days of a slight fever, tiredness, and muscle aches. These symptoms start within 6-12 hours after the vaccination.

It should be noted that certain people should not receive an influenza vaccine. Infants six months and younger have immature immune systems and will not benefit from the vaccine. Since the vaccines are prepared using hen eggs, people who have severe allergies to eggs or other vaccine components should not receive the influenza vaccine. As an alternative, they may receive a course of amantadine or rimantadine, which are also used as a protective measure against influenza. Other people who might receive these drugs are those that have been immunized after the flu season has started or who are immunocompromised, such as people with advanced HIV disease. Amantadine and rimantadine are 70-90% effective in preventing influenza.

Certain groups are strongly advised to be vaccinated because they are at increased risk for influenza-related complications:

  • All people 65 years and older
  • Residents of nursing homes and chronic-care facilities, regardless of age
  • Adults and children who have chronic heart or lung problems, such as asthma
  • Adults and children who have chronic metabolic diseases, such as diabetes and renal dysfunction, as well as severe anemia or inherited hemoglobin disorders
  • Children and teenagers who are on long-term aspirin therapy
  • Women who will be in their second or third trimester during flu season or women who are nursing
  • Anyone who is immunocompromised, including HIV-infected persons, cancer patients, organ transplant recipients, and patients receiving steroids, chemotherapy, or radiation therapy
  • Anyone in contact with the above groups, such as teachers, care givers, health-care personnel, and family members
  • Travelers to foreign countries.

A person need not be in one of the at-risk categories listed above, however, to receive a flu vaccination. Anyone who wants to forego the discomfort and inconvenience of an influenza attack may receive the vaccine.

As of early 2003, researchers are working on developing an intranasal flu vaccine in aerosol form. An aerosol vaccine using a weakened form of Type A influenza virus has been tested in pilot studies and awaits further clinical trials.

Resources

BOOKS

Beers, Mark H., MD, and Robert Berkow, MD, editors. "Respiratory Viral Diseases: Influenza." Section 13, Chapter 162. In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Pelletier, Kenneth R., MD. The Best Alternative Medicine, Part II. "CAM Therapies for Specific Conditions: Colds/Flu." New York: Simon & Schuster, 2002.

PERIODICALS

Elkins, Rita. "Combat Colds and Flu." Let's Live. 68 (January 2000): 81+.

Jonas, W. B., T. J. Kaptchuk, and K. Linde. "A Critical Overview of Homeopathy." Annals of Internal Medicine 138 (March 4, 2003): 393-399.

Krug, R. M. "The Potential Use of Influenza Virus as an Agent for Bioterrorism." Antiviral Research 57 (January 2003): 147-150.

Oxford, J. S., S. Bossuyt, S. Balasingam, et al. "Treatment of Epidemic and Pandemic Influenza with Neuraminidase and M2 Proton Channel Inhibitors." Clinical Microbiology and Infection 9 (January 2003): 1-14.

Roth, Y., J. S. Chapnik, and P. Cole. "Feasibility of Aerosol Vaccination in Humans." Annals of Otology, Rhinology, and Laryngology 112 (March 2003): 264-270.

Shortridge, K. F., J. S. Peiris, and Y. Guan. "The Next Influenza Pandemic: Lessons from Hong Kong." Journal of Applied Microbiology 94, Supplement (2003): 70S-79S.

Storch, G. A. "Rapid Diagnostic Tests for Influenza." Current Opinion in Pediatrics 15 (February 2003): 77-84.

Thompson, W. W., D. K. Shay, E. Weintraub, et al. "Mortality Associated with Influenza and Respiratory Syncytial Virus in the United States." Journal of the American Medical Association 289 (January 8, 2003): 179-186.

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. http://www.cdc.gov.

National Institute of Allergy and Infectious Diseases (NIAID). 31 Center Drive, MSC 2520, Bethesda, MD 20892-2520. http://www.niaid.nih.gov.

OTHER

NIAID Fact Sheet: Flu. Bethesda, MD: NIAID, January 2003. http://www.niaid.nih.gov/factsheets/flu.htm.

KEY TERMS

Bioterrorism The intentional use of disease-causing microbes or other biologic agents to intimidate or terrorize a civilian population for political or military reasons. Type A influenza virus could be used as an agent of bioterrorism.

Common cold A mild illness caused by a upper respiratory viruses. Usual symptoms include nasal congestion, coughing, sneezing, throat irritation, and a low-grade fever.

Epidemic A widespread regional disease outbreak.

Guillain-Barré syndrome Also called acute idiopathic polyneuritis, this condition is a neurologic syndrome that can cause numbness in the limbs and muscle weakness following certain viral infections.

Pandemic Worldwide outbreak of an infection, afflicting millions of victims.

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Influenza

Influenza

Definition

Usually referred to as the flu or grippe, influenza is a highly infectious respiratory disease. Its name comes from the Italian word for "influence," because people in eighteenth-century Europe thought that the disease was caused by the influence of bad weather. We now know that flu is caused by a virus. When the influenza virus is inhaled, it attacks cells in the upper respiratory tract, causing such typical flu symptoms as fatigue, fever and chills , a hacking cough , and body aches. Although the stomach or intestinal "flu" is commonly blamed for stomach upsets and diarrhea , the influenza virus affects humans less often than is commonly believed.

Description

Influenza is considerably more debilitating than the common cold . Influenza outbreaks occur suddenly, and infection spreads rapidly. The annual death toll attributable to influenza and its complications averages 20,000 in the United States alone. In the 1918-1919 Spanish flu pandemic, the death toll reached a staggering 2040 million worldwide. Approximately 500,000 of these fatalities occurred in North America.

Influenza outbreaks occur on a regular basis. The most serious outbreaks are pandemics, which affect millions of people worldwide and last for several months. The 1918-19 influenza outbreak serves as the primary example of an influenza pandemic. Pandemics also occurred in 1957 and 1968 with the Asian flu and Hong Kong flu, respectively.

Epidemics are widespread regional outbreaks that occur every two to three years and affect 510% of the population. A regional epidemic is shorter lived than a pandemic, lasting only several weeks. Finally, there are smaller outbreaks each winter that are confined to specific locales.

There are three types of influenza viruses, identified as A, B, and C. Influenza A can infect a range of animal species, including humans, pigs, horses, and birds, but only humans are infected by types B and C. Influenza A is responsible for most flu cases, while infection with types B and C virus are less common and cause a milder illness.

In the United States, 90% of all deaths from influenza occur among persons older than 65. Flu-related deaths have increased substantially in the United States since the 1970s, largely because of the aging of the American population. In addition, elderly persons are vulnerable because they are often reluctant to be vaccinated against flu.

A new concern regarding influenza is the possibility that hostile groups or governments could use the virus as an agent of bioterrorism. A report published in early 2003 noted that Type A influenza virus has a high potential for use as such an agent because of the virulence of the Type A strain that broke out in Hong Kong in 1997 and the development of laboratory methods for generating large quantities of the virus. The report recommended the stockpiling of present antiviral drugs and speeding up the development of new ones.

Causes & symptoms

Approximately one to four days after infection with the influenza virus, the victim develops an array of symptoms. Symptoms are usually sudden, although the sequence can be quite variable. They include the onset of headache, sore throat , dry cough, and chills, nasal congestion, fatigue, malaise, overall achiness and a fever that may run as high as 104°F (40°C). Flu victims feel extremely tired and weak, and may not return to their normal energy levels for several days or weeks.

Influenza complications usually arise from bacterial infections of the lower respiratory tract. Signs of a secondary respiratory infection often appear just as the patient seems to be recovering. These signs include high fever, intense chills, chest pains associated with breathing, and a productive cough or sinus discharge with thick yellowish-green sputum. If these symptoms appear, medical treatment is often necessary. Other secondary infections, such as sinus or ear infections, may also require medical intervention. Heart and lung problems and other chronic diseases, can be aggravated by influenza, which is a particular concern with elderly patients.

With children and teenagers, it is advisable to be alert for symptoms of Reye's syndrome, a rare but serious complication that occurs when children are given aspirin. Symptoms of Reye's syndrome are nausea and vomiting ,

and more seriously, such neurological problems as confusion or delirium. The syndrome is primarily associated with the use of aspirin to relieve flu symptoms in children.

Diagnosis

Although there are specific laboratory tests to identify the flu virus strain from respiratory samples, doctors typically rely on a set of symptoms and the presence of influenza in the community for diagnosis. Specific tests are useful to determine the type of flu in the community, but they do little for individual treatment. Doctors may administer such tests as throat or sinus cultures or blood tests to identify secondary infections.

Since 1999, however, seven rapid diagnostic tests for flu have become commercially available. These tests appear to be especially useful in diagnosing flu in children, allowing doctors to make more accurate treatment decisions in less time.

Treatment

The patient should drink plenty of fluids and eat nutritious foods. Chicken soup with ginger , scallions, and rice noodles is nutritious and has healing powers. Rest, to allow the body to fight infection, is very important. Gargling with salt water (half teaspoon salt in one cup of water) helps to soothe a sore throat. A vaporizer with eucalyptus or Vicks VapoRub will make the patient feel more comfortable by easing breathing and aiding sleep. Applying Vicks ointment over chest and back will assist and speed recovery. Returning to normal activities too quickly invites a possible relapse or complications.

Herbals

Herbal teas and other preparations can be taken to stimulate the immune system, for antiviral activity, and to relieve symptoms. The following herbs are used to treat influenza:

  • Ginger (Zingiber officinalis ) reduces fever and pain , has a sedative effect, settles the stomach, and suppresses cough.
  • Forsythia (Forsythia suspensa ) fruit can be taken as a tea for its anti-inflammatory, fever-reducing, and antimicrobial properties.
  • Honeysuckle (Lonicera japonica ) flower can be taken as a tea for its anti-inflammatory, fever-reducing, and antimicrobial properties.
  • Anise seed (Pimpinella anisum ) can be added to tea to expel phlegm, induce sweating, ease nausea, and ease stomach gas.
  • Slippery elm (Ulmus rubra ) can be taken as a tea or slurry to soothe sore throat and ease cough.
  • Echinacea (Echinacea purpurea or angustifolia ), in clinical studies, reduced flu symptoms including sore throat, chills, sweating, fatigue, weakness, body aches, and headaches. The usual dosage is 500 mg thrice on the first day, then 250 mg four times daily thereafter.
  • Goldenseal (Hydrastis canadensis ) has fever reducing, antibacterial, anti-inflammatory, and antitussive properties. The usual dose is 125 mg three to four times daily. Goldenseal shouldn't be taken for more than one week.
  • Astragalus (Astragalus membranaceus ) boosts the immune system and improves the body's response to stress . The common dose is 250 mg of extract four times daily.
  • Cordyceps (Cordyceps sinensis ) modulates and boosts the immune system and improves respiration. The usual dose is 500 mg two to three times daily.
  • Elder (Sambucus nigra ) has antiviral activity, increases sweating, decreases inflammation, and decreases nasal discharge. In a study, elderberry extract reduced flu symptoms within two days whereas placebo took six days. The usual dose is 500 mg of extract thrice daily. Also use 2 tsp of dried flowers in 1 cup of water as a tea.
  • Schisandra (Schisandra chinensis ) helps the body fight disease and increases endurance.
  • Grape (Vitis vinifera ) seed extract has antihistamine and anti-inflammatory properties. The usual dose is 50 mg three times daily.
  • Eucalyptus (Eucalyptus globulus ) or peppermint (Mentha piperita ) essential oils added to a steam vaporizer may help clear chest and nasal congestion.
  • Boneset infusion (Eupatorium perfoliatum ) relieves aches and fever.
  • Yarrow (Achillea millefolium ) relieves chills.

Other remedies

Acupuncture and acupressure are said to stimulate natural resistance, relieve nasal congestion and headaches, fight fever, and calm coughs, depending on the points used.

A homeopathic remedy called Oscillococcinum may be taken at the first sign of flu symptoms and repeated for a day or two. This remedy is said to shorten the duration of flu by one or two days. Although oscillococcinum is a popular flu remedy in Europe, however, a research study published in 2003 found it to be ineffective.

Other homeopathic remedies recommended vary according to the specific flu symptoms present. Gelsemium (Gelsemium sempervirens ) is recommended to combat weakness accompanied by chills, a headache, and nasal congestion. Bryonia (Bryonia alba ) may be used to treat muscle aches, headaches, and a dry cough. For restlessness, chills, hoarseness, and achy joints, poison ivy (Rhus toxicodendron ) is recommended. Finally, for achiness and a dry cough or chills, Eupatorium perfoliatum is suggested.

Hydrotherapy can be utilized. A bath to induce a fever will speed recovery from the flu. While supervised, the patient should take a bath as hot as he/she can tolerate and remain in the bath for 2030 minutes. While in the bath, the patient drinks a cup of yarrow or elder-flower tea to induce sweating. During the bath, a cold cloth is held on the forehead or at the nape of the neck to keep the temperature down. The patient is assisted when getting out of the bath (he/she may feel weak or dizzy) and then gets into bed and covers up with layers of blankets to induce more sweating.

Supplemental vitamins are recommended for treating influenza, and include 5002000 mg vitamin C , 400 IU to 500 IU of vitamin E , 200 micrograms to 300 micrograms selenium , and 25,000 IU beta-carotene. Zinc lozenges are helpful, as is supplemental zinc at 25 mg per day for two weeks or more.

Traditional Chinese medicine (TCM) uses mixtures of herbs to prevent flu as well as to relieve symptoms once a person has fallen ill. There are several different recipes for these remedies, but most contain ginger and Japanese honeysuckle in addition to other ingredients.

Allopathic treatment

Because influenza is a viral infection, antibiotics are useless in treating it. However, antibiotics are frequently used to treat secondary infections.

Over-the-counter medications are used to treat flu symptoms. Any medication that is designed to relieve such symptoms as pain and coughing will provide some relief. The best medicine for symptoms is an analgesic, such as aspirin, acetaminophen, or naproxen. Without a doctor's approval, aspirin is generally not recommended for people under 18 owing to its association with Reye's syndrome, a rare aspirin-associated complication seen in children recovering from viral infections. Children should receive acetaminophen or ibuprofen to treat their symptoms.

There are four antiviral drugs marketed for treating influenza as of 2003. To be effective, treatment should begin no later than two days after symptoms appear. Antivirals may be useful in treating patients who have weakened immune systems or who are at risk for developing serious complications. They include amantadine (Symmetrel, Symadine) and rimantadine (Flumandine), which work against Type A influenza; and zanamavir (Relenza) and oseltamavir phosphate (Tamiflu), which work against both Types A and B influenza. Amantadine and rimantadine can cause such side effects as nervousness, anxiety , lightheadedness, and nausea. Severe side effects include seizures, delirium, and hallucination, but are rare and are nearly always limited to people who have kidney problems, seizure disorders, or psychiatric disorders. The new drugs zanamavir and oseltamavir phosphate have few side effects but can cause dizziness , jitters, and insomnia .

Expected results

Following proper treatment guidelines, healthy people under the age of 65 usually suffer no long-term consequences associated with flu infection. The elderly and the chronically ill are at greater risk for secondary infection and other complications, but they can also enjoy a complete recovery.

Most people recover fully from an influenza infection, but it should not be viewed complacently. Influenza is a serious disease, and approximately 1 in 1,000 cases proves fatal.

Prevention

The Centers for Disease Control and Prevention recommend that people get an influenza vaccine injection each year before flu season starts. In the United States, flu season typically runs from late December to early March. Vaccines should be received two to six weeks prior to the onset of flu season to allow the body enough time to establish immunity.

Each season's flu vaccine contains three virus strains that are the most likely to be encountered in the coming flu season. The virus strains used to make the vaccine are inactivated and will not cause illness. When there is a good match between the anticipated flu strains and the strains used in the vaccine, the vaccine is 70-90% effective in people under 65. Because immune response diminishes somewhat with age, people over 65 may not receive the same level of protection from the vaccine, but even if they do contract the flu, the vaccine diminishes the severity and helps prevent complications.

It should be noted that certain people should not receive an influenza vaccine. Infants six months and younger have immature immune systems and will not benefit from the vaccine. Because the vaccines are prepared using hen eggs, people who have severe allergies to eggs or other vaccine components should not receive the influenza vaccine. Some persons may receive a course of amantadine or rimantadine, which are 70-90% effective in preventing influenza.

Certain groups are strongly advised to be vaccinated because they are at greater risk for influenza-related complications:

  • All people 65 years and older.
  • Residents of nursing homes and chronic-care facilities.
  • Adults and children who have chronic heart or lung problems.
  • Adults and children who have chronic metabolic diseases, such as diabetes and renal dysfunction, as well as severe anemia or inherited hemoglobin disorders.
  • Children and teenagers who are on long-term aspirin therapy.
  • Anyone who is immunocompromised, including HIV-infected persons, cancer patients, organ transplant recipients, and patients receiving steroids, chemotherapy, or radiation therapy.
  • Anyone in contact with the above groups, such as teachers, care givers, health-care personnel, and family members.
  • Travelers to foreign countries.

As of early 2003, researchers are working on developing an intranasal flu vaccine in aerosol form. An aerosol vaccine using a weakened form of Type A influenza virus has been tested in pilot studies and awaits further clinical trials.

The following dietary supplements may be taken to help prevent influenza:

  • Elderberry prevents influenza virus from infecting cells.
  • Astragalus: 250500 mg daily.
  • Multivitamins with zinc.
  • Vitamin C; 500 mg.
  • Echinacea; at the first sign of malaise or infection, take 35 ml of tincture or 2 tablets three or four times daily for three to 10 days.

Resources

BOOKS

Pelletier, Kenneth R., MD. The Best Alternative Medicine, Part II, "CAM Therapies for Specific Conditions: Colds/Flu." New York: Simon & Schuster, 2002.

"Respiratory Viral Diseases: Influenza." Section 13, Chapter 162 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.

PERIODICALS

Elkins, Rita. "Combat Colds and Flu." Let&#39;s Live. 68 (January 2000): 81+.

Jonas, W. B., T. J. Kaptchuk, and K. Linde. "A Critical Overview of Homeopathy." Annals of Internal Medicine 138 (March 4, 2003): 393399.

Krug, R. M. "The Potential Use of Influenza Virus as an Agent for Bioterrorism." Antiviral Research 57 (January 2003): 147150.

La Valle, James B., and Ernie Hawkins. "Colds and Flu: A Natural Approach." Drug Store News. 20 (12/14/98): CP17+.

Oxford, J. S., S. Bossuyt, S. Balasingam, et al. "Treatment of Epidemic and Pandemic Influenza with Neuraminidase and M2 Proton Channel Inhibitors." Clinical Microbiology and Infection 9 (January 2003): 114.

Roth, Y., J. S. Chapnik, and P. Cole. "Feasibility of Aerosol Vaccination in Humans." Annals of Otology, Rhinology, and Laryngology 112 (March 2003): 264270.

Shortridge, K. F., J. S. Peiris, and Y. Guan. "The Next Influenza Pandemic: Lessons from Hong Kong." Journal of Applied Microbiology 94 (2003 Supplement): 70S79S.

Storch, G. A. "Rapid Diagnostic Tests for Influenza." Current Opinion in Pediatrics 15 (February 2003): 7784.

Thompson, W. W., D. K. Shay, E. Weintraub, et al. "Mortality Associated with Influenza and Respiratory Syncytial Virus in the United States." Journal of the American Medical Association 289 (January 8, 2003): 179186.

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Road, NE, Atlanta, Georgia 30333. (888) CDC-FACTS (888-232-3228). <http://www.cdc.gov/>.

National Institute of Allergy and Infectious Diseases (NIAID). 31 Center Drive, MSC 2520, Bethesda, MD 20892-2520. <http://www.niaid.nih.gov>.

OTHER

NIAID Fact Sheet: Flu. Bethesda, MD: NIAID, January 2003. <http://www.niaid.nih.gov/factsheets/flu.htm>.

Belinda Rowland

Rebecca J. Frey, PhD

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Influenza

Influenza

Definition

Usually referred to as the flu or grippe, influenza is a highly infectious respiratory disease. The disease is caused by certain strains of the influenza virus. When the virus is inhaled, it attacks cells in the upper respiratory tract, causing typical flu symptoms such as fatigue, fever and chills, a hacking cough , and body aches. Influenza victims are also susceptible to potentially life-threatening secondary infections. Although the stomach or intestinal "flu" is commonly blamed for stomach upsets and diarrhea , the influenza virus rarely causes gastrointestinal symptoms. Such symptoms are most likely due to other organisms such as rotavirus, Salmonella, Shigella, or Escherichia coli.

