Pneumocystis carinii infection in human immunodeficiency virus-positive patients

Pneumocystis carinii is a ubiquitous, atypical unicellular fungus. P. carin ii pneumonia (PCP) is responsible for considerable morbidity and mortality in acquired immune deficiency syndrome (AIDS) patients, and is the leading complication in advanced human immunodeficiency virus (HIV) infection. Man! different host (mammal)-specific species of Pneumocystis exist, but the li fe-cycle is not understood fully. Human strains are designated as P. carini i f. sp. (special form) hominis (at least 59 different types). P. carinii i s spread via the airborne route. Disease is most frequently caused by fresh exposure to a source of P. carinii, rather than by reactivation of latent infection. Asymptomatic carriage among healthy persons may occur. PCP occur s in HIV-infected patients when the CD4(+) count falls below a certain thre shold; organisms multiple and gradually fill the alveoli. Symptoms, which i nclude a mildly productive cough, progressive dyspnoea and fever, may persi st fur months prior to diagnosis. Without treatment, progressive respirator y insufficiency invariably ends in death. Pulmonary specimens may be obtain ed by procedures of varying sensitivity and risk. Diagnosis is usually conf irmed by detection of stained organisms; however, staining procedures vary in sensitivity and ease of use. Robust polymerase chain reaction (PCR) prot ocols with good predictive results may be useful in the future. Therapy fal ls into two categories: for acute primary infections and for prophylaxis. A confirmed diagnosis ensures that patients do not receive potentially toxic medication (adverse drug reactions can occur). Prophylaxis can dramaticall y reduce the frequency of PCP in HIV patients, and its more widespread use should lead to a decline in the incidence of PCP in the future.