Reviewed by Dr. Michael Payne, MD, London Health Sciences Centre

A population-based, retrospective cohort study of licensed retirement homes (RH) in Ontario, Canada, from Mar. 1 to Dec. 18, 2020. This study examined the association between home-and community-level characteristics and the risk of outbreaks of SARS-CoV-2 infection in RH. The cohort included all 770 licensed RH in Ontario, with 56 491 residents. There were 273 (35.5%) RH with 1 or more outbreaks of SARS-CoV-2 infection, involving 1944 (3.5%) residents and 1101 staff (3.0%). Cases were distributed unevenly amongst RH, with 2487 (81.7%) resident and staff cases occurring in 77 (10%) homes. The adjusted hazard of an outbreak was positively associated with homes that had a large resident capacity, were co-located with a long-term care facility, were part of larger chains, offered many services onsite, saw increases in regional incidence of SARS-CoV-2 infection, and were located in a region with a higher community-level ethnic concentration. The association of outbreaks for RH with co-located LTC facilities as well as those with a higher number of services, suggest increased staff movement and staff-resident interactions may be a contributing factor to outbreaks in RH. Higher regional incidence of COVID-19 was associated with increased risk of outbreaks, however, sensitivity to this factor decreased in Wave 2, potentially a reflection of mandatory staff-resident surveillance testing and other local preventative measures introduced after Wave 1. 


Andrew P. Costa, et al. Risk factors for outbreaks of SARS-CoV-2 infection at retirement homes in Ontario, Canada: a population-level cohort study. CMAJ 2021 May 10;193:E672-80. doi: 10.1503/cmaj.202756