Description

The flu is considerably more debilitating than the common cold . Influenza outbreaks occur suddenly, and infection spreads rapidly. In the 191819 Spanish flu pandemic, the death toll reached a staggering 20 to 40 million worldwide. Approximately 500,000 of these fatalities occurred in the United States.

Influenza outbreaks occur on a regular basis. The most serious outbreaks are pandemics, which affect millions of people worldwide and last for several months. The 191819 influenza outbreak serves as the primary example of an influenza pandemic. Pandemics also occurred in 1957 and 1968 with the Asian flu and Hong Kong flu, respectively. The Asian flu was responsible for 70,000 deaths in the United States, while the Hong Kong flu killed 34,000.

Epidemics are widespread regional outbreaks that occur every two to three years and affect 510 percent of the population. The Russian flu in the winter of 1977 is an example of an epidemic. A regional epidemic is shorter lived than a pandemic, lasting only several weeks. Finally, there are smaller outbreaks each winter that are confined to specific locales.

The earliest existing descriptions of influenza were written nearly 2,500 years ago by the ancient Greek physician Hippocrates. Historically, influenza was ascribed to a number of different agents, including "bad air" and several different bacteria. In fact, its name comes from the Italian word for "influence," because people in eighteenth-century Europe thought that the disease was caused by the influence of bad weather. It was not until 1933 that the causative agent was identified as a virus.

There are three types of influenza viruses, identified as A, B, and C. Influenza A can infect a range of animal species, including humans, pigs, horses, and birds, but only humans are infected by types B and C. Influenza A is responsible for most flu cases, while infection with types B and C virus are less common and cause a milder illness.

Demographics

The annual death toll attributable to influenza and its complications averages 20,000 in the United States alone. In the United States, 90 percent of all deaths from influenza occur among persons older than 65. Flu-related deaths have increased substantially in the United States since the 1970s, largely because of the aging of the American population. In addition, elderly persons are vulnerable because they are often reluctant to be vaccinated against flu.

Hospitalization due to complications of influenza are common in children. Among children with chronic illnesses, about 500 children per every 100,000 between the ages of birth and age four are hospitalized annually due to influenza, while about 100 children per 100,000 without chronic illnesses are hospitalized annually. Among those with underlying high-risk conditions, infants younger than six months have the highest hospitalization rates (approximately 1040 per 100,000 population).

Causes and symptoms

Approximately one to four days after infection with the influenza virus, the victim is hit with an array of symptoms. "Hit" is an appropriate term, because symptoms are sudden, harsh, and unmistakable. Typical influenza symptoms include the abrupt onset of a headache , dry cough, and chills, rapidly followed by overall achiness and a fever that may run as high as 104°F (40°C). As the fever subsides, nasal congestion and a sore throat become noticeable. Flu victims feel extremely tired and weak and may not return to their normal energy levels for several days or even a couple of weeks.

Influenza complications usually arise from bacterial infections of the lower respiratory tract. Signs of a secondary respiratory infection often appear just as the victim seems to be recovering. These signs include high fever, intense chills, chest pains associated with breathing, and a productive cough with thick yellowish green sputum. If these symptoms appear, medical treatment is necessary. Other secondary infections, such as sinus or ear infections may also require medical intervention. Children with heart and lung problems, as well as other chronic diseases, are at higher risk for complications from influenza.

With children and teenagers, it is advisable to be alert for symptoms of Reye's syndrome , a rare, but serious complication. Symptoms of Reye's syndrome are nausea and vomiting , and more seriously, neurological problems such as confusion or delirium. The syndrome has been associated with the use of aspirin to relieve flu symptoms.

Diagnosis

Although there are specific viral culture tests available to identify the flu virus strain from respiratory samples, results can take several days. Therefore, doctors typically rely on a set of symptoms and the presence of influenza in the community for diagnosis. Specific tests are useful to determine the type of flu in the community, but they do little for individual treatment. Doctors may administer tests, such as throat cultures, to identify secondary infections.

Several rapid (30-minute) diagnostic tests for flu have become commercially available. These tests appear to be especially useful in diagnosing flu in children, allowing doctors to make more accurate treatment decisions in less time.

Treatment

Essentially, a bout of influenza must be allowed to run its course. Symptoms can be relieved with bed rest and by keeping well hydrated. A steam vaporizer may make breathing easier, and pain relievers can mask the aches and pain. Food may not seem very appetizing, but an effort should be made to consume nourishing food. Recovery should not be pushed. Returning to normal activities too quickly invites a possible relapse or complications.

Drugs

Since influenza is a viral infection, antibiotics are useless in treating it. However, antibiotics are frequently used to treat secondary infections.

Over-the-counter medications are used to treat flu symptoms, but it is not necessary to purchase a medication marketed specifically for flu symptoms. Any medication that is designed to relieve symptoms, such as pain and coughing, will provide some relief. Medications containing alcohol, however, should be avoided because of the dehydrating effects of alcohol. The best medicine for symptoms is simply an analgesic, such as acetaminophen or naproxen. (Without a doctor's approval, aspirin is generally not recommended for people under 18 owing to its association with Reye's syndrome, a rare aspirin-associated complication seen in children recovering from the flu. To be on the safe side, children should receive acetaminophen or ibuprofen to treat their symptoms.)

As of 2004, there were a number of antiviral drugs marketed for treating influenza. To be effective, treatment should begin no later than two days after symptoms appear. These medications are useful for decreasing the severity and duration of symptoms. Antivirals may be useful in treating patients who have weakened immune systems or who are at risk for developing serious complications. They include amantadine (Symmetrel, Symadine) and rimantadine (Flumandine), which work against Type A influenza, and zanamavir (Relenza) and oseltamavir phosphate (Tamiflu), which work against both Types A and B influenza. Amantadine and rimantadine can cause side effects such as nervousness, anxiety , lightheadedness, and nausea . Severe side effects include seizures, delirium, and hallucination, but are rare and are nearly always limited to people who have kidney problems, seizure disorders, or psychiatric disorders. Zanamavir and oseltamavir phosphate can cause dizziness , jitters, and insomnia.

Prognosis

Following proper treatment guidelines, healthy people under the age of 65 usually suffer no long-term consequences associated with flu infection. The elderly and the chronically ill are at greater risk for secondary infection and other complications, but they can also enjoy a complete recovery.

Most people recover fully from an influenza infection, but it should not be viewed complacently. Influenza is a serious disease, and approximately one in 1,000 cases proves fatal.

Prevention

The Centers for Disease Control and Prevention recommends that people get an influenza vaccine injection each year before flu season starts. In the United States, flu season typically runs from late December to early March. Vaccines should be received two to six weeks prior to the onset of flu season to allow the body enough time to establish immunity. Adults only need one dose of the yearly vaccine, but children under nine years of age who have not previously been immunized should receive two doses with a month between each dose.

Each season's flu vaccine contains three virus strains that are the most likely to be encountered in the coming flu season. When there is a good match between the anticipated flu strains and the strains used in the vaccine, the vaccine is 7090 percent effective in people under 65. Because immune response diminishes somewhat with age, people over 65 may not receive the same level of protection from the vaccine, but even if they do contract the flu, the vaccine diminishes the severity and helps prevent complications.

The virus strains used to make the vaccine are inactivated and will not cause the flu. In the second half of the twentieth century, flu symptoms were associated with vaccine preparations that were not as highly purified as modern vaccines, not to the virus itself. In 1976, there was a slightly increased risk of developing Guillain-Barré syndrome, a very rare disorder, associated with the swine flu vaccine. This association occurred only with the 1976 swine flu vaccine preparation and as of 2004 had not recurred.

Serious side effects with modern vaccines are extremely unusual. Some people experience a slight soreness at the point of injection, which resolves within a day or two. People who have never been exposed to influenza, particularly children, may experience one to two days of a slight fever, tiredness, and muscle aches. These symptoms start within six to 12 hours after the vaccination .

It should be noted that certain people should not receive an influenza vaccine. Infants six months and younger have immature immune systems and will not benefit from the vaccine. Since the vaccines are prepared using hen eggs, people who have severe allergies to eggs or other vaccine components should not receive the influenza vaccine. As an alternative, they may receive a course of amantadine or rimantadine, which are also used as a protective measure against influenza. Other people who might receive these drugs are those that have been immunized after the flu season has started or who are immunocompromised, such as people with advanced HIV disease. Amantadine and rimantadine are 7090 percent effective in preventing influenza.

Certain groups are strongly advised to be vaccinated because they are at increased risk for influenza-related complications. These groups are:

KEY TERMS

Common cold A mild illness caused by upper respiratory viruses. Usual symptoms include nasal congestion, coughing, sneezing, throat irritation, and a low-grade fever.

Epidemic Refers to a situation in which a particular disease rapidly spreads among many people in the same geographical region in a relatively short period of time.

Guillain-Barré syndrome Progressive and usually reversible paralysis or weakness of multiple muscles usually starting in the lower extremities and often ascending to the muscles involved in respiration. The syndrome is due to inflammation and loss of the myelin covering of the nerve fibers, often associated with an acute infection. Also called acute idiopathic polyneuritis.

Pandemic A disease that occurs throughout a regional group, the population of a country, or the world.

  • children under age two
  • all people 65 years and older
  • residents of nursing homes and chronic-care facilities, regardless of age
  • adults and children who have chronic heart or lung problems, such as asthma
  • adults and children who have chronic metabolic diseases, such as diabetes and renal dysfunction, as well as severe anemia or inherited hemoglobin disorders
  • children and teenagers who are on long-term aspirin therapy
  • women who will be in their second or third trimester during flu season or women who are nursing
  • anyone who is immunocompromised, including HIV-infected persons, cancer patients, organ transplant recipients, and patients receiving steroids, and those receiving chemotherapy or radiation therapy
  • anyone in contact with the above groups, such as teachers, care givers, healthcare personnel, and family members
  • travelers to foreign countries

A person need not be in one of the at-risk categories listed above, however, to receive a flu vaccination. Anyone who wants to forego the discomfort and inconvenience of an influenza attack may receive the vaccine.

Parental concerns

Parents should make sure that their children who fall into any of the risk categories should be vaccinated against the flu. Pregnant women in the second or third trimesters should also be vaccinated. Flu vaccines are available through pediatricians or local public health departments. Parents should also make sure kids follow good hygiene practices, including regular hand washing, and covering the mouth when sneezing or coughing. Children may acquire secondary infections, such as ear infections or sinus infections, so parents should call the pediatrician if a child develops a high fever, sudden pain in the ears or sinuses, or develops a productive cough with thick yellow-green phlegm.

Resources

BOOKS

Subbarao, Kanta. "Influenza Viruses." In Principles and Practice of Pediatric Infectious Diseases, 2nd ed. Edited by Sarah S. Long et al. St. Louis, MO: Elsevier, 2003.

Wright, Peter. "Influenza Viruses." In Nelson Textbook of Pediatrics. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.

PERIODICALS

Larkin, M. "Will influenza be the next bioweapon?" Lancet Infectious Disease 138 (January 7, 2003): 53.

Neff, M. J. "ACIP Releases 2004 Guidelines on the Prevention and Control of Influenza." Annals of Internal Medicine 70) (July 2004): 199204.

Stiver, G. "The treatment of influenza with antiviral drugs." Canadian Medical Association Journal 138 (January 2003): 4956.

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. Web site: <www.cdc.gov>.

National Institute of Allergy and Infectious Diseases (NIAID). 31 Center Drive, MSC 2520, Bethesda, MD 208922520. Web site: <www.niaid.nih.gov>

WEB SITES

"Flu." Health Matters, November 2004. Available online at <www.niaid.nih.gov/factsheets/flu.htm> (accessed December 28, 2004).

Julia Barrett Rebecca J. Frey, PhD Rosalyn Carson-DeWitt, MD

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Influenza

INFLUENZA

Influenza is a potentially severe acute respiratory illness caused by various strains of the influenza virus. The different strains all produce characteristic symptoms, and because major outbreaks are associated with increased mortality, occurrences can be identified in history. Outbreaks consistent with influenza can be traced back at least to the court of Elizabeth I. Some have speculated that the Plague of Athens described by Thucydides was influenza complicated by bacterial superinfection. The influenza syndrome, commonly known as the flu, with its fever, cough, rapid onset and body aches, is not only typical enough to be recognized in the past, but it also allows physicians to recognize it, especially when it is known that the virus is circulating. Unfortunately, death is the other consistent phenomena associated with influenza. Mortality statistics are the principal way the intensity of an influenza outbreak is quantified, and are so characteristic that viral identification of etiology is not required.

THE VIRUS AND ITS ANTIGENS

The influenza viruses contain RNA (ribonucleic acid) and are somewhat unusual in that they have a segmented genome, which means that there are eight distinct segments to the single-stranded RNA. Influenza types A and B are the only strains with epidemic potential; type C viruses are difficult to work with in the laboratory and are one of the multiple agents able to cause the common cold. While the viruses are classified into type A and B on the basis of their internal components, it is the surface antigens that are important in eliciting antibodies that will protect against future infection. These surface antigens and their changes make influenza challenging to control. Two types of changes are recognized.

One change occurs in both type A and B viruses and is a result of point mutations in the segments of the genome coding for two specific surface antigens (the neuraminidase [N] and the hemagglutinin [H] segments). These mutations are the reason that both type A and B viruses change regularly from year to year, though type A changes somewhat more rapidly than type B. Such changes are referred to as "antigen drift." Another change is more dramatic, only occurring with type A viruses, and is an example of "antigen shift." It takes place when one or two gene segments are replaced in a circulating virus. The same two antigens, or proteins, are involved in both types of change. The various influenza A viruses are categorized into subtypes by the differences in those two antigens, such as A (H1N1) or A (H3N2).

The most widely accepted theory explaining this antigen shift is that the segments come from animal influenza viruses. Type B influenza is confined to humans, while type A exists in numerous species of birds and domestic animals. There are fifteen types of hemagglutinin in the influenza virus of birds, but only three in human viruses, which gives an ample opportunity for the segment coding for the hemagglutinin to move from avian viruses to human. This has apparently happened in the past, and is likely to occur in the future, either directly or through pigs. In 1997, in Hong Kong, an avian virus infected humans directly, but did not become adapted to humans by exchange of gene segments. If it had, a pandemic undoubtedly would have resulted.

PANDEMICS: HISTORY AND IMPACT

While some trace influenza pandemics back to ancient Greece, the first documented occurrence was in 1889 (see Table 1). In that and subsequent years, outbreaks of influenza were reported in many areas of the world, and in the United States, deaths reported in the state of Massachusetts for the first time demonstrated the U- or J-shaped mortality curvean elevated mortality in young children, low mortality until age forty-five, followed by gradually increasing mortality with a relatively sharp inflection upward at age sixty-five (see Figure 1). By testing blood specimens of persons who lived through this period, researchers have been able to hypothesize about the strain of virus that caused this pandemic. In 1899, there was an apparent antigen shift, but this was determined serologically, not on the basis of an observed pandemic.

It is now certain that a virus resembling one isolated from pigs in the 1930s caused the devastating 1918 pandemic. No influenza viruses were isolated until the 1930s, so that any identification of viruses responsible for events occurring before that time has traditionally been done by testing the blood of people living through the period of an outbreak. Confirmation of this approach has recently taken place using modern molecular technique involving tissue of individuals who died during the 1918 pandemic. The virus is now termed A(H1N1). The estimated death toll from this pandemic has been revised upwards from 20 million to 40 million, since large segments of the world mainly the current developing countrieswere originally omitted from the counts. The lethality of this pandemic was related in large part to the death of an unexpectedly large number of healthy

Table 1

Pandemics caused by type A influenza
Year A Subtype Popular Name Impact
source: Courtesy of author.
1889 H2N2 Severe
1899 H3N8 Not recognized
1918 H1N1 Spanish flu Catastrophic
1957 H2N2 Asian flu Severe
1968 H3N2 Hong Kong flu Intermediate
1977 H1N1 Russian flu Pandemic in younger people
1998 H5N2 Avian flu Cluster of human cases

young adults. This resulted in a W-shaped agespecific mortality curve (see Figure 1). It is hoped that genetic research with lung tissue, either stored or recovered from bodies, will enable epidemiologists to predict the potential behavior of future pandemic strains of influenza when they are identified. However, this has not as yet been possible, so it is only by observing the epidemiology of infection that the age-specific pattern of illness can be determined.

The first influenza viruses were isolated from humans in the early 1930s. However, the next pandemic did not occur until 1957, when the A(H2N2) virus appeared in South China (see Figure 1). The pandemic that resulted was the most severe since 1918, but again exhibited the more typical U-shaped mortality curve, concentrated in very young children and older individuals. A little more than ten years later, in 1968, the hemagglutinin changed and the resulting pandemic was similar to 1957 in age distribution, but more moderate in overall impact.

Two more episodes have occurred since 1968 that had the potential to be full pandemics. In 1977, the A(H1N1) virus returned, with outbreaks occurring first in China and then in the former Soviet Union. Since the virus had circulated twenty or more years before, when worldwide outbreaks occurred, these epidemics were confined to younger individuals. This virus has continued to circulate, along with the A(H3N2) and B viruses. Finally, in 1997, A(H5N1) moved from chickens to humans in Hong Kong. There were eighteen confirmed cases, with six deaths that were not restricted to older individuals. Fortunately, this avian virus did not

Figure 1

become fully adapted to humans. No human-to-human transmission was observed, but this episode showed how a catastrophic pandemic might have occurred had such adaptation taken place.

PREVENTION AND CONTROL OF INFLUENZA

A vaccine for the prevention of influenza was developed during World War II in order to maintain military readiness. This was done in recognition of the high morbidity that could result among troops exposed to the virus. A similar inactivated vaccine is still in use, improved in both potency and lack of side effects. It is known to be 70 to 90 percent efficacious in healthy young adults as long as the vaccine viruses resemble those circulating. This necessitates updating the viruses in the vaccine each year. For this and other reasons, the vaccine must be given annually. Since vaccination programs must be sustained, the goal in most countries has been to reduce influenza mortality by vaccinating older individuals and those with chronic underlying diseases. An exception to this has been Japan, where, for a time, school-age children were vaccinated in an effort to control influenza morbidity. It has been repeatedly demonstrated that the inactivated vaccine is effective in preventing hospitalization and death in older individuals and, as such, is also cost effective. The inactivated vaccine is cost effective in healthy adults only when the attack rates are above 12 percent. A live attenuated influenza vaccine has been used in the former Soviet Union for many years, and another is in development in the United States. Because of its deliveryintranasally rather than by injectionit may prove to be particularly useful in children and younger adults.

Antiviral drugs have been available both for treatment and prophylaxis. Two of these are active only against type A viruses. A new group of drugs, acting as neuraminidase inhibitors, is active against both type A and B viruses. These drugs have been shown to have a prevention efficacy similar to vaccines. They start protecting more quickly than the vaccine, but have to be taken daily to continue protection. Therefore, vaccination will continue to be the usual means of prophylaxis. The neuraminidase inhibitors also significantly shorten the duration of illness, reducing severity and preventing complications. Influenza can be debilitating, even in the absence of complications, so that the drugs will be used for treatment during defined influenza outbreaks. They are likely also to be useful prophylactically, especially for outbreak control in nursing homes.

Arnold Monto

Bibliography

Belshe, R. B.; Mendelman, P. M.; Treanor, J. et al. (1998). "The Efficacy of Live Attenuated, Cold-adapted, Trivalent, Intranasal Influenza Virus Vaccine in Children." New England Journal of Medicine 149:11131117.

Dolin, R.; Reichman, R. C.; Madore, H. P.; Maynard, R.; Linton, P. N.; and Webber-Jones, J. (1982). "A Controlled Trial of Amantadine and Rimantadine in the Prophylaxis of Influenza A Infection." New England Journal of Medicine 307:580584.

Douglas, R. B., Jr. (1990). "Drug Therapy: Prophylaxis and Treatment of Influenza." New England Journal of Medicine 322:443450.

Eickhoff, T. C.; Sherman, I. L.; and Serfling, R. E. (1961). "Observations on Excess Mortality Associated with Epidemic Influenza." Journal of the American Medical Association 176:776782.

Gubareva, L. B.; Kaiser, L.; and Hayde, F. G. (2000). "Influenza Virus Neuraminidase Inhibitors." New England Journal of Medicine 355:827835.

Lui, K. J., and Kendal, A. P. (1987). "Impact of Influenza Epidemics on Mortality in the United States from October 1972 to May 1985." American Journal of Public Health 77:712716.

Monto, A. S., and Arden, N. H. (1992). "Implications of Viral Resistance to Amantadine in Control of Influenza A." Clinical Infectious Diseases 15:362367.

