Molecular diagnosis of Pneumocystis jiroveci pneumonia in immunocompromised patients.

Pneumocystis jiroveci is the major cause of pneumonia in immunocompromised patients. To evaluate the performance of single and nested-polymerase chain reaction (PCR) methods compared with immunofluorescent assay (IFA) and cytological staining for diagnosis of P. jiroveci infection, the bronchoalveolar lavage (BAL) and sputum samples from 60 immunocompromised patients were studied. Between January 2005 and March 2008, 75 respiratory specimens (41 BAL and 34 sputum samples) were examined for P. jiroveci identification. We used the clinical classification as our diagnostic standard and we considered true positive the definite or probable Pneumocystis pneumonia. Fourteen patients (23.3%) developed Pneumocystis pneumonia. Eleven patients had a positive IFA but only nine were positive by cytological staining. Sixteen patients had a positive detection of P. jiroveci by PCR and nested-PCR. Thirteen of these patients were considered as having a definite Pneumocystis pneumonia and one patient with a probable Pneumocystis pneumonia. Five other patients had a positive detection only by nested-PCR. These patients were classified as no Pneumocystis pneumonia. PCR detection of P. jiroveci is a very sensitive test and will offer a powerful technique in clinical laboratories for the routine diagnosis of Pneumocystis pneumonia. Using the nested-PCR, additional clinical cases can be diagnosed, but there is then an obvious risk of detecting subclinical colonisation by P. jiroveci.