Natural history of asymptomatic and symptomatic pneumocystis carinii infection in HIV infected patients.

The natural appearance of Pneumocystis carinii in induced sputum samples was studied in 60 HIV-infected patients with severe immunodeficiency and without a history of P. carinii pneumonia (PCP). The patients were prospectively evaluated for occurrence of P. carinii in induced sputum samples, PCP diagnosis and CD4+ cell counts during observation periods of 2 to 31 months. P. carinii was detected in 16 patients all of whom developed clinical PCP. In 5 patients P. carinii was detected 3 weeks to 8 months prior to clinical symptoms. Immunofluorescence using monoclonal antibody 3F6 was more sensitive than toluidine in detecting P. carinii in sputum samples (p < 0.05). In the patients who developed PCP a drop of the mean CD4 count to 40-50 x 10(6)/l was observed 200 days before diagnosis. However, out of 13 patients with CD4 counts of 0-20 x 10(6)/l only 7 developed PCP during 200 days of observation. The results do not support the suggested reactivation of a latent infection present in the vast majority of adults. PCP may instead result from exposure to the organism or presence of an unknown cofactor. We conclude that P. carinii is present in some asymptomatic HIV patients and that the detection of the organism in sputum should be regarded as pathological and prophylaxis or treatment inserted. The risk of transmission of P. carinii to patients with severe immunodeficiency should be seriously considered.