Monto, A. S., and Kioumehr, F. (1975). "The Tecumseh Study of Respiratory Illness. IX. Occurrence of Influenza in the Community, 19661971." American Journal of Epidemiology 102:553563.

Patriarca, P. A.; Weber, J. A.; Parker, R. A. et al. (1985). "Efficacy of Influenza Vaccine in Nursing Homes: Reduction in Illness and Complications During an Influenza A (H3N2) Epidemic." Journal of the American Medical Association 253:11361139.

Sullivan, F. M.; Monto, A. S.; and Longini, I. M., Jr. (1993). "Estimates of the U.S. Health Impact of Influenza." American Journal of Public Health 83: 17121716.

Wilde, J. A.; McMillan, J. A.; Serwint, J.; Butta, J; O'Riordan, M. A.; and Steinhoff, M. C. (1999). "Effectiveness of Influenza Vaccine in Health Care Professionals: A Randomized Trial." Journal of the American Medical Association 281:908913.

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Influenza

INFLUENZA

Influenza is an acute respiratory illness caused by infection with influenza type A or B virus. It typically occurs in outbreaks over a five-to six-week period each winter. Each year, hundreds of thousands of excess hospitalizations, tens of thousands of excess deaths, and billions of dollars in health care costs can be attributed to influenza and its complications. Attack rates can be as high as 10 to 40 percent in the community, and examination of influenza epidemic curves typically reveals a bimodal pattern, with attack rates highest in the young and morbidity and mortality highest in the elderly population. In most studies, elderly persons with chronic respiratory conditions account for up to 80 percent of patients with such serious complications as hospitalization and death.

Influenza can be a particularly difficult problem for people who live in long-term care facilities (LTCFs), where case fatality rates during outbreaks often exceed 5 percent. Up to 22 percent of residents that acquire influenza will develop complications of infection severe enough to result in hospitalization. Once influenza is introduced into a LTCF by staff and visitors, these relatively closed communities are an ideal setting for the rapid spread of influenza by droplet transmission. Attack rates among residents can exceed 40 percent.

Clinical findings

Influenza is typically characterized by the abrupt onset of fever, chills, headaches, severe myalgias (muscle pains), malaise, and loss of appetite. These are evident after an incubation period of one to two days. In the first three days of illness, headache and muscle pain are usually the most bothersome symptoms, with the severity of these complaints reflecting the magnitude of the fever. Dry cough, severe sore throat, and nasal obstruction and discharge are usually also present, although they may be overshadowed by the systemic complaints. The fever typically resolves after approximately three days, but the cough, sore throat, and hoarseness may persist for three to four days after the fever resolves. It is important to remember that in frail older adults disease presentation can be atypical. For example, some individuals might present only with fever, lack of energy, or confusion, and without any evidence of respiratory illness. Influenza should be considered in any illness characterized by fever in an elderly person during influenza season.

Without complications, influenza is a self-limited illness lasting five to eight days. Elderly patients and patients with high-risk medical conditions, including chronic lung or heart disease, kidney disease, problems with the immune system, cancer, or other chronic medical problems are at risk for developing complications from influenza. Pneumonia caused by the influenza virus itself and secondary bacterial pneumonia are the most common and serious complications of influenza. Patients with influenza pneumonia, a complication which is fortunately quite rare, will present with typical signs and symptoms of influenza but go on to develop severe cough, shortness of breath, and cyanosis. Chest X-rays will usually show bilateral findings most consistent with adult respiratory distress syndrome, and gram stains of sputum will not identify a bacterial pathogen. Death, due to diffuse hemorrhagic pneumonia, is high even with prompt antiviral therapy.

Secondary bacterial pneumonia is indistinguishable from community-acquired pneumonia in the absence of influenza, except that it typically occurs in elderly patients or patients with chronic heart or lung problems after recovery from a classic influenza illness. Patients will usually describe a recurrence of fever, cough, and sputum production four to fourteen days after their initial recovery from influenza. Physical examination and chest X-ray usually reveal a focal area of lung infection. Microbiological examination of the sputum often shows bacteria such as Streptococcus pneumoniae or Haemophilus influenzae. Treatment of community-acquired pneumonia as a secondary complication of influenza infection is not different than in any other setting, and requires antibiotic drugs.

Diagnosis

Influenza virus can be readily isolated from nasal swabs, throat swabs, nasal washes, and sometimes sputum. A throat swab alone is less sensitive than nasal or throat washes, and thus washes are preferred. Specimens should be placed into containers of viral transport medium and transported to the laboratory for viral culture. Two-thirds of positive cultures will be detected within seventy-two hours, with the remainder within five to seven days. However, particularly for influenza detection in long-term care facilities, faster methods of detection are needed. A variety of rapid detection methods for influenza virus exist that detect viral antigens by immunofluorescence or ELISA in as little as one hour, with reasonable sensitivity and specificity under optimal conditions. At present though, viral culture remains the gold standard for diagnosis of influenza infection.

Treatment

In otherwise healthy children and adults with uncomplicated influenza infection, antiviral therapy is not generally warranted. Bed rest, adequate fluid intake, and treatment with analgesics, cough suppressants, and decongestants may improve symptoms. In patients at significant risk for the development of complications of influenza, or in those with influenza pneumonia, the use of antiviral medications may decrease morbidity and mortality. Until recently, therapy for influenza typically involved the use of amantadine or rimantadine, antiviral drugs active against influenza A. Most studies examining the efficacy of these drugs have shown a reduction in clinical symptom scores, a faster resolution of fever, and a decrease in the level and duration of infectivity. Most authorities support the use of amantadine in the treatment of complicated influenza A virus infection, even late in the course of illness. Treatment with antiviral medications is also generally recommended for outbreaks of influenza A virus infection in LTCFs, although whether these drugs prevent illness, relieve symptoms, or reduce the duration of illness or complications in this setting is not clear.

These drugs can lead to complications. Confusion, delerium, seizures, falls, insomnia, or fractures occur in 22 to 47 percent of residents of LTCFs treated with amantidine, and drug resistance develops readily. Side effects can be reduced in the elderly by reducing the dose of amantadine to 100 mg or less daily in the presence of renal insufficiency. Central nervous system side effects are less problematic with rimantadine than with amantadine.

The neuraminidase inhibitors are a new class of antiviral medications with activity against both influenza A and B virus. These agents, although expensive, offer a much better side-effect profile and are better tolerated in the elderly than amantadine. Although resistance to these agents has been reported, it is not yet a significant problem. The role of these agents in the prevention and treatment of influenza infections in the elderly has not yet been established, but there is mounting evidence to suggest that they may play a key role in the management of influenza in LTCFs in the near future.

Prevention

Influenza vaccination represents the safest, most cost-effective means of prevention of morbidity and mortality from influenza virus. Current guidelines recommend influenza vaccine yearly in all individuals over age sixty-five, all residents of LTCFs, children or adults with chronic pulmonary or cardiovascular illness, children requiring chronic aspirin therapy, and women in the second or third trimester of pregnancy during influenza season. Yearly influenza vaccine is also recommended in health care workers, employees of LTCFs who come in contact with patients, and home care providers or others who have household contact with high-risk individuals.

At present, an inactivated vaccine directed at three viruses (influenza A H1N1, H3N2, and influenza B) is currently used. This vaccine can reduce the incidence of confirmed influenza, influenza-like illness, all respiratory infections, exacerbations of cardiopulmonary disease, hospitalization, and death in both community-dwelling elderly persons and in residents of LTCFs. Although the vaccine has only 30 to 40 percent efficacy in preventing influenza in residents of LTCFs, severe illness, hospitalization, and death are significantly reduced. High vaccination rates among residents of a LTCF significantly reduce the chances of an outbreak occurring in that facility, and should an outbreak occur, vaccination will decrease hospitalizations by 50 to 60 percent and mortality by as much as 80 percent. In order to maximize the effectiveness of the vaccine in the prevention of influenza-associated morbidity and mortality in residents of LTCFs, it is critical that high staff vaccine rates be maintained in hopes of reducing and delaying introduction of influenza into these facilities. A newly developed but not yet licensed cold-adapted, live, attenuated, trivalent, intranasal influenza vaccine has been shown to increase serum, mucosal, and cell-mediated immunity when given in combination with the currently available intramuscular vaccine.

Shelly McNeil

See also Lung, Aging; Pneumonia.

BIBLIOGRAPHY

Bradley, S. F., et al. "Prevention of Influenza in Long-Term Care Facilities." Infection Control Hospital Epidemiology 20 (1999): 629637.

Libow, L. S.; Neufeld, R. R.; Olson, E.; Breuer, B.; and Starer, P. "Sequential Outbreak of Influenza A and B in a Nursing Home: Efficacy of Vaccine and Amantidine." Journal of the American Geriatric Society 44 (1996): 11531157.

"Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices." Morbidity and Mortality Weekly Report 47 (1998): 116.

Treanor, J. J. "Influenza Virus." In Principles and Practices of Infectious Diseases, 5th ed. Edited by G. L. Mandell, J. E. Bennett, and R. Dolin. New York: Churchill Livingstone, 2000. Pages 18231849.

INSULIN

See Diabetes mellitus

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Influenza

Influenza

Influenza is a respiratory infection caused by a family of flu viruses. Often confused with either the common cold or stomach and intestinal infections, most forms of influenza are characterized by a sore throat, headache, chills, body aches, exhaustion, fever, and coughing. Droplets carried from one person to another by sneezing and coughing spread the disease, and touching can also contract it. According to the National Institutes of Health, the disease runs its course in about a week, and can be especially dangerous to infants and toddlers, the elderly, and those with compromised immune systems. Children acquire influenza easily, and can spread it to others rapidly. Normally, peaks of high wintertime reporting and low numbers of cases in the summer characterize influenza trends. Chances of acquiring an influenza infection during the flu season, usually November through March, increase with age, and pneumonia-influenza rates for those over seventy-five years old are much higher than for the middle-aged.

Influenza has annually ranked as one of the ten leading causes of death in the United States. During a typical flu season, anywhere from 35 to 50 million Americans could show symptoms of influenza. About 100,000 of those cases might be hospitalized, and as many as 20,000 could die from influenza and its complications. Influenza is also a substantial threat to human lives in many parts of the third world due to both a lack of effective vaccine distribution programs and a wide range of factors lowering resistance to many viruses.

Because a virus causes influenza, only specific symptoms and some ensuing infections can be treated with antibiotics. Primary prevention in the form of inoculation is the best method of combating influenza. Immunity to particular strains is acquired either naturally by previous exposure or induced with a vaccine, and the variants of influenza change over time. While there are broad categories of influenza A, B, and C that cause illness in humans, the A strains are by far the most lethal and hence the objective for focused vaccine development.

Some vaccines previously used are no longer effective because as the level of immunity in a population increases strains of influenza change genetically and propagate in those susceptible to the altered viral variants. The scholar W. I. B. Beveridge offers the explanation of how an influenza virus capsule has eight separate strands of ribonucleic acid (RNA) for its hereditary material. When a cell of a higher organism is infected by two different varieties of the virus, their sixteen RNA segments can combine to produce progeny with traits from both of the parent strains. New strains capable of evading the host's immunological defenses can thus emerge. Two of the eight viral genes code for protein-sugar complexes on the outer coat of the virus. These surface molecules, hemagglutinin (H) and neuraminidase (N), are antigens that can stimulate the host's immune system to make antibodies against the infecting virus. Subtypes H1, H2, H3, N1, and N2 are known to have caused human influenza epidemics and pandemics (worldwide epidemics) because of major shifts in the order of H and N antigens.

People have suffered from influenza for thousands of years. Written accounts date to the twelfth century, and the development of the printing press combined with changing worldwide travel patterns since the Age of Discovery created more knowledge about the disease. In his Diffision of Influenza (1986), the influenza researcher Gerald Pyle documents pandemics that took place in 1580, 17321733, 18001803, 18471848, and 18891892. These and similar events that transpired during the twentieth century are greatly overshadowed by the catastrophic pandemic of 19181919. It was so lethal that historians estimate that 40 million people were killed worldwide; a half million of them had been clearly documented in the United States. While the origins of this pandemic are unclear, it emerged from the trenches of World War I in an apocalyptic fashion, leaving a wake of deaths in diffusion pathways extending into most inhabited continents in the world.

Subsequent pandemics have been measured against this event, and although hundreds of thousands in the United States died during pandemics in 1957 and 1968, death tolls were far less than during the 19181919 episode. Since the 1950s, vaccine developments have kept pace with genetic shifts of influenza viruses. "Close calls" include a swine flu scare that was averted in 1976 and a contained outbreak of chicken flu in Hong Kong in 1997. According to Gina Kolata, researchers in the late 1990s uncovered the genetic makeup of the 19181919 virus from tissue samples stored in paraffin, but that mystery has intensified because the strain identified is unlike any other known influenza viruses. While the biological and geographic origins of the 19181919 pandemic remain unclear, it continues to serve as a landmark event in the annals of influenza.

See also: Causes of Death

Bibliography

Beveridge, W. I. B. "Unravelling the Ecology of Influenza A Virus." History, Philosophy, and Life Science 15 (1993):2332.

Kolata, Gina. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It. New York: Farrar, Straus and Giroux, 1999.

Patterson, K. David, and Gerald F. Pyle. "The Geography and Mortality of the 1918 Influenza Pandemic." Bulletin of the History of Medicine 65 (1991):421.

Pyle, Gerald. The Diffusion of Influenza: Patterns and Paradigms. Totowa, NJ: Rowman and Littlefield, 1986.

Internet Resources

National Institutes of Health, National Institute of Allergy and Infectious Diseases. "Fact Sheet: Flu." In the National Institute of Allergy and Infectious Diseases [web site]. Available from www.niaid.nih.gov/factsheets/flu.htm.

GERALD F. PYLE

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influenza

influenza or flu, acute, highly contagious disease caused by a RNA virus (family Orthomyxoviridae); formerly known as the grippe. There are three types of the virus, designated A, B, and C, but only types A and B cause more serious contagious infections. Influenza is difficult to diagnose in the absence of an epidemic, since it resembles many common respiratory ailments. It can be distinguished from a cold, however, by sudden fever, prostration, weakness, and sometimes severe muscular aches and pains. Stomach and intestinal symptoms, such as nausea and vomiting, are not commonly due to influenza infection, and the term stomach flu is a misnomer. Influenza is usually self-limiting, but complications such as pneumonia and bronchitis can be serious threats to newborns, the elderly, and people with chronic diseases. The viruses are spread by respiratory droplets, and the disease is typically most widespread from the late fall to early spring.

Vaccination is recommended for persons who are likely to be exposed to influenza (such as health-care workers) or who are at risk for complicatons. The antiviral drugs amantadine and rimantadine are effective against most strains of type A influenza, and zanamivir and oseltamivir against types A and B. Given within two days of the first appearance of symptoms, they may reduce the symptoms; they may also be given to prevent influenza infection in persons exposed to the disease. Uncomplicated influenza requires only rest and treatment of symptoms, and the use of antibiotics has greatly reduced fatalities from secondary infections. Return to normal activity should be undertaken slowly, as relapses are easily precipitated.

Serious influenza in humans is caused by strains of several A subtypes (which are designated by the specific combination of the 19 hemagglutinin and 9 neuraminidase proteins, or antigens, found on the virus's surface, e.g., H1N1) and by strains of type B. Type A is also found in swine, horses, whales, seals, and other animals, but wild birds are the only animals to have all A subtypes, and migratory birds can spread a strain of the disease great distances. Some H5 and H7 strains of avian influenza (also called avian flu or bird flu) are especially virulent and can result in financially devastating losses in the poultry industry. As a result, outbreaks of the disease are usually controlled by severe measures, including killing all poultry within a couple miles of the outbreak. Avian and swine influenza occasionally infect humans, but such cases rarely result in human-to-human transmission.

The influenza vaccine, which is based on the hemagglutinin and neuraminidase proteins, confers immunity only to the particular strain or set of strains including in the vaccine, and immunity to one strain or subtype, whether acquired through infection or vaccination, does not prevent susceptibility to another. Because the surface antigens of flu viruses change over time, it is necessary to reformulate the vaccine yearly in an educated guess at what strain will appear. (An influenza A vaccine that utilizes a surface protein that does not mutate is under development.) Abrupt major changes in a virus, which can result in increased virulence, also occur. Swine, which can be infected by avian and human influenzas, can facilitate such a development when avian and human strains are both present in an animal, enabling the genetic material of the two to reassort (mix). A major change can similarly occur in a person who is infected by both human and avian viruses.

Epidemics of influenza may be caused by type A or B strains, although type B is more likely to occur sporadically. Pandemics (worldwide epidemics) are caused only by type A. Three such pandemics occurred in the 20th cent., in 1918–19 (the "Spanish flu" ), 1957–58 (the "Asian flu" ), and 1968–69 (the "Hong Kong flu" ). In 1918–19, some 675,000 people died in the United States, and between 50 and 100 million died worldwide. Research suggests that the 1918–19 strain arose when an avian strain acquired the ability to infect humans, and the other two pandemics are known to have been caused by strains produced by the reassorting of human and avian viruses.

The avian strain A (H5N1), first known to have been transmitted directly to humans in 1997, began a new outbreak in several E Asian nations in 2003 and has shown increased virulence when transmitted to humans. International health officials are concerned that it could reassort with a human influenza virus, resulting in a new strain that would be both extremely virulent and highly contagious. By early 2006 the A (H5N1) outbreak had spread across Asia to birds and poultry in many European and some Africa nations. Some 600 cases of A (H5N1) influenza have been identified in humans, largely in Asia; roughly 60% of the cases have been fatal. Another avian strain, A (H7N9), infected humans with often deadly results in 2013–14; the strain, which first appeared in China, has been transmitted to humans mainly from poultry.

A new A (H1N1) strain of human influenza, containing genetic material from both swine, avian, and human influenzas but popularly known as swine flu, was detected in patients in Mexico in Apr., 2009, and rapidly spread worldwide, officially becoming pandemic by June, when at least 29,000 people in 74 nations had been infected, though many more uncounted cases were believed to have occurred. Apparently no more severe in most people than the normal seasonal flu, it nonetheless demonstrated how quickly a new strain to which many humans had little resistance could be spread around the globe, and by Nov., 2009, had become the dominant strain of human influenza worldwide. The outbreak was downgraded from pandemic status in Aug., 2010.

See G. Kolata, Flu (1999); A. W. Crosby, America's Forgotten Pandemic (2d ed. 2003); J. M. Barry, The Great Influenza (2004).

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Influenza

INFLUENZA

INFLUENZA, commonly called "the flu," reached America early in colonial history, and its periodic visitations have continued since then. John Eliot described the first epidemic, which struck in 1647, as "a very depe cold, with some tincture of a feaver and full of malignity.…" In the succeeding years a series of outbreaks, described in such terms as "a general catarrh," "winter feavers," "epidemical colds," and "putrid pleurisies," swept through the colonies, bringing death on a large scale. The cause of these epidemics remains unknown, but from accounts of the symptoms and the pandemic nature of the outbreaks, some strain of influenza is a logical suspect. Colonial records show many local outbreaks, with some form of respiratory disease reaching major epidemic proportions in


1675, 1688, 1732–1733, 1737, 1747–1750, 1761, and 1789–1791.

The nineteenth century saw a similar pattern of influenza epidemics—major pandemics interspersed with local or regional outbreaks. The disease spread through Europe and America in 1830, 1837, and 1847, eased up for a long period, and then broke out on a worldwide scale from 1889 to 1893.There were two minor outbreaks involving an unusual number of pneumonic complications in 1916 and 1917.In the summer of 1918, a deceptively mild wave of influenza swept through army camps in Europe and America, immediately followed by the second and third waves of the greatest recorded pandemic of influenza in history. In America the heaviest toll was exacted by a major wave lasting from September to November of 1918; the pandemic killed an estimated 15 million individuals worldwide. In the United States, the disease infected approximately 28 percent of the population, killing 450,000, with half of the deaths occurring among young adults between the ages of twenty and forty.

Several outbreaks struck in the 1920s, but the morbidity and mortality from influenza gradually declined in the succeeding years, although a Metropolitan Life Insurance Company study showed that influenza combined with pneumonia consistently remained the third-ranking cause of death among its policyholders as late as 1935.

Various forms of influenza have persisted; rarely do as many as three years go by without a fairly serious outbreak. Most occurrences are minor, but once or twice every decade the disease flares up. The introduction of new therapeutics in the 1940s led to a steady drop in the overall influenza mortality rate until the outbreaks of Asiatic influenza in 1957, 1958, and 1960.The influenza death rate per 100,000 reached 4.4 in the latter year, the last time this figure exceeded 4 per 100,000.

