Healthcare-associated <i>Pneumocystis jirovecii</i> transmission in the era of universal masking and distancing

OBJECTIVE: transmission between June 2020 and November 2021. DESIGN: Retrospective cohort study. SETTING: One tertiary-care hospital in Montréal, QC, Canada. PATIENTS: pneumonia at our institution during that period. METHODS: -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. RESULTS: 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. CONCLUSION: 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.