Risk factors for retirement home COVID-19 outbreaks in Ontario, Canada: A population-level cohort study

Background: Congregate living settings for older adults are hot spots for the coronavirus disease 2019 (COVID-19) pandemic in Canada and internationally. The epidemiology of COVID-19 in retirement homes (also known as assisted living facilities) is largely unknown. We examined the association between retirement home and community level characteristics and the risk of COVID-19 outbreaks in retirement homes during the first wave of the COVID-19 epidemic. Methods: We conducted a population-based retrospective cohort study of licensed retirement homes in Ontario, Canada, from March 1st - September 24th, 2020 using a COVID-19 outbreak reporting database maintained by the Ontario Retirement Homes Regulatory Authority, supplemented with data from the Ontario Ministry of Health. Our primary outcome was a COVID-19 outbreak (1 or more resident or staff confirmed case by validated nucleic acid amplification assay). We used time-dependent proportional hazards methods to model the associations between retirement home and community level characteristics and COVID-19 outbreaks. Results: Our cohort included all 770 licensed retirement homes in Ontario as of March 1st 2020, which housed 56,491 residents. There were 172 (22.3%) COVID-19 retirement home outbreaks involving 1,045 (1.9%) residents and 548 staff (1.5%). COVID-19 cases were distributed unevenly across retirement homes, with 1,593 (92.2%) resident and staff cases occurring in 77 (10%) of homes. There were 51 (6.6%) retirement homes with outbreaks resulting in one or more resident deaths, accounting for a total of 215 resident COVID-19 deaths (3.8 per 1,000 retirement home residents) and a case fatality rate of 20.5%. The adjusted hazard of a COVID-19 outbreak in a retirement home was positively associated with homes that had a large resident capacity, homes that were co-located with a long-term care facility, large corporate owned chains, homes that offered many services onsite, increases in regional COVID-19 incidence, and a higher community-level ethnic concentration. Interpretation: Readily identifiable retirement home-level characteristics are independently associated with COVID-19 outbreaks and may support risk identification. A higher ethnic concentration of the community surrounding a retirement home is associated COVID-19 outbreaks, with an uncertain mechanism.