In 1933 the influenza virus now known as influenza virus A was identified, and other strains were later discovered. Although the impact of influenza vaccines has been limited, the introduction of sulfonamides, penicillin, and antibiotics in the World War II era greatly improved the treatment for pneumonia associated with influenza and thus helped reduce the fatality rate from influenza. Improved sanitary standards have also most likely helped reduce the number and virulence of influenza outbreaks.

BIBLIOGRAPHY

Bett, Walter R. The History and Conquest of Common Diseases. Norman: University of Oklahoma Press, 1954.

Crosby, Alfred W. America's Forgotten Pandemic: The Influenza of 1918. New York: Cambridge University Press, 1989.

Duffy, John. Epidemics in Colonial America. Baton Rouge: Louisiana State University Press, 1953.

Frost, W. H. "The Epidemiology of Influenza." Journal of the American Medical Association, 73 (1919): 313–318.

Kolata, Gina Bari. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus that Caused It. New York: Farrar, Straus and Giroux, 1999.

JohnDuffy/c. w.

See alsoCenters for Disease Control and Prevention ; Epidemics and Public Health ; Microbiology .

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Influenza

INFLUENZA

DEFINITION


Influenza is a highly infectious disease that affects the respiratory (breathing) tract. It is also known as the flu or grippe. The disease is caused by a virus. When inhaled, the virus attacks cells in the upper part of the respiratory system and causes symptoms such as fatigue, fever and chills, a hacking cough, and body aches. Influenza can also lead to other, more serious infections.

The disease known as stomach flu is not really a form of influenza. The influenza virus normally does not attack the stomach or intestines. Stomach flu is instead caused by other organisms, such as the salmonella or E. coli bacteria.

DESCRIPTION


The flu is often confused with the common cold (see common cold entry), but it is actually much more serious. The annual death toll due to influenza and its complications averages twenty thousand in the United States alone. Sometimes, a flu epidemic sweeps across a wide part of the world, killing large numbers of people. An epidemic is a sudden, rapid spread of a disease through a large geographical area. In 191819, a form of influenza known as the Spanish flu spread throughout the world. The death toll from the epidemic was estimated at twenty million to forty million people. About five hundred thousand of those deaths occurred in the United States.

Influenza: Words to Know

Common cold:
A mild infection of the upper respiratory tract caused by viruses.
Epidemic:
A widespread outbreak of a disease.
Reye's syndrome:
A potentially fatal illness in children believed to be associated with the use of aspirin.

Influenza outbreaks occur on a regular basis. An influenza epidemic occurred in 1957 and again in 1968. The first of these outbreaks was known as the Asian flu. The second was called the Hong Kong flu. About seventy thousand Americans died of the Asian flu and about thirty-four thousand from the Hong Kong flu.

Influenza has been known for more than 2,500 years. The ancient Greek physician Hippocrates was one of the earliest writers to describe the condition. Throughout most of history, people blamed the disease on a number of factors, including various kinds of bacteria and "bad air." In 1933, however, researchers found the real cause of the disease: a virus.

Three types of influenza viruses have now been discovered: types A, B, and C. Type A virus can infect many different kinds of animals, including humans, pigs, horses, and birds. Viruses B and C infect only humans. Influenza A is responsible for most cases of the disease in humans. Types B and C are less common and produce a milder form of infection.

CAUSES


Influenza is caused by the transmission of a flu virus from an infected person to an uninfected person. The virus can be transmitted by sneezing, coughing, sharing of eating and drinking utensils, and direct contact.

SYMPTOMS


The first symptoms of infection appear one to four days after the virus has entered a person's body. They include headache, dry cough, and chills. These symptoms are followed quickly by overall achiness and a fever that may run as high as 104°F (40°C). As the fever declines, nasal (nose) congestion and a sore throat become noticeable. The flu leaves an individual very tired and weak. A person with the flu may not return to normal for several days or even a few weeks.

A flu infection often leads to more serious complications. These complications are often caused by bacteria that get into the lower respiratory tract. The signs of a secondary (follow-up) infection often appear just as the person seems to be recovering from the flu. These signs include a high fever, chills, chest pains, and a cough that produces a thick, yellowish sputum (discharge from the throat). If these symptoms appear, medical treatment should be sought.

Secondary infections also affect the sinus or ears. The flu can also worsen heart and lung problems and certain other chronic diseases. For this reason, an attack of the flu can be especially serious for elderly people.

DIAGNOSIS


The symptoms of a flu infection are familiar to all medical workers. Doctors and nurses can usually diagnose the disease simply by examining a patient. Tests are available to identify the flu virus and the various forms in which it occurs, but these tests are seldom needed for the purpose of diagnosis. Some tests may be necessary to diagnose secondary infections. For example, a doctor may take a throat culture to identify a throat infection.

TREATMENT


Influenza cannot be cured. The usual course of action is to allow the body to heal itself. Various treatments are available to help relieve symptoms, however. For example, a person should get plenty of bed rest and drink lots of fluids. A steam vaporizer can make breathing easier. Painkillers help relieve the aches and pains of the flu. Children should not be given aspirin, however. Aspirin has been shown to cause a rare condition known as Reye's syndrome (see Reye's syndrome entry), which can be fatal.

Flu patients often do not feel hungry. However, they should be encouraged to eat as normally as possible. Patients should not try to return to normal activities too soon. Overactivity can cause a return of the infection or secondary infections.

Drugs

Patients sometimes ask their doctor for antibiotics to cure the flu. But antibiotics have no effect on the flu virus. They can be used, however, to treat secondary infections.

There are many over-the-counter (nonprescription) medications for the treatment of flu symptoms. Medications that include alcohol should be avoided, however. Alcohol has a tendency to reduce the amount of water in a person's body. The best medicine is often an analgesic (painkiller), such as acetaminophen (pronounced uh-see-tuh-MIN-uh-fuhn, trade name Tylenol) or naproxen (pronounced nuh-PROKS-suhn, trade name Aleve).

Two antiviral drugs are available for the treatment of influenza in the United States. They are recommended for people with weak immune systems or people who are allergic to the flu vaccine. These two drugs are amantadine hydrochloride (pronounced uh-MANT-uh-deen HIE-druh-KLOR-ide, trade names Symmetrel, Symadine, Amantadine-hydrochloride) and rimantadine hydrochloride (pronounced ruh-MAN-tuh-deen HIE-druh-KLOR-ide, trade name Flumandine). Both drugs are effective against type A viruses only. These should be used with care because they both have serious side effects.

Alternative Treatment

A number of alternative treatments have been recommended for the treatment of influenza. In most cases, there is little scientific evidence for the success of these treatments.

  • Acupuncture and acupressure. Practitioners believe that these two techniques can stimulate natural resistance, relieve nasal congestion and headaches, reduce fever, and soothe coughs. Acupuncture is a Chinese therapy that uses fine needles to pierce the body; acupressure involves applying pressure to certain points in the body.
  • Aromatherapy. Aromatherapists recommend gargling daily with one drop each of tea tree oil and lemon in a glass of warm water. Two drops of tea tree oil in a hot bath may help ease some symptoms. A few drops of the oils of eucalyptus (pronounced yoo-kuh-LIP-tus) or peppermint can be added to a steam vaporizer. They may help clear chest and nasal congestion.
  • Herbal remedies. Echinacea (pronounced ek-i-NAY-see-uh) has been recommended to improve a person's immune system. Certain herbs, such as goldenseal and garlic, are thought to be able to kill viruses. A number of herbs can be used to treat the symptoms of influenza. For example, boneset may counteract aches and fever, and yarrow or elder flower may combat chills.
  • Homeopathy. Homeopathic practitioners recommend a variety of herbs to treat the symptoms of the flu. These include Gelsemium (pronounced jel-SEE-mee-uhm) for the treatment of chills, headache, and nasal congestion; Bryonia (pronounced brie-OH-nee-uh) for muscle aches, headaches, and dry cough; and poison ivy for restlessness, chills, hoarseness, and achy joints.
  • Hydrotherapy. Taking a hot bath may help a person recover from the flu more quickly: The higher a person's body temperature, the more quickly the virus is likely to die. Hydrotherapists recommend that a person drink a cup of yarrow or elder flower tea while taking a bath: These herbs cause a person to sweat.
  • Vitamins. Some people believe that large doses of vitamin C can help prevent the flu. They suggest increasing the amount of vitamin C once a flu infection has started.

PROGNOSIS


Healthy people under the age of sixty-five seldom experience serious, long-term consequences from a flu infection. Older people and people who are chronically ill are at risk for secondary infections, but they often recover from the flu quickly and completely. The high recovery rate from influenza should not be misleading. The infection can still be very serious. About 1 in 1,000 cases will actually lead to the patient's death.

PREVENTION


Vaccines are now available to help prevent influenza infections. The composition of these vaccines is changed every year. A vaccine is designed to protect people against three specific influenza virusesthe viruses thought to be most likely to infect people in a given year. Scientists may or may not make good guesses as to the "most likely" flu viruses. When they are successful, the vaccine can be 70 percent to 90 percent effective in people under the age of sixty-five.

The U.S. Centers for Disease Control and Prevention recommend that people get a flu vaccine injection each year before the flu season starts. In the United States, flu season usually runs from late December to early March. Adults usually need only one dose of the vaccine. Children under the age of nine who have not previously been vaccinated will need two doses one month apart.

Side effects from influenza vaccinations are rare. People who have never had influenza may experience about two days of discomfort. They may have a slight fever, feel tired, and experience achy muscles.

Certain people should not have influenza vaccinations. They include infants under the age of six months and people who are allergic to eggs. These people can be given the antiviral drugs described if necessary. However, certain groups of people are strongly advised to be vaccinated. These groups include:

  • All people over the age of sixty-five
  • Residents of nursing homes and other health-care facilities, regardless of age
  • Adults and children who have chronic heart or lung problems, such as asthma (see asthma entry)
  • Adults and children who have other kinds of chronic diseases, such as diabetes (see diabetes mellitus entry), severe anemia (see anemias entry), blood disorders, or kidney problems
  • Children and teenagers who are on long-term aspirin therapy
  • Women who are in the last two-thirds of their pregnancy and women who are nursing
  • People with weakened immune systems, such as AIDS patients (see AIDS entry), people who have received organ transplants, and patients receiving various types of medical treatments, such as chemotherapy or radiation therapy
  • Anyone who has regular contact with people in any of the above groups, such as teachers, health-care personnel, and family members
  • Travelers to foreign countries

An individual need not be in one of the at-risk groups to receive a flu vaccination. Anyone who wants to avoid the discomfort of an influenza attack may receive the vaccine.

FOR MORE INFORMATION


Books

Brody, Jane E. Jane Brody's Cold and Flu Fighter. New York: W. W. Norton & Company, 1995.

Inlander, Charles B., and Cynthia K. Moran. 77 Ways to Beat Colds and Flu. New York: Walker & Company, 1994.

Silverstein, Alvin, Virginia Silverstein, and Robert Silverstein. Common Cold and Flu. Hillside, NJ: Enslow Publishers, Inc., 1994.

Periodicals

Novitt-Moren, Anne. "Holiday's Biggest Spoilers: Colds and Flu." Current Health (December 1997): p. 6.

Saul, Helen. "Flu Vaccines Wanted: Dead or Alive." New Scientist (February 18, 1995): p. 26.

Organizations

Centers for Disease Control and Prevention. 1600 Clifton Road NE, Atlanta, GA 30333. (888) CDC-FACTS. http://www.cdc.gov.

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influenza

influenza (in-floo-en-ză) n. a highly contagious virus infection that affects the respiratory system; types A and B are the forms that most commonly cause outbreaks in humans. Symptoms include headache, fever, loss of appetite, weakness, and general aches and pains. With bed rest and aspirin most patients recover, but a few go on to develop viral or bacterial pneumonia. avian i. a disease of poultry and other birds caused by influenza A viruses, some strains of which have been transmitted to humans to cause outbreaks of influenza with a high mortality rate. See H5N1.

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Influenza

Influenza

What Is Influenza?

How Common Is Influenza?

How Do People Know They Have the Flu?

How Is Influenza Diagnosed and Treated?

Can the Flu Be Prevented?

Resources

Influenza (in-floo-EN-zuh), also known as the flu, is a contagious viral infection that attacks the respiratory tract, including the nose, throat, and lungs.

KEYWORDS

for searching the Internet and other reference sources

Pandemic

Respiratory infection

Spanish flu

Vaccination

Viral infection

What Is Influenza?

The respiratory infection influenza, commonly known as the flu, causes symptoms that include fever, muscle aches, sore throat, and a cough. Once inhaled, flu germs quickly multiply and take over healthy cells. In its early stages, influenza sometimes is confused with the common cold because both affect similar body parts, but the flu is more severe, lasts longer, and can cause dangerous complications.

Flu viruses come in three varieties: types A, B, and C. Types A and B cause large flu outbreaks or epidemics* each year, whereas the less common Type C flu virus causes only mild symptoms. Usually, if people have been infected by a virus or are vaccinated against the virus, their bodies build up immunity* that defends them from being infected by that particular virus again. Flu viruses, however, can cause epidemics because

*epidemics
(eh-pih-DEH-miks) are outbreaks of diseases, especially infectious diseases, in which the number of cases suddenly becomes far greater than usual. Usually, epidemics that involve worldwide outbreaks are called pandemics.
*immunity
(ih-MYOON-uh-tee) is the condition of being protected against an infectious disease. Immunity often develops after a germ is introduced to the body. One type of immunity occurs when the body makes special protein molecules called antibodies to fight the disease-causing germ. The next time that germ enters the body, the antibodies quickly attack it, usually preventing the germ from causing disease.

Cases of influenza virus infection typically peak in the fall and winter and decrease in the warmer months. During the 1918 pandemic, the virus killed more than 33,000 people in New York City alone, just over 1% of the citys population.

they have the ability to mutate (change) so that new strains of viruses appear regularly. This is why people who are at risk for complications of flu need to get a flu vaccination every year.

How Common Is Influenza?

Millions of Americans of all ages contract the flu each year, but the people most at risk of severe illness are people over 65 years of age, children under age 5, and anyone with a serious medical condition. Flu season is November through April in the United States.

Influenza is extremely contagious, mostly because people (especially school children) often spread it before they even know that they are sick. Also, those with the infection usually remain contagious for about a week after first showing symptoms.

When an infected person sneezes, coughs, or talks too closely to others, the flu virus is passed through tiny drops of fluid that are launched into the air and can be breathed in by someone else. The virus can also be left on surfaces that a person with the flu has touched, such as doorknobs, desks, and keyboards, so people who forget to wash their hands after touching these things can easily become infected by rubbing their eyes or touching their mouth.

How Do People Know They Have the Flu?

Flu symptoms are usually worse than those seen with a cold. Symptoms include:

  • sneezing, runny nose, and congestion (stuffed-up nose)
  • high fever
  • headache
  • chills
  • dry-sounding cough
  • muscle aches
  • abdominal* pain and poor appetite
*abdominal
(ab-DAH-mih-nul) refers to the area of the body below the ribs and above the hips that contains the stomach, intestines, and other organs.
  • tiredness

What Is the Stomach Flu?

When people complain about the stomach flu, what they actually are describing is gastroenteritis (gas-tro-en-ter-EYE-tis). The stomach cramps, nausea, and vomiting that accompany a bout of gastroenteritis usually only last a day or two and are different from the group of symptoms seen with influenza virus infection.

Most people have symptoms of the flu for 7 to 14 days. The high fever and body aches usually disappear within a few days, but those symptoms may be quickly replaced by a sore throat, runny nose, and lingering cough. In some cases, fever may even return for a brief period. Feelings of tiredness and exhaustion can last several days or weeks in some people with the flu. Trying to return to a normal routine too quickly can cause symptoms, especially exhaustion, to reoccur.

Sometimes people with the flu develop bronchitis* or pneumonia*. Pneumonia can be a serious complication of the flu. It usually occurs when bacteria infect lung tissue that is already inflamed by the flu virus. This complication can be life threatening in young infants and in elderly people. Influenza can also worsen the symptoms of other common heart and lung diseases, such as congestive heart failure, chronic* bronchitis, and asthma*.

*bronchitis
(brong-KYE-tis) is a disease that involves inflammation of the larger airways in the respiratory tract, which can result from infection or other causes.
*pneumonia
(nu-MO-nyah) is inflammation of the lung.
*chronic
(KRAH-nik) means continuing for a long period of time.
*asthma
(AZ-mah) is a condition in which the airways of the lungs repeatedly become narrowed and inflamed, causing breathing difficulty.

The flu can knock even the healthiest people off their feet for a couple of weeks. Most people recover with time and rest, but for some people with chronic medical conditions, the flu can pose a severe health risk and can even be deadly. Hundreds of thousands of Americans are hospitalized every year due to the virus, and about 20,000 die from the flu or its complications.

Because the flu can go from bad to worse very quickly, doctors recommend that people with the flu seek medical care immediately if they experience any of the following:

Flu on the Front Lines

In 1918, the world was blindsided by the most catastrophic flu outbreak of all time. In the midst of World War I, the flu virus spread to nations around the globe through soldiers traveling by boat or gathering in trenches. In less than 2 years, the flu killed over 20 million people worldwide. This pandemic (a worldwide outbreak of disease) came to be known as the Spanish Flu because Spain lost the most people to the deadly infection, nearly 8 million.

  • a fever that lasts longer than 5 days
  • any breathing difficulty, including wheezing (WEE-zing), a whistling sound that occurs while breathing or coughing
  • a continuous cough that makes it difficult to breathe
  • a cough that brings up blood or thick green or dark yellow mucus

Soups on!

It turns out that Moms chicken soup does more than just warm you up. The steamy soup naturally clears congestion and relieves stuffy noses and dry coughs. Researchers also have discovered that compounds found in chicken soup slow down the activity of the white blood cells that cause inflammation (and discomfort) in the respiratory tract during an infection.

How Is Influenza Diagnosed and Treated?

To diagnose the flu, a doctor performs a physical examination and asks the patient questions about symptoms to find out if influenza is the culprit or if a cold or another kind of respiratory problem is to blame. A small cotton swab may be used to collect some of the fluid from the back of the nose. This fluid sample can then be tested to see if the flu virus is present. The doctor also will make sure that the person is not experiencing any complications of the flu, such as bronchitis or pneumonia.

Like all viral infections, the flu will not respond to antibiotics, although in some cases they may be helpful for treating bacterial infections, such as pneumonia, that can occur as complications of the flu. The best medicine for the flu is lots of rest. Taking an over-the-counter, non-aspirin medication such as acetaminophen (uh-see-teh-MIH-noh-fen) to ease fever and muscle aches, drinking plenty of liquids, and using a humidifier to keep the air cool, moist, and easier to breathe can help people with the flu feel better as they recover.

Occasionally, doctors will prescribe antiviral flu medications, such as amantadine (uh-MAN-ta-deen) or rimantadine (rih-MAN-tuh-deen). These medications do not offer a cure but can reduce the length and severity of the illness. They must be taken within 48 hours of the start of flu symptoms in order to work.

Can the Flu Be Prevented?

Getting a flu shot can help prevent a person from contracting some strains of the flu. The vaccine contains particles from killed influenza viruses of the types expected to cause flu outbreaks during the upcoming season. After the shot, the body builds up a defense against these particular influenza virus strains. Although the flu shot does not guarantee that a person will not contract the flu, it does reduce the chance of becoming sick by 80 to 90 percent. Despite popular belief, the flu shot cannot give a person the flu. The elderly, people with certain heart and lung diseases, and workers in places such as hospitals, schools, and daycare centers should get a flu shot every year before the flu season begins in November. More recently, flu vaccination has been recommended for infants and children from age 6 months to 2 years because children in this age group are at high risk for respiratory complications of the flu.

Because the highly contagious flu virus is easily passed from person to person through the air, the virus can be lurking almost anywhere. Experts recommend that hands be washed thoroughly with warm, soapy water for at least 15 to 30 seconds after using a public restroom and before eating or touching the face.

Avoiding contact with people who have the flu can also lower the risk of catching it. By avoiding close contact in large crowds, especially at schools or in malls, and by not touching used tissues or sharing drinks, a person can reduce the chance of becoming sick.

See also

Bronchitis, Infectious

Common Cold

Laryngitis

Pneumonia

Vaccination (Immunization)

Resources

Organization

American Lung Association, 61 Broadway, 6th floor, New York, NY 10006. The American Lung Association offers guidelines on its website for the treatment and prevention of influenza.

