Comparison of PCR and standard cytological staining for detection of Pneumocystis carinii from respiratory specimens from patients with or at high risk for infection by human immunodeficiency virus.

The detection of Pneumocystis carinii DNA by PCR was compared with routine cytologic staining techniques (CYT). A total of 284 clinical respiratory specimens, including 137 bronchoalveolar lavage (BAL), 63 bronchoalveolar washing, 63 sputum, and 21 induced sputum samples, obtained from patients with or at high risk for human immunodeficiency virus infection were evaluated. Eighty specimens were positive by PCR, and 69 were positive by CYT. PCR was able to detect P. carinii in more bronchoalveolar washing specimens (15 versus 11) and in comparable BAL specimens (53 versus 54) compared with CYT. PCR was particularly more sensitive than CYT in detecting P. carinii in expectorated sputum (12 versus 4 samples). Of the 19 patients whose respiratory specimens were positive for P. carinii by PCR but negative by CYT, 5 had P. carinii pneumonia (PCP) confirmed by subsequent BAL and transbronchial or mediastinal lymph node biopsy and 9 had a clinical course highly suggestive of acute PCP. Eleven (58%) of the 19 patients with discordant PCR and CYT results had received prior anti-PCP prophylaxis. In this clinical setting in particular and in the evaluation of sputum specimens, the ability of PCR to detect a low parasitic load suggests that this technique may become an important additional tool, along with current cytological methods, for the detection of P. carinii.