Pneumocystis carinii: A review of an important opportunistic pathogen in AIDS.

Since the first report of human infection with Pneumocystis carinii in 1942, cases of pneumonia due to this opportunistic pathogen have become increasingly common. Animal studies and clinical observations show that a significant depletion or dysfunction of T helper lymphocytes predisposes to clinical disease. Individuals with damaged T helper cells secondary to malignancies (eg, Hodgkin's lymphoma), drugs (eg, cyclosporine, steroids), or certain infections (eg, human immunodeficiency virus) are at particular risk. Serological studies suggest that disease is most often secondary to the reactivation of an asymptomatic infection, usually acquired during childhood. Increasing shortness of breath, a nonproductive cough and hypoxia often preceded by several weeks of lethargy, fever and weight loss are the classical features of P carinii pneumonia in acquired immune deficiency syndrome. Bronchoalveolar lavage is usually the optimal diagnostic test. Immunofluorescent staining on liquified sputum induced by nebulized saline appears to be a promising and noninvasive test. Early empiric therapy with trimethoprim-sulphamethoxazole (trimethoprim 5 mg-sulphamethoxazole 25 mg/kg/day every 6 h) or intravenous pentamidine (4 mg/kg/day) for 21 days is usually effective, but infection is not eradicated, and clinical disease is likely to recur. Prophylaxis using aerosolized pentamidine reduces the risk of pulmonary disease but can predispose to extrapulmonary infection. Improved in vitro and in vivo models of human pneumocystis infection would significantly increase understanding of the molecular biology of the organism, the pathogenesis of disease, and the optimal therapeutic regimens.