Telephone 212-315-8700 http://www.lungusa.org

Website

KidsHealth.org. KidsHealth is a website created by the medical experts of the Nemours Foundation and is devoted to issues of childrens health. It contains articles on a variety of health topics, including influenza. http://www.KidsHealth.org

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influenza

in·flu·en·za / ˌinfloōˈenzə/ • n. a highly contagious viral infection of the respiratory passages causing fever, severe aching, and catarrh, and often occurring in epidemics. Also called flu. DERIVATIVES: in·flu·en·zal adj.

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influenza

influenza Viral infection mainly affecting the airways, with chesty symptoms, headache, joint pains, fever and general malaise. It is treated by bed-rest and pain-killers. Vaccines are available to confer immunity to some strains.

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influenza

influenza XVIII. — It. influenza INFLUENCE, used spec. for visitation or outbreak of an epidemic (e.g. influenza di catarro, influenza di febbre scarlattina), hence absol. epidemic.

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influenza

influenzaBalthazar, Belshazzar, jazzer •bonanza, Braganza, Constanza, extravaganza, kwanza, organza, Panzer, stanza •parser, plaza, tabula rasa •Shevardnadze • dopiaza •Nebuchadnezzar • Demelza •cadenza, cleanser, credenza, influenza, Penza •appraiser, blazer, eraser, Fraser, gazer, glazer, grazer, laser, mazer, praiser, razor, salmanazar, Weser •stargazer • trailblazer • hellraiser •appeaser, Caesar, easer, Ebenezer, El Giza, freezer, geezer, geyser, Louisa, Pisa, seizer, squeezer, teaser, Teresa, Theresa, visa, wheezer •crowd-pleaser • stripteaser •fizzer, quizzer, scissor •Windsor

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Influenza

Influenza

Resources

Influenza (commonly called the flu) is an infectious disease caused by the influenza virus. The disease is easily spread from person to person, typically by inhaling virus that has been expelled into the air by

coughing or sneezing. The virus can also be spread by touch. For example, if someone touches a doorknob that has influenza viruses clinging to it and then touches their mouth, the virus can pass into their body and cause influenza.

The influenza virus infects the nose, throat, and lungs of people. In contrast to the common cold, which is caused by a different virus, the symptoms of the flu develop suddenly. These symptoms include fever, headache and body aches, tiredness, cough, sore throat, and stuffy nose. The incubation period for influenza is shortbetween one and three daysand the first symptom is a fever that may reach 103°F (39.4;°C). Cough and gastrointestinal discomfort may also accompany the disease. Usually, the viral infection runs its course in about a week. However, the virus weakens the immune system, making the human body subject to secondary infections such as bacterial pneumonia. Fatalities associated with influenza usually result from such secondary complications. The presence of viral pneumonia was probably the cause of many deaths during the great influenza epidemics of the past.

Most people who contract the flu recover completely in a few weeks. However, in some people influenza can progress to pneumonia, which can be life threatening. Recovery from influenza does not protect someone from future bouts of the disease. This is because the influenza virus readily changes the expressions of its genetic material (i.e., it mutates readily). Thus, the influenza virus that the bodys immune system responds to one season may be different from the virus that infects the body some months later.

Influenza is a common illness. For example, according to the U.S. Centers for Disease Control and Prevention (CDC) every year approximately 1560 million Americans (about 520% of the population of the United States, as of August 2006) contract influenza. Of these, about 36,000 people die of the infection, and over 200,000 people require hospitalization.

There are three types of influenza virus. All three are in the viral group called Orthomyxovirus. The three viral types are called influenza A, B, and C. Influenza A and B cause large numbers of cases of the flu almost every winter, when people are confined indoors and spread of the virus is easier.

Influenza A is further divided into two subtypes called hemagglutinin (H) and neuraminidase (N). H and N are two proteins that are found on the surface of the filament-like virus particles. They both protrude from the surface and appear as spikes when viruses are examined under high magnification. The protein spikes function to help the virus invade host cells.

Influenza viruses are resident in animals and birds including pigs, horses, seals, whales, a variety of wild birds, and ducks. The virus can spread from this reservoir to humans.

Influenza has been part of humankind for millennia. Historically, influenza has been known for centuries and may have been what Ancient Greek physician Hippocrates of Cos (c. 460370 BC) described as the cause of an epidemic as early as 412 BC. In the twentieth century, there were a number of large outbreaks. For example, in 19181919 the Spanish flu killed more than 500,000 people in the United States and up to 50 million people around the world. The influenza virus that caused this outbreak was very deadly. Concerns have been raised that the same virus could establish another epidemic.

Not until the 1930s with the invention of more powerful microscopes did scientists began to see pathogens much smaller than bacteriawhat today are called viruses. During that decade, the nature of viruses was discovered. Wendell M. Stanley (19041971), an American biochemist, prepared large quantities of viruses, and found that they could be crystallized. Viruses are very simple structures made of only proteins and nucleic acids that could be crystallized in much the same way as other nonliving chemicals. However, when a virus is inside a living cell it uses the cells genetic machinery to make more copies of itself. Stanley had discovered that viruses are on the borderline between living and nonliving things because they grow only when inside living cells. During World War II, Stanley worked on culturing the influenza virus.

In 1957 to 1958 the Asian flu caused 70,000 deaths in the United States. The same virus remains in circulation today. In 1968 to 1969, an outbreak of what was dubbed the Hong Kong flu killed approximately 34,000 Americans. In 1976, a small outbreak affected soldiers at a military base in Fort Dix, New Jersey. Experts predicted that the influenza, which was known as the Swine flu, could spread throughout the United States. The subsequent public concern bordered on hysteria, and prompted a vaccination campaign in which 40 million Americans were vaccinated. The outbreak did not materialize.

In 1997 a three-year-old boy in Hong Kong died from a virus previously thought to occur only in birds. Investigators believe that the transmission was direct from bird to human without the usual intermediary pig. Prior to the boys infection, thousands of chickens in Hong Kong died from the virus. By the end of 1997, 15 additional cases had occurred in the city.

Research has shown that viruses have a phenomenal ability to change, or mutate, very quickly. A treatment that may have worked on one flu virus may not work on another. Each year different strains develop. They are named for places where they first occurred.

From late 2003 to 2006, outbreaks of avian influenza H5N1 occurred in poultry in many countries in Asia. Over 100 million birds were killed or died from the disease. Although thought to be under control in March 2004, it resurfaced again in June/July 2004. Since December 2003, several cases have been reported in humans, mostly from direct or close contact with infected poultry or contaminated surfaces. Experts from around the world are closely watching the H5N1 virus, now commonly called (simply) the avian flu. Governments such as the United States are preparing for the possibility that the avian flu may begin to spread quickly from human-to-human, resulting in a possible influenza pandemic, or a worldwide outbreak.

Vaccination is not a guarantee that all types of influenza will be prevented. Rather, influenza is typically dealt with after it appears. Flu is treated with rest and fluids. Maintaining a high fluid intake is important, because fluids increase the flow of respiratory secretions that may prevent pneumonia. Antiviral medications such as amantadine and rimantadine may be prescribed for people who have initial symptoms of the flu and who are at high risk for complications. This medication does not prevent the illness, but reduces its duration and severity.

A flu vaccine is available that is formulated each year against the current type and strain of flu virus. The virus is grown in chicken eggs, extracted, and, then, rendered noninfective by chemicals. The vaccine is also updated to the current viral strain by the addition of proteins that match the protein composition of the influenza virus type that is currently circulating in a population. The vaccine would be most effective in reducing attack rates if it was effective in preventing influenza in schoolchildren; however, in vaccine trials the vaccine has not been shown to be effective in flu prevention in this age group. In certain populations, particularly the elderly, the vaccine is effective in preventing serious complications of influenza and thus, lowers mortality.

Vaccine research is ongoing. One of the more exciting advances in flu vaccines involves research studies examining an influenza vaccine mist, which is sprayed into the nose. This is predicted to be an excellent route of administration, which will confer even stronger immunity against influenza. Because it uses a live virus, it encourages a strong immune response. Furthermore, it is thought to be a more acceptable immunization route for schoolchildren, who are an important reservoir of the influenza virus.

Resources

BOOKS

Kolata, G.B. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It. New York: Farrar Straus & Giroux, 1999.

Potter, C.W. Influenza London: Elsevier Health Sciences, 2002.

OTHER

Centers for Disease Control and Prevention. <http://www.cdc.gov/ncidod/diseases/flu/fluinfo.htm> (October 11, 2006).

Brian Hoyle

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Influenza

Influenza

Influenza (commonly known as flu) is a highly contagious illness caused by a group of viruses called the orthomyxoviruses. Infection with these viruses leads to a self-limiting illness usually characterized by fever, muscle aches, fatigue, and upper respiratory infection and inflammation . Children and young adults usually recover from influenza within 37 days with no complications; however, in older adults, especially those over 65 with underlying conditions such as heart disease or lung illnesses, influenza can be deadly. Most of the hospitalizations and deaths from influenza occur in this age group. Although an influenza vaccine is available, it does not confer complete protection against all strains of influenza viruses.

Like all viruses, orthomyxoviruses cause illness by entering host cells and replicating within them. The new viruses then burst from the host cell and infect other cells. Orthomyxoviruses are sphere-shaped viruses that contain ribonucleic acid (RNA ). The viruses use this RNA as a blue-print for replication within host cells. The outer envelope of an orthomyxovirus is studded with protein spikes that help the virus invade host cells. Two different types of spikes are present on the virus's outer envelope. One type, composed of hemagglutinin protein (HA), fuses with the host cell membrane, allowing the virus particle to enter the cell. The other type of spike, composed of the protein neuraminidase (NA), helps the newly formed virus particles to bud out from the host cell membrane.

The only way a virus can be neutralized and stopped is through the body's immune response. At the present time, no cure or treatment is available that completely destroys viruses within the body. The HA spikes and proteins in the orthomyxovirus envelope stimulate the production of antibodies, immune proteins that mark infected cells for destruction by other immune cells. In a healthy person, it takes about three days for antibodies to be formed against an invading virus. People with impaired immune function (such as people with Acquired Immune Deficiency Syndrome, the elderly, or people with underlying conditions) may not be able to mount an effective immune response to the influenza virus. Therefore, these people may develop serious complications, such as pneumonia , that may lead to hospitalization or death.

Three types of orthomyxoviruses cause illness in humans and animals: types A, B, and C. Type A causes epidemic influenza, in which large numbers of people become infected during a short period of time. Flu epidemics caused by Type A orthomyxoviruses include the worldwide outbreaks of 1918, 1957, 1968, and 1977. Type A viruses infect both humans and animals and usually originate in the Far East, where a large population of ducks and swine incubate the virus and pass it to humans. The Far East also has a very large human population that provides a fertile ground for viral replication. In 1997, a new strain of influenza A jumped from the poultry population in Hong Kong to the human population. H5N1, as the strain was named, was contracted through contact with the feces of chicken. The illness it caused (dubbed avian flu) was severe, and sometimes fatal. Although it was strongly believed that humans could not get the disease from eating properly cooked chicken, the decision was ultimately made to destroy and bury all of the chickens in Hong Kong. This massive effort was carried out in December 1997.

Type B influenza viruses are not as common as type A viruses. Type B viruses cause outbreaks of influenza about every two to four years. Type C viruses are the least common type of influenza virus and cause sporadic and milder infections.

The hallmark of all three kinds of influenza viruses is that they frequently mutate. Due to the small amount of RNA genetic material within a virus, mutation of the genetic material is very common. The result of this frequent mutation is that each flu virus is different, and people who have become immune to one flu virus are not immune to other flu viruses. The ability to mutate frequently therefore allows these viruses to cause frequent outbreaks.

Influenza is characterized by a sudden onset of fever, cough, and malaise. The incubation period of influenza is short, only 13 days. The cells that the influenza virus target are the cells of the upper respiratory tract, including the sinuses, bronchi, and alveoli. The targeting of the upper respiratory tract by the viruses accounts for the prominence of respiratory symptoms of flu. In fact, flu viruses are rarely found outside the respiratory tract. Most of the generalized symptoms of flu, such as muscle aches, are probably due to toxin-like substances produced by the virus.

Symptoms last for about 36 days; however, lethargy and cough may persist for several days to weeks after a bout with the flu. Children may have more severe symptoms due to a lack of general immunity to influenza viruses. Children also have smaller airways, and thus may not be as able to compensate for respiratory impairment as well as adults.

The most common complication of influenza is pneumonia. Pneumonia may be viral or bacterial. The viral form of pneumonia that occurs with influenza can be very severe. This form of pneumonia has a high mortality rate. Another form of pneumonia that is seen with influenza is a bacterial pneumonia. If the respiratory system becomes severely obstructed during influenza, bacteria may accumulate in the lungs. This type of pneumonia occurs 510 days after onset of the flu. Because it is bacterial in origin, it can be treated with antibiotics .

Other complications of influenza include infections of the heart and heart lining, infections of the brain, and Guillain-Barre syndrome (GBS). GBS is a paralytic disease in which the body slowly becomes paralyzed. Paralysis starts in the facial muscles and moves downward. GBS is treated symptomatically and usually resolves by itself. Another complication of influenza is Reye's syndrome. Occurring typically in children, Reye's syndrome is associated with aspirin intake during an attack of influenza. Reye's syndrome is characterized by nausea, vomiting, and progressive neurological dysfunction. Because of the risk of Reye's syndrome, children should not be given aspirin if they have the flu. Non-aspirin pain relievers, such as acetaminophen, should be given instead of aspirin.

Flu is treated with rest and fluids. Maintaining a high fluid intake is important, because fluids increase the flow of respiratory secretions, which may prevent pneumonia. Antiviral medications (amantadine, rimantadine) may be prescribed for people who have initial symptoms of the flu and who are at high risk for complications. This medication does not prevent the illness, but reduces its duration and severity.

A flu vaccine is available that is formulated each year against the current type and strain of flu virus. The virus is grown in chicken eggs, extracted, and then rendered noninfective by chemicals. The vaccine is also updated to the current viral strain by the addition of proteins that match the current strain's composition. The vaccine would be most effective in reducing attack rates if it was effective in preventing influenza in schoolchildren; however, in vaccine trials the vaccine has not been shown to be effective in flu prevention in this age group. In certain populations, particularly the elderly, the vaccine is effective in preventing serious complications of influenza and thus lowers mortality.

Vaccine research is ongoing. One of the more exciting advances in flu vaccines involves research studies examining an influenza vaccine mist, which is sprayed into the nose. This is predicted to be an excellent route of administration, which will confer even stronger immunity against influenza. Because it uses a live virus, it encourages a strong immune response. Furthermore, it is thought to be a more acceptable immunization route for schoolchildren, an important reservoir of the influenza virus.

See also Flu: The great flu epidemic of 1918; Viruses and responses to viral infection

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Influenza

Influenza

Definition

Usually referred to as the flu or grippe, influenza is a highly infectious respiratory disease caused by certain strains of influenza virus. When the virus is inhaled it attacks cells in the upper respiratory tract causing typical flu symptoms such as fatigue, fever and chills, hacking cough, and body aches. Influenza victims are also susceptible to potentially life-threatening secondary infections. Although the stomach or intestinal upsets and diarrhea are commonly called "flu," the influenza virus rarely causes gastrointestinal symptoms. Such symptoms are most likely due to other organisms such as rotavirus, Salmonella, Shigella, or Escherichia coli.

Description

Influenza is considerably more debilitating than the common cold. Influenza outbreaks occur suddenly and infection rapidly spreads. The annual death toll attributable to influenza and its complications averages 20,000 in the United States alone.

Influenza outbreaks occur on a regular basis. Pandemics, the most serious outbreaks, affect millions of people worldwide and last for several months. The 1918–1919 influenza outbreak serves as the primary example of an influenza pandemic. In that Spanish flu pandemic, the death toll reached a staggering 20-40 million people worldwide. Approximately 500,000 of these fatalities occurred in the United States. Pandemics also occurred in 1957 and 1968 with the Asian flu and Hong Kong flu, respectively. The Asian flu was responsible for 70,000 deaths in the United States, while the Hong Kong flu killed 34,000 people.

Epidemics are widespread regional outbreaks that occur every two-to-three years and affect 5%-10% of the population. The Russian flu in the winter of 1977 is an example of an epidemic. A regional epidemic is shorter lived than a pandemic, lasting only several weeks. Finally, there are smaller outbreaks each winter that are confined to specific locales.

The earliest existing descriptions of influenza were written nearly 2,500 years ago by the ancient Greek physician, Hippocrates. Historically, influenza was ascribed to a number of different agents, including "bad air" and several different bacteria. It was not until 1933 that the causative agent was identified as a virus.

There are three types of influenza viruses, identified as A, B, and C. Influenza A can infect a range of species, including humans, pigs, horses, and birds, but only humans are infected by types B and C. Influenza A is responsible for most flu cases, while infection with types B and C viruses are less common and cause a milder illness.

Causes and symptoms

Approximately one to four days after infection with the influenza virus, a person is hit with an array of symptoms. "Hit" is an appropriate term, because symptoms are sudden, harsh, and followed by overall bodily aches and a fever that may run as high as 104°F (40°C). As the fever subsides, nasal congestion and a sore throat become noticeable. Persons with the flu feel extremely tired and generally miserable. Typical influenza symptoms include the abrupt onset of a headache, dry cough, and chills, and a rapid onset of physical weakness. Normal energy levels typically do not return for several days, but this can extend up to two weeks.

Influenza complications usually arise from secondary bacterial infections of the lower respiratory tract. Signs of a secondary respiratory infection often appear just as a person seems to be recovering. These signs include high fever, intense chills, chest pains associated with breathing, and a productive cough with thick, yellowish-green sputum. If these symptoms appear, medical treatment is necessary. Other secondary infections, such as sinus or ear infections, may also require medical intervention. Heart and lung problems and other chronic diseases can be aggravated by influenza. This is a particular concern among elderly people.

With children and teenagers, it is advisable to be alert for symptoms of Reye's syndrome, a rare but serious complication of the flu. Symptoms of Reye's syndrome are nausea and vomiting, and—more seriously—neurological problems such as confusion or delirium. Among children Reye's syndrome can be fatal. The syndrome has been associated with the use of aspirin to relieve flu symptoms.

Diagnosis

Although specific laboratory tests can be performed on respiratory samples to identify a flu virus strain, doctors typically rely on a set of symptoms and the presence of influenza in the community for diagnosis. Specific tests are useful to determine the type of flu in the community, but they do little to influence individual treatment. Doctors may administer tests, such as throat cultures, to identify and treat secondary bacterial infections.

Treatment

Essentially, little can be done for a case of influenza an it must simply run its course. Symptoms can be relieved with bed rest and by keeping well hydrated. A steam vaporizer may make breathing easier, and pain relievers such as ibuprofen and acetaminophen will relieve most aches and pains. Food may not seem appetizing, but an effort should be made to consume nourishing food. Returning to normal activities too quickly invites a possible relapse or complications.

Drugs

Since influenza is a viral infection, antibiotics are not an effective treatment. However, antibiotics are frequently used to treat secondary infections. Over-the-counter medications are used to treat symptoms, but it is not necessary to purchase a product marketed specifically for flu symptoms. Any medication designed to relieve pain and coughing will provide some relief. Products containing alcohol, however, should be avoided because of the dehydrating effects of alcohol. The best medicine for symptoms is simply an analgesic, such as acetaminophen or ibuprofen. Without a doctor's approval, aspirin is generally not recommended for people under the age of 18 years owing to its association with Reye's syndrome. As a precaution against the syndrome, children should receive acetaminophen or ibuprofen to treat their symptoms.

There are two antiviral drugs marketed for use in the United States against the influenza virus. These may be useful in treating individuals who have weakened immune systems or who are at risk for developing serious complications of influenza but may be allergic to the flu vaccine. The first is amantadine hydrochloride, which is marketed under the names Symmetrel (syrup), Symadine (capsule), and Amantadine-hydrochloride (capsule and syrup). The second antiviral is rimantadine hydrochloride, marketed under the trade name Flumandine (tablet and syrup). These two drugs are chemically related and are only effective against type A influenza viruses. Both drugs can cause side effects such as nervousness, anxiety, lightheadedness, and nausea. Side effects are more likely to occur with amantadine. Severe side effects include seizures, delirium, and hallucinations. These are rare and are nearly always limited to people who have kidney problems, seizure disorders, or psychiatric disorders.

