Detection of Pneumocystis carinii in clinical samples by the polymerase chain reaction. Comparison with the methenamine silver technique

Background: A comparison of polymerase chain reaction (PCR) with methenamine silver stain was performed on clinical specimens for diagnosis of Pneumocystis carinii pneumonia in immunosuppressed patients.

Methods: 25 clinical samples (10 induced sputa, 12 transthoracic needle aspirations and 2 bronchoalveolar lavages) from 17 patients with AIDS and respiratory symptoms were studied. We performed DNA amplification by using 2 primers that amplify the mitochondrial large rDNA sequence of P. carinii.

Results: The sensitivity and specificity of the PCR technique were 92.8% and 100% respectively, with a positive predictive value of 100% and negative predictive value of 92.3%. The sensitivity of the silver stain were 65%, specificity 100%, positive predictive value 100% and negative predictive value 63%.

Conclusions: The PCR technique is more sensitive than the methenamine silver stain for detecting Pneumocystis carinii in respiratory specimens from patients with pneumonia. Consequently it could be a very good alternative to classical methods in diagnosis of P. carinii infections.