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Pneumocystis carinii pneumonia

Pneumocystis carinii pneumonia (PCP) is a form of pneumonia which is caused by protozoa called Pneumocystis carinii, which belong to the Apicomplexa. It is relatively rare in normal, immunocompetent people but common among people infected with HIV (the virus which causes AIDS). In that population, before the advent of effective treatment, it was a common immediate cause of death, and can still be the first indication of AIDS, though it does not generally occur unless the CD4 count is less than 200/mm³.


high fever; cough; shortness of breath, especially on exertion; weight loss; night sweats; sputum production


The clinical diagnosis can be confirmed by the characteristic appearance of the chest x-ray which shows widespread infiltrates, and an arterial oxygen level (pO2) strikingly lower than would be expected from symptoms. The diagnosis can be definitively confirmed by pathologic identification of the causative organism in bronchial washings obtained by bronchoscopy.


Antipneumocystic medication is used with concomitant steroids in order to avoid inflammation that causes an exacerbation of symptoms which typically appears four days after treatment begins if steroids are not used. By far the most commonly used medication is trimethoprim/sulfamethoxazole; other medications that are used, alone or in combination, include pentamidine, trimetrexate, dapsone and clindamycin. Treatment is usually for a period of about 21 days.

Much of the incidence of PCP has been reduced by instituting a standard practice of using oral trimethoprim/sulfamethoxazole to prevent the disease in people with CD4 counts less than 200/mm³.