Alternative treatment

There are several alternative treatments that may help in fighting off the virus, easing symptoms, and promoting recovery:

  • Acupuncture and acupressure. Both are said to stimulate natural resistance, relieve nasal congestion and headaches, fight fever, and calm coughs, depending on the acupuncture and acupressure points used.
  • Aromatherapy. Aromatherapists recommend gargling daily with one drop each of the essential oils of tea tree (Melaleuca spp.) and lemon mixed in a glass of warm water. If the patient is already suffering from the flu, two drops of tea tree oil in a hot bath may help ease the symptoms. Essential oils of eucalyptus (Eucalyptus globulus) or peppermint (Mentha piperita) added to a steam vaporizer may help clear chest and nasal congestion.
  • Herbal remedies. Herbal remedies such as echinacea can be used to stimulate the immune system; as antivirals, goldenseal (Hydrastis canadensis) and garlic (Allium sativum) can be used. They can also be used to alleviate whatever symptoms arise as a result of the flu. For example, an infusion of boneset (Eupatroium perfoliatum) may counteract aches and fever, and yarrow (Achillea millefolium) or elderflower tinctures may combat chills.
  • Homeopathy. To prevent flu a homeopathic remedy called Oscillococcinum may be taken at the first sign of flu symptoms and repeated for a day or two. Other recommended homeopathic remedies vary according to the specific flu symptoms present. Gelsemium (Gelsemium sempervirens) is recommended to combat weakness accompanied by chills, headache, and nasal congestion. Bryonia (Bryonia alba) may be used to treat muscle aches, headaches, and a dry cough. For restlessness, chills, hoarseness, and achy joints, poison ivy (Rhus toxicodendron) is recommended. Finally, for bodily aches and a dry cough or chills, Eupatorium perfoliatum is suggested.
  • Hydrotherapy. A hot bath to induce a fever will speed recovery from the flu by creating an environment in the body where the flu virus cannot survive. Taking a bath in water as hot as can be tolerated, and remain in the bath for 20-30 minutes, is recommended. While in the bath, drinking a cup of yarrow or elderflower tea helps induce sweating. However, a cold cloth should be held on the forehead or the nape of the neck to keep down the temperature of the brain. In case dizziness or weakness occurs, the patient should be assisted when getting out of the bath. The individual should then go to bed and cover up with layers of blankets to induce more sweating.
  • Vitamins. For adults, 2-3 grams of vitamin C daily may help prevent the flu. Increasing the dose to 5-7 grams per day if infected by the flu can help overcome the infection. The dose of vitamin C should be reduced if diarrhea develops.

Prognosis

Following proper treatment guidelines, healthy people under the age of 65 years of age usually suffer no long-term consequences associated with influenza infections. While the elderly and the chronically ill are at greater risk for secondary infection and other complications, they can also recover completely. While most people fully recover from an influenza infection, the flu should not be viewed with complacency. Influenza is a serious disease. Approximately one in every 1,000 cases proves fatal.

Health care team roles

Family physicians, internists, and pediatricians most often diagnose influenza in people who seek medical attention. Nurse practitioners and physician assistants may also make such diagnoses. A physician usually prescribes over-the-counter products for symptomatic relief. Occasionally, antiviral products are prescribed for people at particular risk. Nurses administer vaccines to prevent influenza, providing education and information to those contemplating or receiving the vaccine.

Prevention

The Centers for Disease Control and Prevention recommend that people—particularly the at-risk population such as children, individuals with other diseases or disorders or a compromised immune system, and the elderly—get an influenza vaccine injection each year before the flu season starts. In the United States the flu season typically runs from late December to early March. Vaccines should be received two to six weeks prior to the beginning of the flu season to allow people's bodies enough time to establish immunity. Adults need only one dose of the yearly vaccine, but children under nine years of age who have not previously been immunized should receive two doses with a month between each dose.

Each season's flu vaccine contains three virus strains that are the most likely to be encountered in the coming flu season. When there is a good match between the anticipated flu strains and the strains used in the vaccine, the vaccine is 70-90% effective in people younger than 65 years of age. Because immune response diminishes somewhat with age, people older than 65 years may not receive the same level of protection from the vaccine as do younger people. Even if they do contract the flu, the elderly benefit from vaccines, which diminish the severity of the illness and help prevent complications.

The virus strains used to make the vaccine are inactivated and will not cause a case of influenza. In the past, flu symptoms following vaccination were associated with vaccine preparations that were not as highly purified as modern vaccines, not to the virus itself. In 1976 there was a slightly increased risk of developing Guillain-Barré syndrome, a very rare disorder associated with the swine flu vaccine. This association occurred only with the 1976 swine flu vaccine preparation and has never recurred.

Serious side effects with modern vaccines are extremely unusual. Some people experience a slight soreness at the point of injection, which resolves within a day or two. People who have never been exposed to influenza, particularly children, may experience one to two days of a slight fever, tiredness, and muscle aches. These symptoms start within six to 12 hours after vaccination.

It should be noted that certain people should not receive an influenza vaccine. Infants six months and younger have immature immune systems and will not benefit from the vaccine. Since the vaccines are prepared using hen eggs, people who have severe allergies to eggs or other vaccine components should not receive the influenza vaccine. As an alternative, they may receive a course of amantadine or rimantadine, which are also used as protective measures against influenza. Other people who might receive these drugs are those who have been immunized after the flu season has started or who are immunocompromised, such as people with advanced HIV disease. Amantadine and rimantadine are 70-90% effective in preventing influenza.

Members of certain groups are strongly advised to be vaccinated because they are at-risk for influenzarelated complications:

  • all people 65 years and older
  • residents of nursing homes and chronic-care facilities, regardless of age
  • adults and children who have chronic heart or lung problems, such as asthma
  • adults and children who have chronic metabolic diseases, such as diabetes and renal dysfunction, as well as severe anemia or inherited hemoglobin disorders
  • children and teenagers receiving long-term aspirin therapy
  • pregnant women who will be in the second or third trimester during flu season, or women who are nursing
  • anyone who is immunocompromised, including HIV-infected people with CD4 count over 200; people with cancer; organ transplant recipients; and people receiving steroids, chemotherapy, or radiation therapy
  • anyone in contact with people in these groups, such as teachers, care givers, health-care personnel, and family members
  • travelers to foreign countries

An individual need not be in one of the at-risk categories listed above, however, to receive a flu vaccination. Anyone who wants to avoid the discomfort and inconvenience of a case of influenza should receive the vaccine.

KEY TERMS

Common cold— A mild illness caused by an upper respiratory virus. Usual symptoms include nasal congestion, coughing, sneezing, throat irritation, and a low-grade fever.

Epidemic— A widespread regional disease outbreak.

Guillain-Barré syndrome— Also called acute idiopathic polyneuritis, this condition is a neurologic syndrome that can cause numbness in the limbs and muscle weakness following certain viral infections.

Pandemic— Worldwide or multiregional outbreak of an infection afflicting millions of people.

Reye's syndrome— A syndrome of nausea, vomiting, and neurological problems such as confusion or delirium. It can be fatal in children.

Resources

BOOKS

Craighead, John E. Pathology and Pathogenesis of Human Viral Disease. New York: Academic Press, 2000.

Dolin, Raphael. "Influenza." In Harrison's Principles of Internal Medicine, 14th ed. Ed. Anthony S. Fauci, et al., New York: McGraw-Hill, 1998, 1096-1098.

Hayden, Frederick G. "Influenza." In Cecil Textbook of Medicine, 21st ed. Ed. Lee Goldman and J. Claude Bennett. Philadelphia: W.B. Saunders, 2000, 1797-1800.

Kolata, Gina B. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It. Carmichael, CA: Touchstone Books, 2001.

Ramen, Fred. Influenza. New York: Rosen Publishing Group, 2001.

Wright, Peter. "Influenza Viruses." In Nelson Textbook of Pediatrics, 16th ed. Ed. Richard E. Behrman et al., Philadelphia: Saunders, 2000, 987-990.

PERIODICALS

Berry, B.B., D.A. Ehlert, R.J. Battiola, and G. Sedmak. "Influenza Vaccination Is Safe and Immunogenic when Administered to Hospitalized Patients." Vaccine 19, nos. 25-26 (2001): 3493-3498.

Chisholm, J.C., T. Devine, A. Charlett, C.R. Pinkerton, and M. Zambon. "Response to Influenza Immunization During Treatment for Cancer." Archives of Diseases of Children 84, no. 6 (2001): 496-500.

Fleming, D.M., and M. Zambon. "Update on Influenza and Other Viral Pneumonias." Current Opinions on Infectious Diseases, 14, no. 2, (2001): 199-204.

Fleming, D.M. "Managing Influenza: Amantadine, Rimantadine and Beyond." International Journal of Clinical Practice 55, no. 3 (2001): 189-195.

Green, M.S. "Compliance with Influenza Vaccination and the Health Belief Model." Israel Medical Association Journal 2, no. 12 (2001): 912-913.

Hak, E., T.J. Verheij, G.A. van Essen, A. B. Lafeber, D.E. Grobbee, and A.W. Hoes. "Prognostic Factors for Influenza-Associated Hospitalization and Death During an Epidemic." Epidemiology of Infections 126, no. 2: 261-268.

James, J.S. "Flu Epidemic: Shots, New Treatments Available." AIDS Treatment News no. 335 (21 Jan. 2000): 2-4.

Michaeli, D. "Influenza Vaccination." Israel Medical Association Journal 2, no. 12 (2000): 914-915.

Wareing, M.D., and G.A. Tannock. "Live Attenuated Vaccines Against Influenza; An Historical Review." Vaccine 19, nos. 25, 26 (2001): 3320-3330.

ORGANIZATIONS

American Academy of Emergency Medicine. 611 East Wells Street, Milwaukee, WI 53202. (800) 884-2236. 〈http://www.aaem.org〉.

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007-1098. (847) 434-4000. 〈http://www.aap.org/default.htm〉.

OTHER

Centers for Disease Control and Prevention. 〈http://www.cdc.gov/ncidod/diseases/flu/fluvirus.htm〉.

Food and Drug Administration. 〈http://www.fda.gov/cder/drug/advisory/influenza.htm〉.

National Coalition for Adult Immunization. 〈http://www.nfid.org/factsheets/influadult.html〉.

National Foundation for Infectious Diseases. 〈http://www.nfid.org/library/influenza〉.

National Institute of Allergy and Infectious Diseases. 〈http://www.niaid.nih.gov/publications/flu.htm〉.

National Library of Medicine. 〈http://www.nlm.nih.gov/medlineplus/influenza.html〉.

World Health Organization. 〈http://www.who.int/emc/diseases/flu/〉.

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Influenza

Influenza

Introduction

Disease History, Characteristics, and Transmission

Treatment and Prevention

Scope and Distribution

Impacts and Issues

Primary Source Connection

BIBLIOGRAPHY

Introduction

Influenza is a viral disease that has plagued humans since the time of learning to walk upright. The medical writings of antiquity contain evidence that implicates influenza in causing epidemics of death and disease. A form of the influenza virus exists in nearly all animals, including domesticated birds and pigs, and these animal viruses bear a close genetic relationship to human influenza viruses.

A typical attack of influenza starts with high fever, chills, muscle aches, a dry cough, and feeling distinctly ill. Soon a sore throat with nasal congestion and a runny nose develops. The cough worsens and misery results. In healthy adults and children, a case of influenza lasts about a week and recovery is complete. Many think the illness is nothing more than a particularly severe “cold.” However, influenza can be unpredictable, and can kill healthy adults and children.

Disease History, Characteristics, and Transmission

Most often, influenza primarily attacks the nose, throat, and lungs, but any part of the body can be infected. Sometimes influenza will cause abdominal pain, nausea, and diarrhea. Rarely, the muscles will be infected and can be severely damaged. Infants may develop a severe form of viral pneumonia with the heart and lungs struggling to sustain life. Influenza can infect the brain as well, resulting in seizures and coma. Influenza is predictably unpredictable in how severe the disease may be in any one person.

Other diseases can take advantage of the weakened state of the body after a case of influenza and cause a secondary infection. Bacteria such as group A streptococcus, Staph aureus, and strep pneumonia are particularly efficient at causing a lethal pneumonia after influenza damages the lungs. About 10% of children will develop a secondary infection while recovering from influenza, and ear infections frequently afflict infants and young children just as they are trying to recover from influenza. The secondary infections often cause another visit to the doctor when parents discover their child, who seemed to be recovering, is ill again.

Influenza is highly contagious and primarily spreads person to person in virus-laden droplets produced by sneezing or coughing. Alternatively, the droplets land on a surface and contaminate the hands that, if not washed, carry the virus to the mouth or nose. Schoolaged children are the main culprits in spreading influenza. Usually 10–40% of school-aged children will get influenza in any one season. They swap virus at school and bring it home to infect family members. Children are contagious before they even appear or feel ill, and the virus is present in nasal mucous and cough droplets for over a week after apparent recovery from influenza.

The microbiology of the influenza virus is quite complex. Influenza viruses consist of three different major types known as A, B, and C. Of the three types, only A and B cause significant disease in humans. Both A and B types cause the seasonal epidemics around the world, but at any one time there may be hundreds of different variations of each type circulating the globe. This multitude of subtly different varieties presents a challenge to the human immune system.

Both influenza A and B virus change their structure often enough such that the immune system can never develop long-lasting immunity. Influenza B virus changes much more slowly than influenza A and usually causes milder illness compared to influenza A. However, influenza B can cause severe disease in the elderly, those with impaired immunity, or those with chronic lung or heart disease.

Influenza A generally causes more severe disease and is the most unpredictable. The yearly season epidemics of the “flu” are primarily the result of influenza A. The virus has two specific proteins on its surface, which are important for infecting humans. These proteins, known as antigens, bear the names hemagglutinin (HA) and neuraminidase (NA). The HA and NA proteins vary in their chemical structure from year to year. This process, termed antigenic drift, results in virus particle proteins with subtle variations in structure. Fifteen different HA subtypes are known to exist while there are nine NA subtypes. These slightly different proteins get different number designations, and the various influenza strains are named by the specific HA and NA proteins on the virus. The H3N1 virus contains HA protein 3 and NA protein 1.

Influenza A employs an additional means of evading the immune system. When two different viral strains infect someone at the same time, the two viral variants will swap component genes and create yet another slightly different form of influenza. The new virus will contain some proteins of one variety of influenza A and some proteins of the other variety. This sloppy way of making new virus particles extends to swapping genetic material with animal or bird influenza viruses. This process, termed antigenic shift, will sometimes create an influenza virus for which humans have no immunity at all. A novel virus produced this way has the potential to spread worldwide, resulting in a pandemic.

Three influenza pandemics have occurred in the twentieth century. The influenza pandemic in 1918 killed at least twenty million people, and some experts think there were fifty million deaths within a period of 24 weeks. Nearly as many United States soldiers died of influenza in 1918 as died in battle in all of World War I. In the United States, the 1957 pandemic resulted in 70,000 deaths while in 1968 about 30,000 died. During influenza pandemics, a larger proportion of healthy adults die than during the yearly “flu season” outbreaks.

WORDS TO KNOW

ANTIGEN: Antigens, which are usually proteins or polysaccharides, stimulate the immune system to produce antibodies. The antibodies inactivate the antigen and help to remove it from the body. While antigens can be the source of infections from pathogenic bacteria and viruses, organic molecules detrimental to the body from internal or environmental sources also act as antigens. Genetic engineering and the use of various mutational mechanisms allow the construction of a vast array of anti-bodies (each with a unique genetic sequence).

ANTIGENIC SHIFT: Antigenic shift describes an abrupt and major genetic change (e.g. in genes coding for surface proteins of a virus).

DROPLET TRANSMISSION: Droplet transmission is the spread of microorganisms from one space to another (including from person to person) via droplets that are larger than 5 microns in diameter. Droplets are typically expelled into the air by coughing and sneezing.

PANDEMIC: Pandemic, which means all the people, describes an epidemic that occurs in more than one country or population simultaneously.

STRAIN: A subclass or a specific genetic variation of an organism.

Treatment and Prevention

Medicine has developed weapons with which to combat influenza, specifically the adamantanes and the neuraminidase inhibitor drugs. The adamantanes treat only influenza A while the neuraminidase inhibitors will treat both influenza A and B. Both of these classes of medicines interfere with the ability of the influenza virus to make more virus particles. They either stop production of the viral genetic material or prevent the viral particles from escaping from infected cells to infect other cells. In order to help relieve symptoms or shorten the course of influenza, one must take these drugs early in the course of influenza. Once the illness is established and new influenza virus particles have replicated, the medications are largely ineffective. Many of the symptoms of influenza are due to the damage the virus does to the body during the making of new virus particles so stopping the virus early provides the greatest relief in symptoms.

Until effective medications became available to treat influenza, determining who has influenza rather than one of a similar multitude of viral respiratory illnesses was of little use. Treatment involved decreasing the fever, resting, and drinking plenty of fluids. This treatment is appropriate for most viral illnesses, but now with medications available, there is a difference whether the illness is a “cold” or the “flu” and testing for influenza is often done.

Several rapid tests are available to detect the influenza virus. These tests, often run in a doctor's office, use a sample of mucus taken from the nose or from the back of the throat. The tests are rapid usually taking only five minutes and will detect influenza virus accurately about 75-85% of the time if properly done.

Contrary to popular belief, antibiotics are not effective treatment for influenza. Antibiotics are useful in the treatment of bacterial infections and have no benefit during viral illnesses. Antibiotics may be helpful if secondary bacterial infections develop during the course of influenza.

Drugs provide a treatment option unavailable in past decades, but they do not provide the best option for control of influenza. Many will not realize their illness is influenza until it is too late for medications to be effective. Additionally they have usually already spread influenza to family members and co-workers.

Influenza vaccination provides the most effective treatment by preventing the disease, but the influenza virus poses a challenge for vaccine development. Since the virus changess lightly year to year and changes dramatically at unpredictable intervals, vaccines also need altering from year to year. Each year, public health officials make an educated guess as to what will be the prevalent strains circulating in the next season, and vaccine preparation commences targeting those strains.

Influenza vaccines provide excellent protection when administered at least two weeks before exposure to the influenza virus, and vaccination is needed each year. The vaccine itself does not cause influenza, but depending on the exact form of vaccine administered, side effects may include soreness at the injection site, muscle aches, runny nose, or sore throat. Young children often need two doses of vaccine for full protection. In the United States, the current vaccine recommendations include everyone older than 65 years, those between six months and five years, and everyone with chronic health problems involving the lungs or heart.

Scope and Distribution

Every year about 35,000 deaths occur in the United States due to influenza. Most of these deaths are those older than 65 years, but more children die of influenza or its complications each year than all the deaths due to whooping cough and measles combined. The World Health Organization credits influenza with causing between 250,000 and 500,000 deaths yearly throughout the world. For example, in 2002, an influenza outbreak started in Madagascar. Over a period of three months, 27,000 people developed influenza, and despite rapid medical intervention, 800 deaths occurred.

Impacts and Issues

Unless a family member or close friend dies of influenza, many people do not really give much thought to the impact influenza has on their health and pocketbook. Influenza ranks far behind heart disease and cancer as a worldwide cause of death, yet its economic impact is considerable. Public health experts have estimated a cost of $60-$4,000 for every case of influenza in a healthy adult in the United States. These costs include direct medical expenses, lost wages, and lost productivity at work. For parents, the cost often includes lost work while caring for the sick child, and afterwards, lost work from the case of influenza caught from the child.

A pandemic raises great concern for public health officials worldwide. Influenza pandemics occur several times a century but are unpredictable as to the exact timing. Each of the past three influenza pandemics (in 1918, 1957, and 1968) resulted from human influenza virus sharing genetic material with a bird influenza virus. Human immune systems had never encountered the new virus, and everyone was susceptible to the new form of influenza. As a result, the new virus swept through countries throughout the globe.

The pandemic of 1918 deserves further explanation as medical history warns that a similar event at some point in the future is highly likely. In the 1918 pandemic, about one third of the world's population suffered a severe case of influenza, and nearly 3% of those infected with the virus died. An unusually high percentage of the young and healthy died during this pandemic. All current strains of influenza A virus are descended from the 1918 virus, but the current strains have weakened considerably. Now less than 0.1% of people die when infected by today's forms of influenza.

Given that the medical system has advanced since 1918, what would be the impact of a new, more lethal influenza virus today? The answer is that the impact could be devastating. Public health experts predict an estimated 90,000–200,000 deaths, over 700,000 hospital admissions, and about forty million visits to doctors in the United States alone. The estimated economic impact exceeds $160 billion, not including the disruptions due to illness in the police, transportation workers, and the health workers themselves.

Over the past several years, a particularly vicious strain (type) of avian (bird) flu, known as H5N1 influenza, has caused many cases of disease and death in humans. Presently, transmission of this virus from human to human does not readily occur. Close contact with infected birds is required to catch this form of influenza. If this bird virus ever acquires the ability to infect humans from one person to another, a new pandemic could occur. The Center for Disease Control and the World Health organization recognize this possibility, and planning for the potential pandemic continues.

