Pneumonia
Pneumonia
Disease History, Characteristics, and Transmission
Introduction
Pneumonia is an inflammatory response of the lungs to the entry of an infective organism or other foreign material. It is an important disease, as it is the sixth leading cause of death in the United States, and the major cause of death from infection.
Pneumonia is a complex disease with many different causes and risk factors. It can affect people of any age, anywhere, although the very young and the very old are most vulnerable to an attack. Pneumonia is classified in two ways—according to its cause and according to its setting.
The cause of pneumonia can be viral, bacterial, mycobacterial, fungal, or even non-infective irritants.
The setting may be either within the community or in the hospital. These distinctions are important because they influence the choice of treatment. Before the advent of antibiotics, pneumonia was a greatly feared disease because it could kill so easily. Today, with effective treatment, most people can expect to make a full recovery from pneumonia.
Disease History, Characteristics, and Transmission
Pneumonia is unlike many other infectious diseases in that it cannot be attributed to infection by one, or just a few, specific microbes. The respiratory tract, consisting of the nose, pharynx (back of the throat), trachea (windpipe), and lungs, has various mechanisms to protect itself from microbes as well as foreign bodies, such as particulate pollution, food, liquid, or gas. The nose and trachea are lined with mucous membranes, which bear tiny beating hairs called cilia. The thick mucous traps any microbes or foreign particles as they enter through the nose and mouth and the cilia propel them back to the nose and mouth where they are expelled, by nose blowing, or are swallowed. This mechanism protects the bronchi, which are the tiny tubes fanning out to connect the trachea with the alveoli, the tiny air sacs making up the lung tissue.
The cough reflex is another of the lungs’ defenses against infection, expelling foreign material before it enters the lungs. Added to this is the immune system, which will trigger cells or antibodies to destroy any threatening microbes or other material. Therefore, microorganisms may colonize the upper part of the respiratory tract, without causing disease, or they may cause an infection such as a cold or influenza. With the usual defenses in place, they do not invade the lungs.
If these defenses break down for any reason—for instance, because of the use of a mechanical ventilator in the intensive care unit, or because of weakened immunity—infection may spread down to the lungs. The alveoli mediate gas exchange between the lungs and the blood—oxygen in, carbon dioxide out. They deal with anything that threatens this function, such as invading microbes or particulate matter, with a strong inflammatory response, which is the underlying mechanism of pneumonia. One of the main features of this inflammation is the production of a thick secretion or exudate by the lung tissue.
Over 100 different organisms can cause pneumonia, and the most significant of these depends on patient characteristics and the setting—whether in the community or in the hospital. Some of the most important viral causes of pneumonia include adenovirus, respiratory syncytial virus, influenza virus, parainfluenza virus, and cytomegalovirus. Among the bacteria that can cause pneumonia are Streptococcus pneumoniae, Chlamydia pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Mycoplasma, which are organisms that have some of the characteristics of both bacteria and viruses, can also cause pneumonia.
Among AIDS patients, Pneumocystis carinii is a major cause of pneumonia as an opportunistic infection. Before the advent of AIDS, P. carinii pneumonia was rare and its sudden appearance alerted researchers to the emergence of a new disease. P. carinii is a fungus-like organism. Other fungi that cause pneumonia include Histoplasma capsulatum and Cryptococcus neoformans.
Pneumonia may follow an attack of influenza or even a cold, but it can also arise on its own. Anyone who suddenly starts to feel worse after flu or a cold needs to get medical advice immediately. The symptoms of pneumonia vary from mild to very severe, and they may be either gradual or sudden in onset. The nature of the symptoms also varies depending upon the infecting microbe and patient characteristics. A cough, which may be either dry or productive of green or rust-colored phlegm (a discharge from the lungs), is probably the most common symptom of pneumonia. Sometimes the patient will even cough up blood. Fever, chills, and breathlessness may also occur and there may be chest pain. However, older people may have few symptoms other than mental confusion.
Bacterial pneumonia tends to come on suddenly with fever, shaking chills, sweating, and chest pain. The cough usually produces thick greenish or yellow phlegm. The symptoms are usually more dramatic among those previously in good health.
