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Pneumocystis
carinii is a common organism that may reside harmlessly in normal lungs. It generally causes pneumonia only when the body's defenses are weakened because of cancer, cancer treatment, or AIDS. Often, it is the first indication that a person with human immunodeficiency virus (HIV) infection has developed AIDS.
Most people develop a fever, shortness of breath, and a dry cough. These symptoms usually arise over several weeks. The lungs may not be able to deliver sufficient oxygen to the blood, leading to severe shortness of breath.
X-rays show either no abnormality or patchy infection, similar to what is seen in some viral infections. The diagnosis is made by microscopic examination of a sputum specimen obtained by one of two techniques—sputum induction (in which a vapor is used to stimulate coughing) or bronchoscopy (in which an instrument is inserted into the airways to collect a specimen (see Symptoms and Diagnosis of Lung Disorders: Bronchoscopy)).
The combination antibiotic trimethoprim-sulfamethoxazole can be used to help prevent pneumocystis pneumonia in people at risk. This drug's side effects, which are particularly common in people who have AIDS, include rashes, a reduced number of infection-fighting white blood cells, and fever. Alternative preventive drug treatments are dapsone, atovaquone, and pentamidine (which can be taken as an aerosol, inhaled directly into the lungs).
Drugs used to treat pneumocystis pneumonia are trimethoprim-sulfamethoxazole, dapsone combined with trimethoprim, clindamycin and primaquine, atovaquone, or intravenous pentamidine. When blood oxygen pressure falls below a certain level, corticosteroids may also be given.
Even when the pneumonia is treated, the overall death rate is 15 to 20%.
Last full review/revision February 2003
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