Oxygenation-Based Severity Stratification and a Proposed Clinical Diagnostic Workflow for Non-HIV Pneumocystis jirovecii Pneumonia: A Single-Center Observational Study

Non-HIV Pneumocystis jirovecii pneumonia (PJP) is a life-threatening opportunistic fungal pneumonia that may progress rapidly in immunocompromised hosts. Broad bronchoalveolar lavage fluid (BALF) molecular testing supports microbiologic recognition, but additional organisms often require bedside adjudication. We conducted a single-center observational study of 49 HIV-negative adults with clinically confirmed PJP, routine BALF metagenomic next-generation sequencing support, and complete 30-day follow-up. Diagnosis required compatible symptoms and chest computed tomography findings, microbiologic support for P. jirovecii, and infectious disease specialist exclusion of isolated colonization. The primary endpoint was ICU-level care requirement, defined as ICU admission, invasive mechanical ventilation, or 30-day all-cause mortality. Recent immunosuppressive exposure was present in 48 patients (98.0%). ICU-level care was required in 15 patients (30.6%); all ventilation and death events occurred in this group, and 30-day mortality was 10.2%. Baseline PaO2/FiO2 < 200 mmHg was associated with higher proportions of ICU admission, mechanical ventilation, and death. Chronic kidney disease, lower creatinine clearance, higher lactate dehydrogenase, and bacterial co-pathogen context showed exploratory signals, whereas overall co-pathogen positivity was heterogeneous. These findings support integrating oxygenation status, host vulnerability, and conservative co-pathogen adjudication to guide escalation and antimicrobial decisions after BALF testing.