In viral pneumonia, which is more common in the winter months, there is a dry cough, headache, fever, muscle pain, and fatigue. Breathlessness tends to develop as the disease goes on and the cough starts to produce white phlegm. Viral pneumonia is a particular threat to those with pre-existing heart or lung disease. If it does not clear up, a secondary bacterial pneumonia may take hold.
Mycoplasma pneumonia is sometimes called “walking pneumonia” because the symptoms are gradual and mild—indeed, patients are not always aware that they are ill. This form of pneumonia often strikes schoolchildren and young adults. It may account for up to one-third of all childhood cases.
The examining doctor will look for signs of pneumonia, such as an increase in respiration and pulse rate. Pneumonia also is associated with characteristic chest sounds—bubbling, cracking sounds called rales, and rumblings called ronchi—that indicate the presence of fluid within the alveoli. These can be heard when the doctor puts a stethoscope to the chest. Chest x-ray, and possibly computed tomography (CAT) scanning, are an important part of the diagnosis of pneumonia, since they will reveal characteristic opacities or shadows on the affected lung. (Pneumonia may affect one or both lungs.)
The complications of pneumonia include blood poisoning, pleural effusion, and lung abscess. The alveoli are in close contact with the bloodstream and so the infection may enter the bloodstream, causing what is commonly known as blood poisoning or septicemia. When bacteria enter the bloodstream, they can reach the other organs of the body in a short time, possibly resulting in multi-organ failure and death. In pleural effusion, fluid leaks from the lungs into the space between the pleura, which are the membranes covering the lungs and the inner surface of the chest wall. This fluid could become infected—a condition known as empyema—and may have to be drained or removed surgically. Finally, an abscess, which is a cavity containing pus-infected material, may form within the lungs as a result of pneumonia. Although treatable with antibiotics, a lung abscess occasionally must be removed surgically.
WORDS TO KNOW
ANTIBIOTIC RESISTANCE: The ability of bacteria to resist the actions of antibiotic drugs.
ASPIRATION: Aspiration is the drawing out of fluid from a part of the body; it can cause pneumonia when stomach contents are transferred to the lungs through vomiting
CILIA: Cilia, which are specialized arrangements of microtubules, have two general functions. They propel certain unicellular organisms, such as paramecium, through the water. In multicellular organisms, if cilia extend from stationary cells that are part of a tissue layer, they move fluid over the surface of the tissue.
NOSOCOMIAL: A nosocomial infection is an infection that is acquired in a hospital. More precisely, the Centers for Disease Control and Prevention in Atlanta, Georgia, defines a nosocomial infection as a localized infection or one that is widely spread throughout the body that results from an adverse reaction to an infectious microorganism or toxin that was not present at the time of admission to the hospital.
OPPORTUNISTIC INFECTION: An opportunistic infection is so named because it occurs in people whose immune systems are diminished or are not functioning normally; such infections are opportunistic insofar as the infectious agents take advantage of their hosts’ compromised immune systems and invade to cause disease.
The complications of pneumonia are more common among the elderly, the frail, and those with weakened immunity, such as HIV/AIDS patients. The prognosis of pneumonia depends upon the setting and the patient. In those over 65, mortality ranges from 5% to 65%. The overall death rate for community-acquired pneumonia (CAP) is less than 1%. This rises to around 14% for nosocomial or hospital-acquired pneumonia (HAP) and to around 40% for patients in the intensive care unit.
Pneumonia is not transmitted from one person to another. Instead, it involves aspiration of microbes into the lungs from a previously colonized airway, implying that the normal defense mechanisms of the respiratory tract have broken down for some reason. It can also develop through aspiration of stomach contents, gas, or particulate pollution, all of which may inflame lung tissue.
Scope and Distribution
The public health burden of pneumonia in the United States is considerable. There are three million cases of pneumonia each year, accounting for ten million physician visits, 600,000 hospital admissions, and more than 60,000 deaths. It is the sixth most common cause of death and the leading cause of death from infection. Pneumonia accounts for half of all deaths from infection in the United States. Worldwide, pneumonia is the leading cause of death among infants less than one year old.
