Pneumocystis jirovecii pneumonia is a serious opportunistic infection in immunocompromised individuals. Despite recognized person-to-person transmission and healthcare-associated outbreaks, optimal infection control strategies remain unclear. The COVID-19 pandemic led to the implementation of universal masking and physical distancing in hospitals, providing a unique setting to observe P. jirovecii transmission under stringent “droplet precaution”-like conditions. This study investigated healthcare-associated P. jirovecii transmission between June 2020 and November 2021.

Retrospective cohort study.

One tertiary-care hospital in Montréal, QC, Canada.

All patients with P. jirovecii pneumonia at our institution during that period.

Cases were identified via laboratory data and chart review. P. jirovecii-positive samples underwent genotyping using multilocus sequence typing. A transmission map was constructed based on shared genotypes and spatiotemporal overlap of hospital visits within a defined window of potential exposure.

Twenty-eight P. jirovecii pneumonia cases were identified. Genotyping succeeded at providing a distinct sequence type (ST) in 21 cases, revealing 7 patients with shared genotypes (3 with ST52, 2 with STX7, 2 with ST19). The transmission map of 12 patients with shared or unknown genotypes revealed 34 same-day and 34 within-one-day contacts, exclusively within outpatient clinics and imaging facilities. Three spatiotemporal clusters of plausible healthcare-associated transmission were identified despite universal masking.

The occurrence of plausible healthcare-associated P. jirovecii transmission despite stringent universal masking suggests that traditional “droplet precautions” alone may be insufficient to prevent spread, supporting airborne transmission. Infection prevention strategies may need to be expanded in high-risk settings and should account for airborne transmission.