Primary Source Connection

Scientists at the Centers for Disease Control and Prevention play a key role in accessing influenza viruses and formulating vaccines for them. In order to prepare for a future pandemic influenza, CDC scientists studied the characteristics of the 1918 pandemic flu virus. The CDC press release below, released in February 2007, relates that by manipulating the 1918 virus, CDC scientists have found a way to render it less capable of spreading among animals that were in close contact with each other. This type of research could prove beneficial in reducing the ability of future influenza viruses to spread rapidly across heavily populated regions and cause a pandemic.

Small Changes in 1918 Pandemic Virus Knocks Out Transmission: Research Provides Clues for Assessing Pandemic Potential of New Influenza Viruses

Press Release

Embargoed Until 2 p.m. EST: February 1, 2007

Contact:

CDC Media Relations

(404) 639-3286

Experts at the Centers for Disease Control and Prevention have shown that a molecular change in the 1918 pandemic influenza virus stops its transmission in ferrets that were in close proximity, shedding light on the properties that allowed the 1918 pandemic virus to spread so quickly and potentially providing important clues that could help scientists assess emerging influenza viruses, such as H5N1.

The study, which is published in the Feb. 5 issue of Science, showed that a modest change of two amino acids in the main protein found on the surface of the 1918 virus did not change the virus's ability to cause disease, but stopped respiratory droplet transmission of the virus between ferrets placed in close proximity. The experiments were conducted with ferrets because their reaction to influenza viruses closely mimics how the disease affects humans.

“With this vital research, we are learning more about what may have contributed to the spread and deadliness of the 1918 pandemic,” said CDC Director Dr. Julie Gerberding. “By better understanding how this virus spreads, we can be better positioned to slow down or stop the spread of the pandemic virus and hence be better prepared for the next pandemic.”

To spread and cause illness, the influenza virus must first bind to host cells found in humans and animals. The Science study suggests that the hemagglutinin (HA), a type of protein found on the surface of influenza viruses, plays an important role in the 1918 virus's ability to transmit from one host to another efficiently. This research suggests that, for an influenza virus to spread efficiently, the virus's HA must prefer attaching to cells that are found predominately in the human upper airway instead of cells found predominately in the gastrointestinal tracts of birds. Other changes may be necessary as well. Current H5N1 viruses prefer attaching to avian cells, suggesting the virus would need to make genetic changes before it could pass easily between humans.

“Work on the 1918 virus is providing clues that are helping us evaluate other influenza viruses with pandemic potential, such as H5N1, that may emerge,” said Dr. Terrence Tumpey, lead author of the paper and a CDC senior microbiologist. “Though we still don't know what changes might be necessary for H5N1 to transmit easily among people, it's likely that changes in more than one virus protein would be required for the H5N1 virus to be transmitted among humans.”

Influenza pandemics occur when a new strain emerges to which people have little or no immunity. Most experts argue another pandemic will occur, but it is impossible to predict which strain will emerge as the next pandemic strain, when it will occur or how severe it will be.

The 1918 pandemic caused an estimated 675,000 deaths in the United States and up to 50 million worldwide, in the worst pandemic of the past century.

The research was done in collaboration with Mount Sinai School of Medicine and the Southeast Poultry Research Laboratory. All laboratory work with 1918 virus was conducted at CDC in a high containment Biosafety Level 3 laboratory with enhancements, using stringent biosecurity precautions to protect both laboratory workers and the public from exposure to the virus. Currently available antiviral drugs have been shown to be effective against the 1918 influenza virus and similar viruses.

Centers for Disease Control and Prevention (CDC)

CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC). “SMALL CHANGES IN 1918 PANDEMIC VIRUS KNOCKS OUT TRANSMISSION.” PRESS RELEASE. FEBRUARY 1, 2007. <HTTP://WWW.CDC.GOV/OD/OC/MEDIA/PRESSREL/2007/R070201.HTM> (ACCESSED JUNE 4, 2007).

See AlsoDroplet Precautions; H5N1 Virus; Influenza Pandemic of 1918; Influenza Pandemic of 1957; Influenza, Tracking Seasonal Influences and Virus Mutation; Pandemic Preparedness; Vaccines and Vaccine Development; Viral Disease.

BIBLIOGRAPHY

Books

Barry, John M. The Great Influenza: The Story of the Deadliest Pandemic in History. New York: Penguin Books, 2004.

Goldsmith, Connie. Influenza: The Next Pandemic? Brookfield, CT: Twenty-first Century Books, 2006.

Web Sites

Centers for Disease Control and Prevention. “Influenza (Flu).” <http://www.cdc.gov/flu> (accessed June 4, 2007).

World Health Organization. “Influenza.” <http://www.who.int/topics/influenza/en> (accessed June 4, 2007).

Lloyd Scott Clements

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Influenza

Influenza

Definition

Influenza, also referred to as the flu, is a highly contagious disease of the nose, throat, and lungs that is caused by an influenza virus.

Description

There are three types of influenza viruses , A, B, and C. Influenza Types A and B viruses cause seasonal epidemics of disease most winters in the United States. Influenza Type C viruses cause only mild respiratory illnesses, are not thought to be responsible for epidemics, and are not included in influenza vaccines. There are two types of subtypes of Influenza A viruses found in human beings: H1N1 and H3N2. Influenza B viruses do not exhibit subtypes. Type A viruses tend to affect adults while Type B viruses affect children. Each year strains of Influenza A subtype H1N1 and H3N2 and a strain of Influenza B are included in the influenza vaccine. The strain of viruses included in the vaccine change yearly based on international surveillance data of influenza cases and estimations by scientists on what types and strains of viruses will be prevalent in the coming year. When the strains included in the vaccine are well-matched to the strains in the community, the vaccine usually can protect seven to nine out of ten vaccinated persons. However, in elderly people, the vaccine may not work as well to prevent contracting of influenza, but will result in decrease in the severity of symptoms and the risk of health complications.

The illness known as stomach flu is not a form of influenza. The influenza virus normally does not attack the stomach or intestines. Stomach flu is caused by other organisms, such as salmonella or Escherichia coli bacteria.

Influenza season can run from as early as October and can last as long as May. Winter is usually the prime season for influenza, as flu activity has peaked in January during 26 of the last 30 influenza seasons. During a single influenza season, there may be more than one outbreak of activity due to infections by different strains of the influenza viruses, and an individual may get influenza more than once.

Periodically an influenza strain arises that is very different from other strains. When this major change occurs, a world wide epidemic, called a pandemic, can develop. Few people will have antibodies against the new virus. In 1918-1919, such a pandemic occurred due to an influenza outbreak referred to as the Spanish flu, and it is estimated that 40 to 100 million people died. In 1957-58 the Asian flu pandemic killed 1 to 1.5 million people, and the Hong Kong flu pandemic in 1968-1969 killed 0.75 to 1 million people.

Demographics

About 10 to 20 percent of the United States population contracts influenza each year. An average of 36,000 people die from influenza-related complications and more than 200,000 are hospitalized. More than half of those hospitalized are people aged 65 years or older, as senior citizens are generally more at risk for serious influenza complications.

Causes and symptoms

In healthy adults, influenza is typically a moderately severe illness. However in adults over the age of 65 and for people with health problems, influenza may be a dangerous disease. Influenza usually starts abruptly, with a high fever of 102 to 106 degrees Fahrenheit. The fever lasts for a day or two, but may last up to 5 days. Other symptoms include flushed face, body aches and chills, nausea, loss of appetite, weakness, and lack of energy. Some people may have dizziness or vomiting. After two to four days, respiratory symptoms, such as a dry, hacking cough, nasal discharge, and sneezing, appear and last for four to seven days. The patient may also suffer from sore throat and headache and the fever could return. Coughing and fatigue can last for weeks after the acute symptoms subside. It is recommended that a person stay at home as long as the illness is severe, and for about two days after the fever subsides. Generally the symptoms of influenza are more severe than those of the common cold . Cold symptoms rarely include fever, headache, aches and pains, and extreme exhaustion.

The most common way to become infected with an influenza virus is by breathing in droplets from the coughs or sneezes of an infected person. The disease can also be contracted by persons touching a contaminated surface and then touching their mouth, nose, or eyes. After a person is infected with an influenza virus, symptoms usually appear within 2 to 4 days, and the person is contagious for another 3 to 4 days after the symptoms appear.

Adults over the age of 65 who contract influenza are more likely to develop serious complications, thus affecting their health and their independence . Diseases that place persons at high risk include:

  • chronic lung diseases such as asthma, emphysema, chronic bronchitis, tuberculosis, or cystic fibrosis
  • heart disease
  • chronic kidney disease
  • diabetes or other chronic metabolic disorders
  • severe anemia
  • diseases or treatments that depress the immune system

QUESTIONS TO ASK YOUR DOCTOR

  • What can I do to relieve my symptoms?
  • Do I need further testing to see if I have developed influenza-related complications?

Possible complications that may develop, especially for those at high risk, include pneumonia , encephalitis, bronchitis , sinus infections, ear infections, or exacerbation of existing chronic diseases such as congestive heart failure , asthma , or diabetes. Most people who die from influenza-related complications are 65 years or older.

Diagnosis

To diagnosis if a person has influenza, a thorough physical examination should be conducted. When influenza is widespread in a community, such an examination of symptoms may be sufficient for diagnosis. However, based on symptoms alone, it may be difficult to distinguish influenza from such diseases caused by infectious agents such as Mycoplasma pneumoniae, adenovirus, respiratory syncytial virus, rhinovirus, parainfluenza viruses, and Legionella species. An antigen detection test of a sample collected from the nasal passages (nasal swab) should conducted to provide a definite diagnosis if results are needed to determine appropriate treatment decisions. A chest x-ray should be performed if pneumonia is suspected, as pneumonia is a common complication of influenza. If there is an outbreak of illness in a hospital or a nursing home, testing for influenza may be required to determine the cause of the outbreak. Collection and analysis of selected samples will also provide information on what strains are causing illnesses, compared to the strains included in the annual vaccine, as well as provide information on new strains to be considered for the next year's vaccine.

Treatment

Rest, the use of symptom-relieving medications, and ingestion of liquids are sufficient treatments for persons with low risk of complications and mild symptoms. The use of aspirin , alcohol, and tobacco should be avoided, and antibiotics are not necessary, unless bacterial complications arise. If symptoms do not improve after several days, or if symptoms get progressively worse, a person should visit a physician to be checked for possible complications.

If the flu is diagnosed within 48 hours of when symptoms begin, antiviral medications may be taken to help shorten the duration of the illness and reduce the severity of the symptoms. The medications are not effective if taken more than 48 hours after onset of the disease. The use of antiviral medication may also prevent the development of influenza-related complications.

Two antiviral medications that are available are oseltamivir and zanamivir. The recommended duration of treatment with these medications is five days. Potential side effects of oseltamivir are vomiting or nausea, while rare cases of self-injury or delirium have been reported. Zanamivir should not be used by persons with respiratory diseases such as asthma or chronic obstructive pulmonary disease . Oseltamivir can be taken in capsule or oral suspension form, while zanamivir is self-administered by oral inhalation.

Two other licensed influenza antiviral agents are available in the United States: amantadine and rimantadine. Since Influenza A virus resistance to amantadine and rimantadine can emerge rapidly during use, the Advisory Committee on Immunization Practices of the Center for Disease Control recommended that neither amantadine nor rimantadine be used for the treatment or prevention of influenza A in the United States during the 2007-08 influenza season.

Nutrition/Dietetic concerns

By maintaining a healthy diet , a person is more likely to have a stronger immune system , which in turn reduces the risk of getting influenza and perhaps lessening the duration and severity of symptoms if influenza is contracted.

Prognosis

Tens of millions of people in the United States get influenza each year. Most people who get influenza recover within a week or two but thousands do become hospitalized. About 36,000 people die yearly in the United States because of influenza-related complications.

Prevention

The best way to prevent contracting influenza is to get an annual influenza vaccination . The vaccination, which is safe and effective, takes about two weeks to provide protection against influenza. In the United States the Medicare program covers the cost of the vaccine.

KEY TERMS

Epidemic —The occurrence of more cases of a disease than would be expected in a community or region during a given time period; a sudden severe outbreak of a disease.

Pandemic —An epidemic (a sudden outbreak) that becomes very widespread and affects a whole region, a continent, or the world.

Vaccination —Injection of a killed or weakened microbe in order to stimulate the immune system against the microbe, thereby preventing disease. Vaccinations, or immunizations, work by stimulating the immune system, the natural disease-fighting system of the body. The healthy immune system is able to recognize invading bacteria and viruses and produce substances (antibodies) to destroy or disable them. Vaccinations prepare the immune system to ward off a disease. To immunize against viral diseases, the virus used in the vaccine has been weakened or killed.

Virus —A microorganism smaller than a bacteria, which cannot grow or reproduce apart from a living cell. A virus invades living cells and uses their chemical machinery to keep itself alive and to replicate itself. It may reproduce with fidelity or with errors (mutations)-this ability to mutate is responsible for the ability of some viruses to change slightly in each infected person, making treatment more difficult.

Antiviral drugs oseltamivir and zanamivir, which can be taken by persons who have not yet contracted influenza, are 70 to 90 percent effective in preventing influenza and are useful to use in conjunction with vaccination. An antiviral drug must be taken every day during potential exposure to influenza or for 14 days after receiving an influenza vaccination, to allow time for immunity to develop.

As influenza is easily passed through sneezing, coughing, and contact with contaminated surfaces, staying away from people with the flu and frequent hand washing with soap and water or with an alcohol-based hand cleaner are also methods of preventing influenza infections.

Caregiver concerns

Caregivers of the elderly should receive influenza vaccinations annually to protect the people in the care from getting the disease. Vaccination of health care professionals has been associated with fewer deaths among nursing home patients and elderly hospitalized patients. However, only 42 percent of health care professionals become vaccinated in the United States each year. During influenza outbreaks, even caregivers who have been vaccinated should consider taking antiviral drugs, especially when caring for seniors at high risk for complications.

Resources

BOOKS

Monto, Arnold S. Contemporary Diagnosis, Prevention, and Management of Influenza. Newtown, PA: Handbooks in Health Care Company, 2002

Schachter, Neil. The Good Doctor's Guide to Colds and Flu.

New York, NY: HarperCollins Publishers, 2005.

Williams, J.E. Beating the Flu: The Natural Prescription for Surviving Pandemic Influenza and Bird Flu. Charlottesville, VA: Hampton Roads Publishing Company, 2006.

ORGANIZATIONS

Centers for Disease Control and Prevention Influenza, www.cdc.gov/flu/.

National Institute of Allergy and Infectious Diseases, National Institutes of Health, http://www3.niaid.nih.gov/healthscience/healthtopics/Flu/default.htm.

Judith L. Sims

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Influenza

INFLUENZA


Influenza (flu) is an important cause of morbidity and mortality. Flu is caused by infection with the influenza virus, a member of the Orthomyxoviridae family. Infection leads to illness, typically lasting a week, characterized by fever, sore throat, cough, headache, runny nose, and fatigue. Mild cases of flu can result in the common cold. In the medically more severe cases of flu, and in all fatal cases, a secondary pneumonia arises as a complication.

Flu is spread from person to person through sneezing and coughing. Influenza is zoonotic, that is, it has an animal origin, with avian and porcine strains able to jump species. The flu genome consists of eight single strands of RNA, which means that new strains can arise whenever an individual is infected with two existing strains. To be effective, flu vaccines, formulated on the basis of surveillance of early cases, must be given every year because of these constantly-changing strains.

Influenza is an epidemic disease in several respects. There is great year-to-year variability in morbidity, mortality, and incidence, and more intense periods are labeled as epidemics. New strains spread in epidemic style across regions, documented in a rich body of work by medical geographers, using both historical and modern data. There are occasional pandemics–severe outbreaks, global in scope; twentieth century pandemics occurred in 1918, 1946–1947, 1957, and 1968.

Age Profiles of Mortality

Figure 1 shows the age profile of death rates (per 100,000 population) for influenza and pneumonia (combined) for males and females in the United States in the years 1900, 1918, 1939, and 1998. Since fatal cases of influenza involve pneumonia, it is customary for statistical bureaus to merge influenza and pneumonia in published vital statistics. The patterns in the figure illustrate notable aspects of influenza demography and yield insight into mortality patterns more generally. To permit comparisons, all four panels in the figure are drawn to the same scale, with a horizontal rule across each panel at a mortality level of 100 per 100,000.

The influenza mortality rates exemplify three major mortality age patterns, named after letters of the alphabet: U, W, and J. In 1900, the pattern is U-shaped (sometimes called V-shaped), with peak

FIGURE 1

mortality at the upper and lower ranges of the age distribution. Though influenza occurs at all ages, mortality is concentrated among the youngest and oldest. A similar pattern is seen in 1939, except that the base of the U (but not the top prongs) has descended to a lower level and remains below the 100 per 100,000 line until a much later age. The 1939 panel represents the end of the pre-antibiotic era. Flu, being a viral disease, is not treatable with antibiotics, but secondary pneumonias often involve or are exacerbated by bacterial coinfection, which can be treated with antibiotics.

The mortality pattern in 1918 is completely atypical, even for a pandemic. Due to that year's epidemic of hypervirulent influenza, the pattern is W-shaped, with a peak at middle age in addition to peaks at infancy and old age. Such a pattern is unusual among biological causes of death: tuberculosis is perhaps the closest parallel. The entire mortality curve in 1918 lies above the 100 per 100,000 line, reflecting the severity of the epidemic. The male excess death rate, in absolute terms, was also exceptionally high in 1918, particularly at the middle-age peak of the W-pattern. The leading explanation for the decline in death rates above age 35, which gives rise to the W shape, is that at least one flu strain that was circulating in the late nineteenth century was similar to the 1918 strain, and had imparted partial immunity to those who, by 1918, were above age 35; in demographic terms, it is a cohort-effect explanation.

Since 1950, influenza death rates in developed countries have declined more at young ages than among the elderly, transforming the U shape into a J shape, as seen in the 1998 data.

The 1918 Epidemic

The 1918 influenza epidemic was an important event not only in the history of influenza, but also in world demographic history. Usual estimates are 20 to 40 million deaths worldwide, with great uncertainty because much of the world did not have vital registration in 1918. By the measure of its death toll and its global reach, it was the biggest epidemic of any disease in the twentieth century. In the United States, the estimate is 550,000 deaths (0.5% of the population), with about one-fourth of the population having had recognizable cases of flu. The 1918 epidemic is sometimes called the "Spanish flu." It is not thought to have had a Spanish origin, but since Spain, as a neutral power, did not censor newspapers during World War I, early accounts of the flu came from Spain. There is debate about whether the epidemic began in the United States and then spread to Europe and the rest of the world, or vice versa. Late twentieth and early twenty-first century studies, using modern laboratory techniques and preserved tissue samples, have focused on deciphering the molecular basis for the virulence of the 1918 strain, so far without conclusive results.

There is a hypothesis, based on data from the United States, that the 1918 influenza epidemic had a selective effect. Specifically, the suggestion is that many of those who died of flu in 1918 already had chronic illness (most notably, tuberculosis, highly prevalent at the time). The supporting evidence is that after 1918, death rates, especially from tuberculosis, dropped relative to their pre-1918 trend. The logic is that if the 1918 victims had already been sicker than average, then the post-1918 population would be healthier and therefore death rates should decline. It is rare to see such selection effects in the population at large, but the magnitude of the 1918 epidemic was large enough to be exploited as a natural experiment (i.e., a natural event which mimics an actual experiment in certain respects).

As noted, there has been little reduction in influenza and pneumonia death rates above age 80, in contrast to younger ages, which have seen dramatic declines. With the worldwide population aging, influenza is certain to remain an important cause of death for many years to come. Moreover, the possibility of another pandemic of hypervirulent influenza, comparable to that of 1918, cannot be ruled out.

See also: Diseases, Infectious; Epidemics.

bibliography

Crosby, Alfred W. 1989. America's Forgotten Pandemic: The Influenza of 1918. Cambridge, Eng.: Cambridge University Press.

Kilbourne, Edwin D. 1987. Influenza. New York: Plenum.

Kolata, Gina. 1999. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It. New York: Farrar, Strausand Giroux.

Noymer, Andrew, and Michel Garenne. 2000. "The 1918 Influenza Epidemic's Effects on Sex Differentials in Mortality in the United States." Population and Development Review 26(3): 565–581.

Pyle, Gerald F. 1986. The Diffusion of Influenza: Patterns and Paradigms. Totowa, NJ: Rowman & Littlefield.

