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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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