A New PCR-Based Assay for Testing Bronchoalveolar Lavage Fluid Samples from Patients with Suspected Pneumocystis jirovecii Pneumonia.

To support the clinical laboratory diagnosis of Pneumocystis jirovecii ( PJ ) pneumonia (PCP), an invasive fungal infection mainly occurring in HIV-negative patients, in-house or commercial PJ -specific real-time quantitative PCR (qPCR) assays are todays' reliable options. The performance of these assays depends on the type of PJ gene (multi-copy mitochondrial versus single-copy nuclear) targeted by the assay. We described the development of a PJ -PCR assay targeting the dihydrofolate reductase (DHFR)-encoding gene. After delineating its analytical performance, the PJ -PCR assay was used to test bronchoalveolar lavage (BAL) fluid samples from 200 patients (only seven were HIV positive) with suspected PCP. Of 211 BAL fluid samples, 18 (8.5%) were positive and 193 (91.5%) were negative by PJ -PCR. Of 18 PJ -PCR-positive samples, 11 (61.1%) tested positive and seven (38.9%) tested negative with the immunofluorescence assay (IFA). All (100%) of the 193 PJ -PCR-negative samples were IFA negative. Based on IFA/PCR results, patients were, respectively, classified as having ( n = 18) and not having ( n = 182) proven ( PJ -PCR+/IFA+) or probable ( PJ -PCR+/IFA-) PCP. For 182 patients without PCP, alternative infectious or non-infectious etiologies were identified. Our PJ -PCR assay was at least equivalent to IFA, fostering studies aimed at defining a qPCR-based standard for PCP diagnosis in the future.