Pneumonia can strike at any age, but infants and children under four years of age and those over 65 years old are most at risk. The elderly account for almost 90% of all deaths from pneumonia and influenza. In adults, strong risk factors for pneumonia include existing illnesses such as congestive heart failure, kidney disease, diabetes, chronic obstructive pulmonary disease, removal of the spleen, malnutrition, alcoholism, institutionalization, and dementia. Children and young adults with cystic fibrosis are especially at risk of pneumonia. For infants, low birth weight and low maternal age have been found to be risk factors for pneumonia.
Community-acquired pneumonia (CAP) refers to pneumonia contracted outside a hospital setting—that is, either at home in the community or in a nursing home, day care setting, school, or other place where people congregate. The cause of CAP is often viral, but bacteria are also important causes of CAP. Different species of bacteria are involved in causing CAP in different age groups. Streptococcus and pneumococcus are the most common causes of pneumonia, accounting for up to 35% of all cases. Streptococcus and Staphylococcus species of bacteria are found to be especially important in cases of pneumonia in newborns, while S. pneumoniae and H. influenzae infections are common in older children. S. pneumoniae infection is also found often in elderly people with pneumonia.
Hospital-acquired pneumonia (HAP) is one of the most significant nosocomial infections. It refers to pneumonia that develops 48 hours after hospital admission. HAP occurs at a rate of 5–10 per 1,000 hospital admissions in the United States. Most cases occur in the intensive care unit or in post-surgical recovery. The risk of HAP is 6–20 times greater among those on mechanical ventilation. This is because ventilation involves inserting a tube into the trachea, which disrupts the natural defenses of the respiratory tract. The microbiology of HAP has been found to differ from that of CAP with Klebsiella pneumoniae, Pseudomonas aeruginosa, Serratia, and Enterobacter species, all of which are gram-negative bacilli, being most often involved. The term gram-negative (or positive) refers to the way a bacterial species reacts with a common stain used in microscopic studies.
IN CONTEXT: DISEASE IN DEVELOPING NATIONS
Pneumonia is an infection of the lung that can be caused by nearly any class of organism known to cause human infections, including bacteria, viruses, fungi, and parasites. In the United States, pneumonia is one of the most common diseases leading to death, and the most common fatal infection acquired by already hospitalized patients. In developing countries, pneumonia and diarrhea are the most common causes of death.
Treatment and Prevention
Some cases of pneumonia need to be treated in the hospital and prompt assessment by a physician is needed, because the condition can progress rapidly. An increased respiratory rate, decreased blood pressure, increased temperature, and confusion are all potential indicators for hospital admission. Microbiological tests are often needed to confirm the infective organism.
However, the physician often needs to start empiric antibiotic treatment before the microbiology results are available. There is no effective treatment for viral pneumonia, which usually clears up on its own. In particular, antibiotics will not work against viruses. For those recovering from pneumonia at home, bed rest is important, along with plenty of fluids to help loosen mucus in the lungs. These patients should also be sure to stay away from those with weakened immunity, which may mean not visiting anyone in the hospital.
Many different antibiotics can be used to treat pneumonia. The American Thoracic Society has established guidelines to help physicians make a good choice of antibiotic for pneumonia, based upon the patient and the setting. For out-patients, amoxicillin, azithromycin, and levofloxacin are often used. The latter is one of a relatively new group of drugs called the respiratory fluoroquinolones, which are valuable because they can treat drug-resistant bacteria. In-patients not in intensive care may be given cefotaxime, while intensive care patients may be treated with a combination of drugs, such as cefotaxime with a fluoroquinolone. Sometimes treatment is given by injection, to get to the infection as quickly as possible. Patients with cystic fibrosis often need high doses of antibiotics and in combination.
