Polymerase chain reaction-based detection of Pneumocystis jirovecii in bronchoalveolar lavage fluid for the diagnosis of pneumocystis pneumonia.

Introduction: The diagnosis of pneumocystis pneumonia (PCP) in non-human immunodeficiency virus (HIV)-infected immunocompromised patients is notoriously difficult. The recent advent of polymerase chain reaction (PCR)-based detection systems, based on the identification of single fungal genes, has markedly improved diagnostic accuracy in this ominous disease. In an attempt to further improve diagnostic yield, the authors used a PCR-based detection system for Pneumocystis jirovecii, based on targeting 3 distinct genes.

Methods: During the 4-year period (January 2005 to January 2009), all consecutive immunocompromised patients suspected of having PCP in the differential diagnosis underwent bronchoscopy with bronchoalveolar lavage sampling for the evaluation of the etiology of pulmonary infiltrates. Bronchoalveolar fluid was tested for the presence of a wide variety of possible etiological microorganisms.

Results: In a cohort of 214 immunocompromised patients (of which 198 were non-HIV immunocompromised patients) who underwent bronchoscopy with bronchoalveolar lavage for evaluation of pulmonary infiltrates, PCR correctly diagnosed PCP in 75% (42/56) compared with 14% (8/56) diagnosed by traditional stains, and increased diagnostic yield 5.4-fold.

Conclusions: Given the absence of a sensitive gold standard, this study demonstrates the usefulness of a multigene PCR-based detection of Pneumocystis jirovecii DNA for supporting the clinical diagnosis of PCP, with high sensitivity and negative predictive value rates compared with direct stains, especially in non-HIV immunocompromised patients.