PNEUMONIA

DEFINITION

Pneumonia (pronounced noo-MOAN-ya) is an infection of the lung. It can be caused by a great many different agents, including bacteria, viruses, fungi, and parasites. In the United States, pneumonia is the sixth most common disease leading to death. It is also the most common fatal infection acquired by patients in hospitals. In developing countries, pneumonia is one of the two most common causes of death. Diarrhea is the other.

DESCRIPTION

The healthy human lung is normally free of disease-causing microorganisms, such as bacteria and viruses. The body has immune system (a complex defense system) is designed to keep it that way. For example, hairs in the nose trap large particles carried along by the air we breathe in. The epiglottis is a kind of trapdoor in the larynx (windpipe; pronounced LAYR-inx) that keeps food and other swallowed substances from entering the lungs. Mucus, a thick liquid, is produced throughout the respiratory (breathing) system to capture dust, bacteria, and other organisms. Cilia (pronounced SIL-ee-uh) are hairlike projections along the lining of the respiratory system that also trap and remove foreign objects from the body. Special types of white blood cells, called macrophages (pronounced MAK-ruh-faj), are also part of this defensive system. They are produced when foreign bodies enter the body to attack and destroy those bodies.

This system of defenses does not work perfectly, however. Sometimes organisms that can cause infection get into the lungs. For example, a person may be exposed to large amounts of smoke. There may be too many smoke particles for the body's defense system to remove. In such a case, the lungs may become infected and pneumonia can develop. the airways.

Conditions that Lead to Pneumonia

In many cases, the lungs become infected simply because they are overwhelmed with some foreign agent, such as bacteria or smoke particles. But a variety of conditions can increase the likelihood that a person will contract (catch) pneumonia. In these conditions, the person's lungs may already be weakened or damaged by some other problem. Some of these conditions include the following:

• Damage to the epiglottis. Stroke, seizures, alcohol, and various drugs can prevent the epiglottis from functioning normally. When this happens, materials that have been swallowed may get into the lungs, causing an infection there.
• Viruses. Viruses can damage the cilia that line the respiratory tract. Foreign bodies may then get into the lungs more easily, causing an infection. One such virus is HIV (the human immunodeficiency virus), which causes AIDS (see AIDS entry). Pneumonia is a major health problem for people with AIDS and those who have HIV in their bodies.
• Old age. As people grow older, their immune systems often become weaker. They are less able to fight off infections that once would not have been a problem.
• Chronic diseases. A chronic disease lasts for a very long time, usually many years. Examples of such diseases are asthma (see asthma entry), cystic fibrosis (see cystic fibrosis entry), and diseases of the nervous and muscular systems. These diseases often affect the epiglottis. A damaged epiglottis allows food and contaminated objects to get into the lungs, causing infections that can lead to pneumonia.
• Surgery. Pneumonia is a common complication of surgery. Some drugs used during surgery affect a person's normal breathing pattern. He or she may not be able to cough or breathe as deeply as usual. Foreign objects are not expelled from the respiratory tract. They may get into the lungs and cause an infection.

CAUSES

The list of organisms that can cause pneumonia is very long. It includes bacteria, viruses, fungi, and parasites. Some examples include:

• Viruses are the most common cause of pneumonia in young children. These viruses also cause other infections of the respiratory system, such as influenza (see influenza entry), tonsillitis (see tonsillitis entry), and the common cold (see common cold entry).
• Bacteria are the primary cause of pneumonia in older children and adults. The most common of these bacteria are Streptococcus pneumoniae, (pronounced STREP-tuh-coc-us noo-MOHN-ee-ay) Haemophilus influenzae, (pronounced HEE-mof-uh-lus in-floo-EN-zay) and Staphylococcus aureus (pronounced STAFF-lo-coc-us or-ee-us).
• An organism called Mycoplasma pneumoniae affects older children and adults. The organism is somewhat similar to both bacteria and viruses. It produces a form of pneumonia known as "walking pneumonia."
• A protozoan (one-celled organism) called Pneumocystis carinii causes a form of pneumonia in people with weakened immune systems. The condition, pneumocystis carinii pneumonia (PCP), is one of the most serious medical problems for people with HIV or AIDS. It also affects people whose immune systems have been weakened by chemotherapy or cancer.
• An organism known as Chlamydia psittaci causes a form of pneumonia sometimes known as "bird pneumonia." The disease is quite rare and was once observed only in humans who came into contact with bird droppings. People infected with HIV are also susceptible to the infection.
• In 1976, a new form of pneumonia was discovered. It broke out among a large group of people attending an American Legion convention. The infection was caused by a previously unknown organism. Subsequently named Legionella pneumophila, it causes what is now called Legionnaires' disease. The organism was eventually traced to the air conditioning units at the hotel where the convention took place.