Immunization against H. influenzae and pneumococcus is valuable in the prevention of CAP in the over65s and in those otherwise at risk, such as patients with cystic fibrosis. The latter protects against 23 different types of pneumococcus. HAP is preventable by good hospital hygiene, especially relating to mechanical ventilation. Elevation of the bed has been found useful in protecting the lower respiratory tract from infection. Prevention of pneumonia is important, because the complications of the condition can be so serious. And with the growth of drug-resistant strains of bacteria that can cause pneumonia, effective treatment can no longer be relied upon.
Impacts and Issues
William Oster, the great nineteenth century Canadian physician, called pneumonia “the old man's friend” because it often releases an elderly, frail, terminal patient from a catalog of severe medical complaints. However, not all patients with pneumonia fall in this category. HAP is the second most common nosocomial infection in the United States and the most serious in terms of morbidity and mortality, with 300,000 new cases a year, accounting for 1.2 billion U.S. dollars in healthcare costs.
The causes of HAP need addressing when they are preventable, such as violations in infection control, including insufficient handwashing, and the use of equipment that could be contaminated. However, the risk of HAP is inextricably linked to the nature of modern medicine, especially when it comes to intensive care. Mechanical ventilation may save the lives of the desperately ill, but it is also the leading cause of HAP because of the way in which it breaches the natural defenses of the respiratory tract against infection. Other invasive devices that are linked with a high risk of HAP include nasogastric intubation (a tube leading from the nasal passages to the stomach) for feeding an unconscious patient, and chest, abdominal, and head and neck surgery. Again, these can be life saving treatments, and health care workers and researchers are attempting to develop technologies and practices within the intensive care and surgical setting that can minimize the risk of pneumonia.
Another major concern arising from HAP is that the cause is often a multi-drug resistant organism. This means that the patient's upper respiratory tract has been colonized with such a resistant organism and it may be difficult to find an antibiotic within the armory available to the physician that can treat the pneumonia successfully. Antibiotic resistance is also a concern in CAP, as penicillin-resistant S. pneumoniae is increasingly common. The fight against antibiotic resistance is two-fold. Researchers must develop new classes of antibiotic, which act by mechanisms not previously known. And both existing and new antibiotics must be used sparingly. Overuse or misuse of antibiotics promotes the emergence of resistant strains. On exposure, the weaker strains die, leaving the more resistant ones to flourish. This is especially likely to happen when a patient does not finish a prescribed course because symptoms of the infection clear up. This is as true of pneumonia as of any other infection. Patients must be responsible and take their medication exactly as prescribed. Only then are the chances of killing resistant bacteria maximized.
Primary Source Connection
In the following journal article, author Carol Potera discusses a type of aspiration (inhalation) pneumonia seen after the 2004 Asian tsunami that was termed “tsunami lung.” Potera is a contributor to Environmental Health Perspectives, a journal devoted to the interaction between environmental factors and human and animal health.
In Disaster's Wake: Tsunami Lung
When the Asian tsunami struck on 26 December 2004, health authorities braced for an onslaught of waterborne illnesses including malaria and cholera, which often follow such disasters. But saltwater flooded the freshwater breeding grounds of the mosquitoes that spread malaria, and relief agencies quickly distributed bottled water, thwarting a cholera epidemic. Instead, a type of aspiration pneumonia named “tsunami lung” emerged and afflicted some survivors.
Tsunami lung occurs when people being swept by tsunami waves inhale saltwater contaminated with mud and bacteria. The resulting pneumonia-like infections normally are treated with antibiotics. However, the 2004 tsunami “wiped out the medical infrastructure, and anti-biotics were not available to treat infections in the early stages,” says David Systrom, a pulmonologist at Massachusetts General Hospital in Boston. Consequently, victims’ lung infections festered, entered the bloodstream, and spread to the brain, producing abscesses and neurological problems such as paralysis.
Systrom and colleagues volunteered to work on a medical disaster team with Project HOPE (Health Opportunities for People Everywhere) aboard the hospital ship U.S. Naval Ship Mercy off the coast of Banda Aceh, Sumatra. When they arrived three weeks after the tsunami hit, “we saw infections not seen in the United States since before the development of antibiotics,” says Systrom. Among them were about 25 cases of tsunami lung. “No one expected the number of tsunami lung cases we saw,” says Systrom. “It was not on the radar screen.”
