An Observational Analysis of a Large Cohort of

Background: Methods: A retrospective review was conducted of adult patients who met criteria for proven or probable PCP from 2017 to 2024 across a large academic multicenter health system. The primary outcome was mortality among cohorts, defined by etiology of immunosuppression through univariate and age-adjusted logistic regression. Secondary analyses included trends in annual diagnoses and testing patterns. Results: A total of 701 patients met criteria for inclusion, representing one of the largest clinically characterized cohorts of PCP to date. The median age was 65 years (IQR, 54-73) and 62% were male. The most common risk groups were hematologic malignancy (32.2%), solid tumor cancers receiving chemotherapy (22.4%), and autoimmune disease with immunosuppression (17.7%). Annual PCP diagnoses increased at a rate of 15.8% (95% CI, 8.9%-23.2%) in parallel with increased testing. Only 5.4% of patients were receiving prophylaxis at the time of diagnosis. Overall mortality was 20% (95% CI, 17%-23%) and highest in cirrhosis (adjusted odds ratio, 6.24; 95% CI, 2.84-13.69; Conclusions: PCP in the current era affects a broad range of patients who are immunocompromised, with high associated mortality and low rates of prophylaxis. Patients with solid tumors and those with cirrhosis are at particularly high risk of mortality. These findings highlight the need to reassess and redefine PCP prophylaxis guidelines in specific populations and our understanding of who is at risk.