Evaluation of diagnostic value and epidemiological implications of PCR forPneumocystis carinii in different immunosuppressed and immunocompetent patient groups

To evaluate the value of single and nested PCRs for diagnosis of Pneumocyst is carinii pneumonia (PCP) in a variety of respiratorily distressed patient groups, 574 respiratory samples from 334 patients (89 human immunodeficien cy virus [HIV]-positive patients, 61 transplant recipients, 66 malignancy p atients, 34 otherwise immunosuppressed patients, and 84 immunocompetent pat ients) were prospectively examined by microscopy and single and nested PCRs , The resulting data were correlated with clinical evidence of PCP, Microsc opy and single PCR of bronchoalveolar lavage (BAL) specimens from HIV patie nts were 100% sensitive and specific in detecting PCP, whereas nested PCR, although being 100% sensitive, reached a specificity of only 97.5%. In the three non-HIV immunosuppressed patient groups, both single and nested PCR i nvariably produced lower positive predictive values than microscopy. Among immunocompetent patients, the positive predictive values of both PCRs mere 0%. Therefore, the diagnostic values of the PCR methods tested do not seem to offer any additional advantage compared to that of conventional microsco py for these patient groups, However, nested PCR identified a significant p ercentage of clinically silent P. carinii colonizations in about 17 to 20% of immunocompetent and immunosuppressed non-HIV patients.