The diagnosis of tsunami lung requires a chest radiograph and computed tomography scan of the brain to confirm abscesses. This sophisticated equipment was available on the hospital ship. “Only the most severe cases with central nervous system involvement made it to the ship,” says Systrom. The team suspects that hundreds of milder cases went unreported.
In the 23 June 2005 issue of the New England Journal of Medicine, the team describes the case of a 17-year-old girl who aspirated water and mud while engulfed by a wave and carried about half a mile. She developed pneumonia two weeks later and was treated at a local clinic with unknown medicines. A week later, the right side of her face drooped, her right arm and leg became paralyzed, and she stopped talking.
A chest radiograph revealed air and pus outside the lining of the lung (a condition known as hydropneumothorax), and a brain scan showed four abscesses. After the doctors treated her with a combination of intravenous antibiotics (imipenem until the stock of that drug ran out, then vancomycin, ceftazadime, and metronidazole), her speech and facial movement recovered first. When she moved her right leg and arm for the first time, she “burst into peals of laughter,” according to the report. She was transferred to an International Committee of the Red Cross-Crescent field hospital. “I suspect she'll fully recover,” says Sydney Cash, a neurologist at Massachusetts General Hospital and member of the team, who has since received pictures of her walking.
A combination of microbes likely contributes to tsunami lung, but no lab facility was available to culture and identify those found in the Indonesian patients before the Mercy arrived. However, in a letter published in the 4 April 2005 issue of the Medical Journal of Australia, Anthony Allworth, director of infectious diseases at Royal Brisbane and Women's Hospital, describes culturing Burkholderia pseudomallei from two tsunami lung patients in a land-based hospital and Nocardia species from a third.
B. pseudomallei lives in the Asian soil and water. Mark Pasternack, an infectious disease specialist at Massachusetts General Hospital who also served on the Mercy, says, “You do not have to directly aspirate Burkholderia to produce pneumonia…. After the tsunami, people had soft tissue injuries from being forced into objects, so they could have gotten Burkholderia from wounds or aspiration.”
Cash echoes this thought: “Natural disasters produce odd combinations of pathogens and unexpected ways for the body to be damaged that lead to unexpected clinical circumstances. [Medical disaster physicians need to] keep an open mind and expect the unexpected.”
Could an infection like tsunami lung emerge in victims of Hurricane Katrina? Probably not, speculates Pasternack. Although the water sweeping the Gulf Coast area may have been contaminated, “it was not forced down peoples’ lungs by high-speed waves,” he says. Therefore, aspiration pneumonia and its complications are unlikely to appear commonly during the Gulf Coast relief efforts.
Carol Potera
POTERA, CAROL. “IN DISASTER'S WAKE: TSUNAMI LUNG.” ENVIRONMENTAL HEALTH PERSPECTIVES 113 (2005): 11, 734.
See AlsoChlamydia pneumoniae; Haemophilus influenzae; MRSA; Nosocomial (Healthcare-Associated) Infections; Pneumocystis carinii Pneumonia.
BIBLIOGRAPHY
Books
Gates, Robert H. Infectious Disease Secrets. 2nd ed. Philadelphia: Hanley and Beltus, 2003.
Tan, James S. Expert Guide to Infectious Diseases. Philadelphia: American College of Physicians, 2001.
Wilson, Walter R., and Merle A. Sande. Current Diagnosis & Treatment in Infectious Diseases. New York: McGraw Hill, 2001.
Web Sites
American Lung Association. “Pneumonia Fact Sheet.”
April 2006. <http://www.lungusa.org/site/apps/nl/content3.asp?c=dvLUK9O0Eb=2060321content_id={08C669B0-E845-4C9C-8B1E-285348BC83BD}notoc=1> (accessed March 25, 2007).
Mayo Clinic. “Pneumonia.” May 12, 2005. <http://www.mayoclinic.com/health/pneumonia/DS00135> (accessed March 25, 2007).
Susan Aldridge