Pneumocystis jirovecii Pneumonia Diagnosis with Oropharyngeal Wash PCR in Immunocompromised Patients—A Systematic Review

Background/Objectives:  Pneumocystis jirovecii pneumonia (PJP) remains a major cause of morbidity and mortality in immunocompromised patients. Bronchoalveolar lavage (BAL) is the diagnostic gold standard but is invasive and often impractical in critically ill patients. Oropharyngeal wash (OW) polymerase chain reaction (PCR) offers a rapid, non-invasive alternative. We performed a systematic review focusing on this respiratory sample’s diagnostic accuracy and clinical utility. Methods: We searched PubMed, Scopus, Web of Science, Cochrane Library, and clinical trial registries including ClinicalTrials.gov and MedRxiv for studies of PCR-based P. jirovecii detection in OW samples from immunocompromised adults, using BAL or induced sputum as reference standards. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology was followed. Quality was assessed with Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2), and pooled sensitivity/specificity were estimated using a bivariate random-effects model. Results: Twelve studies (n = 633; 346 confirmed PJP cases) met the inclusion criteria. Most cohorts were human immunodeficiency virus (HIV)-positive. Pooled sensitivity was 68.3% (95% CI: 59.2–75.9) and specificity 91.8% (95% CI: 85.9–95.3); the area under the summary receiver operating characteristic curve (AUC) was 0.887. Diagnostic yield improved with pre-sample cough induction, 60-s gargling, early sampling before extended therapy, and higher fungal loads. Risk of bias was low, and no significant publication bias was detected. Conclusions: OW-based PCR delivers high specificity and moderate sensitivity for PJP diagnosis, offering a safe, scalable, and patient-friendly alternative when invasive testing is unfeasible. Optimizing collection protocols and expanding evaluation to non-HIV immunosuppressed populations could enhance its role as an early screening tool, enabling faster treatment decisions and reducing unnecessary antimicrobial exposure.