Andrew Noymer

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Influenza

Influenza

Definition

Usually referred to as the flu or grippe, influenza is a highly infectious respiratory disease caused by certain strains of influenza virus. When the virus is inhaled it attacks cells in the upper respiratory tract causing typical flu symptoms such as fatigue, fever and chills, hacking cough, and body aches. Influenza victims are also susceptible to potentially life-threatening secondary infections. Although the stomach or intestinal upsets and diarrhea are commonly called "flu," the influenza virus rarely causes gastrointestinal symptoms. Such symptoms are most likely due to other organisms such as rotavirus, Salmonella, Shigella, or Escherichia coli.

Description

Influenza is considerably more debilitating than the common cold . Influenza outbreaks occur suddenly and infection rapidly spreads. The annual death toll attributable to influenza and its complications averages 20,000 in the United States alone.

Influenza outbreaks occur on a regular basis. Pandemics, the most serious outbreaks, affect millions of people worldwide and last for several months. The 1918–1919 influenza outbreak serves as the primary example of an influenza pandemic. In that Spanish flu pandemic, the death toll reached a staggering 20–40 million people worldwide. Approximately 500,000 of these fatalities occurred in the United States. Pandemics also occurred in 1957 and 1968 with the Asian flu and Hong Kong flu, respectively. The Asian flu was responsible for 70,000 deaths in the United States, while the Hong Kong flu killed 34,000 people.

Epidemics are widespread regional outbreaks that occur every two to three years and affect 5–10% of the population. The Russian flu in the winter of 1977 is an example of an epidemic. A regional epidemic is shorter lived than a pandemic, lasting only several weeks. Finally, there are smaller outbreaks each winter that are confined to specific locales.

The earliest existing descriptions of influenza were written nearly 2,500 years ago by the ancient Greek physician, Hippocrates. Historically, influenza was ascribed to a number of different agents, including "bad air" and several different bacteria . It was not until 1933 that the causative agent was identified as a virus.

There are three types of influenza viruses , identified as A, B, and C. Influenza A can infect a range of species, including humans, pigs, horses, and birds, but only humans are infected by types B and C. Influenza A is responsible for most flu cases, while infection with types B and C viruses are less common and cause a milder illness.

Causes and symptoms

Approximately one to four days after infection with the influenza virus, a person is hit with an array of symptoms. "Hit" is an appropriate term, because symptoms are sudden, harsh, and followed by overall bodily aches and a fever that may run as high as 104°F (40°C). As the fever subsides, nasal congestion and a sore throat become noticeable. Persons with the flu feel extremely tired and generally miserable. Typical influenza symptoms include the abrupt onset of a headache, dry cough, and chills, and a rapid onset of physical weakness. Normal energy levels typically do not return for several days, but this can extend up to two weeks.

Influenza complications usually arise from secondary bacterial infections of the lower respiratory tract. Signs of a secondary respiratory infection often appear just as a person seems to be recovering. These signs include high fever, intense chills, chest pains associated with breathing, and a productive cough with thick, yellowish-green sputum. If these symptoms appear, medical treatment is necessary. Other secondary infections, such as sinus or ear infections, may also require medical intervention. Heart and lung problems and other chronic diseases can be aggravated by influenza. This is a particular concern among elderly people.

With children and teenagers, it is advisable to be alert for symptoms of Reye's syndrome, a rare but serious complication of the flu. Symptoms of Reye's syndrome are nausea and vomiting, and—more seriously— neurological problems such as confusion or delirium. Among children Reye's syndrome can be fatal. The syndrome has been associated with the use of aspirin to relieve flu symptoms.

Diagnosis

Although specific laboratory tests can be performed on respiratory samples to identify a flu virus strain, doctors typically rely on a set of symptoms and the presence of influenza in the community for diagnosis. Specific tests are useful to determine the type of flu in the community, but they do little to influence individual treatment. Doctors may administer tests, such as throat cultures, to identify and treat secondary bacterial infections.

Treatment

Essentially, little can be done for a case of influenza an it must simply run its course. Symptoms can be relieved with bed rest and by keeping well hydrated. A steam vaporizer may make breathing easier, and pain relievers such as ibuprofen and acetaminophen will relieve most aches and pains. Food may not seem appetizing, but an effort should be made to consume nourishing food. Returning to normal activities too quickly invites a possible relapse or complications.

Drugs

Since influenza is a viral infection, antibiotics are not an effective treatment. However, antibiotics are frequently used to treat secondary infections. Over-thecounter medications are used to treat symptoms, but it is not necessary to purchase a product marketed specifically for flu symptoms. Any medication designed to relieve pain and coughing will provide some relief. Products containing alcohol, however, should be avoided because of the dehydrating effects of alcohol. The best medicine for symptoms is simply an analgesic, such as acetaminophen or ibuprofen. Without a doctor's approval, aspirin is generally not recommended for people under the age of 18 years owing to its association with Reye's syndrome. As a precaution against the syndrome, children should receive acetaminophen or ibuprofen to treat their symptoms.

There are two antiviral drugs marketed for use in the United States against the influenza virus. These may be useful in treating individuals who have weakened immune systems or who are at risk for developing serious complications of influenza but may be allergic to the flu vaccine. The first is amantadine hydrochloride, which is marketed under the names Symmetrel (syrup), Symadine (capsule), and Amantadine-hydrochloride (capsule and syrup). The second antiviral is rimantadine hydrochloride, marketed under the trade name Flumandine (tablet and syrup). These two drugs are chemically related and are only effective against type A influenza viruses. Both drugs can cause side effects such as nervousness, anxiety , lightheadedness, and nausea. Side effects are more likely to occur with amantadine. Severe side effects include seizures, delirium, and hallucinations. These are rare and are nearly always limited to people who have kidney problems, seizure disorders, or psychiatric disorders.

Alternative treatment

There are several alternative treatments that may help in fighting off the virus, easing symptoms, and promoting recovery:

  • • Acupuncture and acupressure . Both are said to stimulate natural resistance, relieve nasal congestion and headaches, fight fever, and calm coughs, depending on the acupuncture and acupressure points used.
  • • Aromatherapy. Aromatherapists recommend gargling daily with one drop each of the essential oils of tea tree (Melaleuca spp.) and lemon mixed in a glass of warm water. If the patient is already suffering from the flu, two drops of tea tree oil in a hot bath may help ease the symptoms. Essential oils of eucalyptus (Eucalyptus globulus) or peppermint (Mentha piperita) added to a steam vaporizer may help clear chest and nasal congestion.
  • • Herbal remedies. Herbal remedies such as echinacea can be used to stimulate the immune system ; as antivirals, goldenseal (Hydrastis canadensis) and garlic (Allium sativum) can be used. They can also be used to alleviate whatever symptoms arise as a result of the flu. For example, an infusion of boneset (Eupatroium perfoliatum) may counteract aches and fever, and yarrow (Achillea millefolium) or elderflower tinctures may combat chills.
  • • Homeopathy. To prevent flu a homeopathic remedy called Oscillococcinum may be taken at the first sign of flu symptoms and repeated for a day or two. Other recommended homeopathic remedies vary according to the specific flu symptoms present. Gelsemium (Gelsemium sempervirens) is recommended to combat weakness accompanied by chills, headache, and nasal congestion. Bryonia (Bryonia alba) may be used to treat muscle aches, headaches, and a dry cough. For restlessness, chills, hoarseness, and achy joints, poison ivy (Rhus toxicodendron) is recommended. Finally, for bodily aches and a dry cough or chills, Eupatorium perfoliatum is suggested.
  • • Hydrotherapy. A hot bath to induce a fever will speed recovery from the flu by creating an environment in the body where the flu virus cannot survive. Taking a bath in water as hot as can be tolerated, and remain in the bath for 20–30 minutes, is recommended. While in the bath, drinking a cup of yarrow or elderflower tea helps induce sweating. However, a cold cloth should be held on the forehead or the nape of the neck to keep down the temperature of the brain . In case dizziness or weakness occurs, the patient should be assisted when getting out of the bath. The individual should then go to bed and cover up with layers of blankets to induce more sweating.
  • • Vitamins. For adults, 2–3 grams of vitamin C daily may help prevent the flu. Increasing the dose to 5–7 grams per day if infected by the flu can help overcome the infection. The dose of vitamin C should be reduced if diarrhea develops.

Prognosis

Following proper treatment guidelines, healthy people under the age of 65 years of age usually suffer no long-term consequences associated with influenza infections. While the elderly and the chronically ill are at greater risk for secondary infection and other complications, they can also recover completely. While most people fully recover from an influenza infection, the flu should not be viewed with complacency. Influenza is a serious disease. Approximately one in every 1,000 cases proves fatal.

Health care team roles

Family physicians, internists, and pediatricians most often diagnose influenza in people who seek medical attention. Nurse practitioners and physician assistants may also make such diagnoses. A physician usually prescribes over-the-counter products for symptomatic relief. Occasionally, antiviral products are prescribed for people at particular risk. Nurses administer vaccines to prevent influenza, providing education and information to those contemplating or receiving the vaccine.

Prevention

The Centers for Disease Control and Prevention recommend that people—particularly the at-risk population such as children, individuals with other diseases or disorders or a compromised immune system, and the elderly—get an influenza vaccine injection each year before the flu season starts. In the United States the flu season typically runs from late December to early March. Vaccines should be received two to six weeks prior to the beginning of the flu season to allow people's bodies enough time to establish immunity. Adults need only one dose of the yearly vaccine, but children under nine years of age who have not previously been immunized should receive two doses with a month between each dose.

Each season's flu vaccine contains three virus strains that are the most likely to be encountered in the coming flu season. When there is a good match between the anticipated flu strains and the strains used in the vaccine, the vaccine is 70–90% effective in people younger than 65 years of age. Because immune response diminishes somewhat with age, people older than 65 years may not receive the same level of protection from the vaccine as do younger people. Even if they do contract the flu, the elderly benefit from vaccines, which diminish severity and help prevent complications.

The virus strains used to make the vaccine are inactivated and will not cause a case of influenza. In the past, flu symptoms following vaccination were associated with vaccine preparations that were not as highly purified as modern vaccines, not to the virus itself. In 1976 there was a slightly increased risk of developing Guillain-Barré syndrome, a very rare disorder associated with the swine flu vaccine. This association occurred only with the 1976 swine flu vaccine preparation and has never recurred.

Serious side effects with modern vaccines are extremely unusual. Some people experience a slight soreness at the point of injection, which resolves within a day or two. People who have never been exposed to influenza, particularly children, may experience one to two days of a slight fever, tiredness, and muscle aches. These symptoms start within 6 to 12 hours after vaccination.

It should be noted that certain people should not receive an influenza vaccine. Infants six months and younger have immature immune systems and will not benefit from the vaccine. Since the vaccines are prepared using hen eggs, people who have severe allergies to eggs or other vaccine components should not receive the influenza vaccine. As an alternative, they may receive a course of amantadine or rimantadine, which are also used as protective measures against influenza. Other people who might receive these drugs are those who have been immunized after the flu season has started or who are immunocompromised, such as people with advanced HIV disease. Amantadine and rimantadine are 70–90% effective in preventing influenza.

Members of certain groups are strongly advised to be vaccinated because they are at-risk for influenza-related complications:

  • • all people 65 years and older
  • • residents of nursing homes and chronic-care facilities, regardless of age
  • • adults and children who have chronic heart or lung problems, such as asthma
  • • adults and children who have chronic metabolic diseases, such as diabetes and renal dysfunction, as well as severe anemia or inherited hemoglobin disorders
  • • children and teenagers receiving long-term aspirin therapy
  • • pregnant women who will be in the second or third trimester during flu season, or women who are nursing
  • • anyone who is immunocompromised, including HIV-infected people with CD4 count over 200; people with cancer ; organ transplant recipients; and people receiving steroids, chemotherapy , or radiation therapy
  • • anyone in contact with people in these groups, such as teachers, care givers, health-care personnel, and family members
  • • travelers to foreign countries

An individual need not be in one of the at-risk categories listed above, however, to receive a flu vaccination. Anyone who wants to avoid the discomfort and inconvenience of a case of influenza should receive the vaccine.


KEY TERMS


Common cold —A mild illness caused by an upper respiratory virus. Usual symptoms include nasal congestion, coughing, sneezing, throat irritation, and a low-grade fever.

Epidemic —A widespread regional disease out-break.

Guillain-Barré syndrome —Also called acute idiopathic polyneuritis, this condition is a neurologic syndrome that can cause numbness in the limbs and muscle weakness following certain viral infections.

Pandemic —Worldwide or multiregional outbreak of an infection afflicting millions of people.

Reye's syndrome —A syndrome of nausea, vomiting, and neurological problems such as confusion or delirium. It can be fatal in children.


Resources

BOOKS

Craighead, John E. Pathology and Pathogenesis of Human Viral Disease. New York: Academic Press, 2000.

Dolin, Raphael. "Influenza." In Harrison's Principles of Internal Medicine, 14th ed. Ed. Anthony S. Fauci et al., New York: McGraw-Hill, 1998, 1096-1098.

Hayden, Frederick G. "Influenza." In Cecil Textbook of Medicine, 21st ed. Ed. Lee Goldman and J. Claude Bennett. Philadelphia: W.B. Saunders, 2000, 1797-1800.

Kolata, Gina B. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It. Carmichael, CA: Touchstone Books, 2001.

Ramen, Fred. Influenza. New York: Rosen Publishing Group, 2001.

Wright, Peter. "Influenza Viruses." In Nelson Textbook of Pediatrics, 16th ed. Ed. Richard E. Behrman et al., Philadelphia: Saunders, 2000, 987-990.

PERIODICALS

Berry, B B, D.A. Ehlert, R.J. Battiola, and G. Sedmak. "Influenza Vaccination Is Safe and Immunogenic when Administered to Hospitalized Patients." Vaccine 19, nos. 25–26 (2001): 3493-3498.

Chisholm, J.C., T. Devine, A. Charlett, C.R. Pinkerton, and M. Zambon. "Response to Influenza Immunization During Treatment for Cancer." Archives of Diseases of Children 84, no. 6 (2001): 496-500.

Fleming, D.M., and M. Zambon. "Update on Influenza and Other Viral Pneumonias." Current Opinions on Infectious Diseases 14, no. 2 (2001): 199-204.

Fleming, D.M. "Managing Influenza: Amantadine, Rimantadine and Beyond." International Journal of Clinical Practice 55, no. 3 (2001): 189-195.

Green, M.S. "Compliance with Influenza Vaccination and the Health Belief Model." Israel Medical Association Journal 2, no. 12 (2001): 912-913.

Hak, E., T.J. Verheij, G.A. van Essen, A. B. Lafeber, D.E. a Grobbee, and A.W. Hoes. "Prognostic Factors for Influenza-Associated Hospitalization and Death During an Epidemic." Epidemiology of Infections 126, no. 2: 261-268.

James, J.S. "Flu Epidemic: Shots, New Treatments Available." AIDS Treatment News no 335 (21 Jan. 2000): 2-4.

Michaeli, D. "Influenza Vaccination." Israel Medical Association Journal 2, no. 12 (2000): 914-915.

Wareing, M.D., and G.A. Tannock. "Live Attenuated Vaccines Against Influenza; An Historical Review." Vaccine 19, nos. 25, 26 (2001): 3320-3330.

ORGANIZATIONS

American Academy of Emergency Medicine. 611 East Wells

Street, Milwaukee, WI 53202. (800) 884-2236. <http://www.aaem.org>.

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007-1098. (847) 434-4000. <http://www.aap.org/default.htm>.

OTHER

Centers for Disease Control and Prevention. <http://www.cdc.gov/ncidod/diseases/flu/fluvirus.htm>.

Food and Drug Administration. <http://www.fda.gov/cder/drug/advisory/influenza.htm>.

National Coalition for Adult Immunization. <http://www.nfid.org/factsheets/influadult.html>.

National Foundation for Infectious Diseases. <http://www.nfid.org/library/influenza>.

National Institute of Allergy and Infectious Diseases. <http://www.niaid.nih.gov/publications/flu.htm>.

National Library of Medicine. <http://www.nlm.nih.gov/ medlineplus/influenza.html>.

World Health Organization. <http://www.who.int/emc/ diseases/flu/>.

L. Fleming Fallon, Jr., M.D., Dr.P.H.

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Influenza

Influenza

Influenza ("the flu") is a disease caused by the influenza virus . The disease is easily spread from person to person, typically by inhaling virus that has been expelled into the air by coughing or sneezing. The virus can also be spread by touch . For example, if someone touches a doorknob that has influenza viruses clinging to it and then touches their mouth, the virus can pass into their body and cause influenza.

The influenza virus infects the nose, throat, and lungs of people. In contrast to the common cold , which is caused by a different virus, the symptoms of the flu develop suddenly. These symptoms include fever, headache and body aches, tiredness, cough, sore throat, and stuffy nose.

Most people who contract the flu recover completely in a few weeks. However, in some people influenza can progress to pneumonia , which can be life threatening. Recovery from influenza does not protect someone from future bouts of the disease. This is because the influenza virus readily changes the expressions of its genetic material (i.e., it mutates readily). Thus, the influenza virus that the body's immune system responds to one season may be different from the virus that infects the body some months later.

Influenza is a common illness. For example, every year approximately 25 to 50 million Americans (about 10–20% of the population of the United States) contract influenza. Of these, about 20,000 people die of the infection , and 114,000 require hospitalization.

There are three types of influenza virus. All three are in the viral group called Orthomyxovirus. The three viral types are called influenza A, B, and C. Influenza A and B cause large numbers of cases of the flu almost every winter, when people are confined indoors and spread of the virus is easier.

Influenza A is further divided into two subtypes called hemagglutinin (H) and neuraminidase (N). H and N are two proteins that are found on the surface of the filament-like virus particles. They both protrude from the surface and appear as spikes when viruses are examined under high magnification. The protein spikes function to help the virus invade host cells.

Influenza viruses are resident in animals and birds including pigs , horses , seals , whales, a variety of wild birds, and ducks . The virus can spread from this reservoir to humans.

Influenza has been part of mankind for millennia. In the twentieth century, there were a number of large outbreaks. For example, in 1918–1919 the "Spanish flu" killed more than 500,000 people in the United States and up to 50 million people around the world. The influenza virus that caused this outbreak was very deadly. Concerns have been raised that the same virus could establish another epidemic .

In 1957–1958 the "Asian flu" caused 70,000 deaths in the United States. The same virus remains in circulation today. In 1968–1969, an outbreak of what was dubbed the "Hong Kong flu" killed approximately 34,000 Americans. In 1976, a small outbreak affected soldiers at a military base in Fort Dix, New Jersey. Experts predicted that the influenza, which was known as the "Swine flu," could spread throughout the United States. The subsequent public concern bordered on hysteria, and prompted a vaccination campaign in which 40 million Americans were vaccinated. The outbreak did not materialize.

Vaccination is not a guarantee that all types of influenza will be prevented. Rather, influenza is typically dealt with after it appears. Flu is treated with rest and fluids. Maintaining a high fluid intake is important, because fluids increase the flow of respiratory secretions that may prevent pneumonia. Antiviral medications such as amantadine and rimantadine may be prescribed for people who have initial symptoms of the flu and who are at high risk for complications. This medication does not prevent the illness, but reduces its duration and severity.

A flu vaccine is available that is formulated each year against the current type and strain of flu virus. The
virus is grown in chicken eggs, extracted, and then rendered noninfective by chemicals. The vaccine is also "updated" to the current viral strain by the addition of proteins that match the protein composition of the influenza virus type that is currently circulating in a population. The vaccine would be most effective in reducing attack rates if it was effective in preventing influenza in schoolchildren; however, in vaccine trials the vaccine has not been shown to be effective in flu prevention in this age group. In certain populations, particularly the elderly, the vaccine is effective in preventing serious complications of influenza and thus, lowers mortality.

Vaccine research is ongoing. One of the more exciting advances in flu vaccines involves research studies examining an influenza vaccine mist, which is sprayed into the nose. This is predicted to be an excellent route of administration, which will confer even stronger immunity against influenza. Because it uses a live virus, it encourages a strong immune response. Furthermore, it is thought to be a more acceptable immunization route for schoolchildren, who are an important reservoir of the influenza virus.

See also Aerosols; Cold, common.


Resources

books

Kolata, G.B. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It. New York: Farrar Straus & Giroux, 1999.

Potter, C.W. Influenza London: Elsevier Health Sciences, 2002.

organizations

Centers for Disease Control and Prevention, 1600 Clinton Road, Atlanta, GA 30333 (404) 639–3311. July 29, 2002 [cited November 12, 2002] <http://www.cdc.gov/ncidod/diseases/flu/fluinfo.htm.


Brian Hoyle

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