An Outbreak of Multidrug-Resistant Shigella flexneri Serotype 2a Among People Experiencing Homelessness in Vancouver

Background: We describe a community-based outbreak of multidrug-resistant Shigella flexneri serotype 2a among people experiencing homelessness (PEH) in Vancouver’s Downtown Eastside during the COVID-19 pandemic. Methods: In this observational cohort study, we followed the Outbreak Reports and Intervention Studies of Nosocomial Infection (ORION) reporting guidelines. We identified cases by laboratory surveillance and collected demographic and clinical data from the medical charts or patient interviews. We implemented enhanced surveillance and disseminated testing and management guidelines. Shigella flexneri isolates were serotyped, and whole-genome sequencing was performed. Results: We identified 101 confirmed cases of Shigella flexneri 2a (80% male; median age 43) between 31 January and 16 December 2021. All the affected individuals experienced homelessness, and substance use disorder was the most common comorbidity (88%). Five patients required ICU hospitalization, and one death occurred within 30 days. Core-genome multilocus sequence typing analysis confirmed a clonal outbreak. All S. flexneri isolates were phenotypically and genotypically multidrug-resistant. Conclusions: COVID-19 exacerbated longstanding public health concerns around the dearth of hygiene and sanitation resources available to PEH. Preventing similar outbreaks will require addressing these risks and finding solutions to the crisis of homelessness in Canada.