Pneumocystis jirovecii Pneumonia Outbreaks in Solid Organ Transplant Recipients: A Systematic Review of Epidemiology, Transmission Dynamics, and Outbreak Investigations.

Background

Although Pneumocystis jirovecii pneumonia (PJP) outbreaks continue to occur in solid organ transplantation (SOT) recipients, no systematic review has synthesized the available evidence to provide an aggregated understanding of their epidemiology and transmission.

Methods

We searched MEDLINE, Embase, Cochrane, and manual sources through May 1, 2024 for studies of PJP outbreaks in adult SOT recipients. Data on patient characteristics, immunosuppression, diagnostics, outcomes, outbreak investigations, and control measures were extracted. The primary outcome was all-cause mortality, and the secondary outcome was characterization of outbreak investigation.

Results

Twenty-nine outbreaks involving 360 SOT recipients (median age, 51.8 years [range, 22-70.5 years]; 32.6% female) were identified. Late-onset PJP (> 1 year posttransplant) occurred in 92.6% of outbreaks, which lasted a median of 365 days (range, 90-1260 days); kidney transplant recipients accounted for 77.8% of cases. Across 22 studies, the crude aggregate mortality was 19.0% (51 of 268 patients), while 27 of 64 patients (42.2%) required dialysis in six studies. Most patients were not on prophylaxis at diagnosis; breakthrough infections were rare (< 5%). Molecular typing was performed in most studies (21/28, 75%) among which single or predominant genotypes were identified in 19/20 (95%), supporting clonal transmission. Control measures included extended prophylaxis and surveillance, although their individual effectiveness could not be determined.

Conclusion

Transplant centers remain susceptible to prolonged PJP outbreaks associated with substantial mortality. Nosocomial airborne transmission is likely. Most outbreaks occurred after prophylaxis discontinuation, but optimal control measures and prophylaxis duration remain uncertain. Standardized investigations incorporating molecular epidemiology will guide outbreak control and prevention.