Pneumocystis carinii pneumonia (PCP) is a form of pneumonia which is caused by a microorganism called Pneumocystis carinii (It has been proposed that the organism be renamed Pneumocystis jiroveci). 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.

Symptoms

Symptoms of PCP include high fever, non-productive cough, shortness of breath (especially on exertion), weight loss and night sweats. Sputum production is usually not marked with PCP unless the patient is co-infected with a bacterial superinfection. The fungus can invade other visceral organs, such as the liver, spleen and kidney, but only in a minority of cases.

Diagnosis

The clinical diagnosis can be confirmed by the characteristic appearance of the chest x-ray which shows widespread pulmonary 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.

Treatments

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 a combination of trimethoprim and sulfamethoxazole (co-trimoxazole, with the tradenames Bactrim or Septrin). 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.