X ray showing pneumonia in the right lung. (Reproduced by permission of the

National Audubon Society Collection/Photo Researchers, Inc.

)

SYMPTOMS

The primary symptoms of pneumonia are fever, chills, cough, chest pain, and shortness of breath. The patient often coughs up sputum (pronounced SPYOO-tum; usually made up of saliva, mucus, dead cells, and other materials) that may be streaked with pus or blood. In the severest cases, a patient shows signs of cyanosis (pronounced SI-uh-no-sis). Cyanosis is caused when a patient's blood is not getting enough oxygen. It is characterized by a blue tint on the nail beds or lips.

DIAGNOSIS

Pneumonia can usually be diagnosed on the basis of a patient's symptoms. A doctor will also listen to the patient's chest with a stethoscope. If the lungs are infected, they produce an unusual sound when the patient breathes in and out. Tapping on the patient's back is also a test for pneumonia. Normally, the tapping produces a hollow sound because the lungs are filled with air. If pneumonia is present, however, the lungs may contain fluid. In this case, the sound is dull thump.

Some forms of bacterial pneumonia can be diagnosed by laboratory tests. A sample of the patient's sputum is taken. The sample is then stained with dyes and examined under a microscope. The organisms causing the disease can often be seen and identified.

X rays can also be used to diagnose pneumonia. Dark spots on the patient's lungs may indicate the presence of an infection. The appearance of the spots may give a clue to the type of infection that has occurred.

TREATMENT

At one time, many cases of pneumonia were fatal. The discovery of antibiotics changed that. Today, many cases of bacterial pneumonia can be cured. Antibiotics are given as soon as the infection is diagnosed.

Viral pneumonia is more difficult to cure. There are not many drugs that kill viruses. Amantadine (pronounced uh-man-tu-deen, trade name Symmetrel) and acyclovir (pronounced a-SI-kloh-veer) are two exceptions. They are sometimes helpful in treating some forms of viral pneumonia.

PROGNOSIS

The prognosis for pneumonia varies widely depending on the type of infection. The recovery rate is nearly 100 percent, for example, in cases of "walking pneumonia." By contrast, people with pneumonia caused by Staphylococcus pneumoniae stand only a 60 percent to 70 percent chance of survival. For the most common form of pneumonia, caused by Streptococcus pneumoniae, the survival rate is about 95 percent.

People who are very young or very old are likely to experience complications from pneumonia. Their immune systems may not be completely healthy. Their bodies may find it difficult to fight off infections related to those that cause pneumonia.

Pneumonia can also lead to other complications that are more serious than the original infection. People with chronic illnesses, such as cirrhosis of the liver or congestive heart failure, or who have weakened immune systems are especially at risk for such complications.

PREVENTION

Pneumonia often develops as a complication following an attack of influenza. To protect against this possibility, a person should be vaccinated against influenza each year. This advice is especially important for elderly people and people who live in crowded conditions, such as nursing homes or army camps.

A vaccine has been developed against Streptococcus pneumoniae. It works very well and is recommended for patients with chronic illnesses.

One consequence of the AIDS epidemic was the development of a new treatment for PCP. Patients may be put on a regular schedule of the drug trimethoprim sulfate and/or inhaled pentamidine. This treatment has dramatically reduced the rate of deaths from PCP among people with AIDS.

FOR MORE INFORMATION

Books

Stoffman, Phyllis. The Family Guide to Preventing and Treating 100 Infectious Diseases. New York: John Wiley & Sons, 1995.

Periodicals

Brody, Jane E. "Pneumonia Is Still a Killer." New York Times (January 8, 1997): pp. B10+.

Organizations

American Lung Association. 1740 Broadway, New York, NY 10019. (800) LUNG–USA. http://www.lungusa.org.

Web sites

"Ask NOAH About: Pneumonia." NOAH: New York Online Access to Health. [Online] http://www.noah.cuny.edu/respiratory/pneumonia.html (accessed on October 26, 1999).

"Pneumonia." Yahoo! Health. [Online] http://health.yahoo.com/health/Diseases_and_Conditions/Disease_Feed_Data/Pneumonia (accessed on October 28, 1999)

"Pneumonia." American Lung Association. [Online] http://www.lungusa.org/diseases/lungpneumoni.html (accessed on October 28, 1999).

Pneumonia.Net. [Online] http://www.pneumonia.net/ (accessed on October 28, 1999).