Pneumocystis jirovecii pneumonia (PCP) is a leading cause of morbidity and mortality in HIV and other immunocompromised patients. Currently the commonly used PCR for diagnosing P. jirovecii will miss some organisms by staining methods. The authors of a study published in Clinical Microbiology and Infection  developed a new assay using the same targeted genes.

This assay was compared with the currently used PCR and other conventional assays (Giemsa staining and immunofluorescence assay).   Brochoalveolar lavage (BAL) sample collected from human immunodeficiency virus (HIV)-infected (n = 66) and non-HIV (n = 36) immunocompromised patients presenting with fever, dyspnoea, cough and pulmonary infiltrates was tested by all the assays. Pneumocystis jirovecii was diagnosed with Giemsa-stained smear, immunofluorescence assay, conventional single-round and nested PCR, and the new PCR in 46 (45.1%), 53 (52.0%), 69 (67.6%), 74 (72.6%), 87 (85.3%) and 91 (89.2%) patients, respectively.

The new PCR could detectP. jirovecii DNA in BAL fluids two to three orders of magnitude more dilute than conventional PCR.  Although both conventional and new PCR assays were highly specific for diagnosing P. jirovecii, the new PCR yielded more positive results than conventional PCR among BAL samples that were negative by both Giemsa stain and immunofluorescence assay. Hence, the new PCR offered a more sensitive detection of P. jirovecii infection and colonization than conventional PCR.