This is a summary, written by members of the CITF Secretariat, of:

Costa AP, Manis DR, Jones A, Stall NM, Brown KA, Boscard V, Castellino A, Heckman GA, Hillmer MP, Ma C, Pham P, Rais S, Sinha SK, Poss JW. Risk factors for outbreaks of SARS-CoV-2 infection at retirement homes in Ontario, Canada: a population-level cohort study. CMAJ. May 10, 2021;193(19):E672-80. doi: 10.1503/cmaj.202756

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

Dr. Andrew Costa, from McMaster University, and colleagues, have studied the risk factors for SARS-CoV-2 outbreaks at retirement homes or assisted living facilities in Ontario. In a publication in the Canadian Medical Association Journal, now also available in French, they find that the risk of a COVID-19 outbreak is higher in homes with larger resident capacity, that share space with a long-term care facility, and that offer more services onsite. The authors recommended priority vaccination for those living in homes that fit these criteria. This research was funded in part by the COVID-19 Immunity Task Force.


Key points:

  • A survey of all of the licensed retirement homes in Ontario indicated that 80% of the SARS-CoV-2 cases emerged from only 10% of the homes.
  • The size of the home, its proximity to long-term care facilities, and the local community influenced the risk of a COVID-19 outbreak.

The authors examined the association between home- and community-level characteristics and the risk of outbreaks of SARS-CoV-2 in retirement homes and assisted living facilities since the beginning of the first wave of the COVID-19 pandemic. Their cohort included all 770 licensed retirement homes in Ontario, which at the time of recruitment housed over 56,000 residents. There were 273 retirement homes (35.5%) with one or more outbreaks of SARS-CoV-2 infection, involving almost 2000 residents (3.5%) and over 1100 staff (3.0%).

The research team found that cases of SARS-CoV-2 were not distributed evenly across all retirement homes, with over 80% of the resident and staff cases occurring in only 10% of the homes. They found that the retirement homes with a higher incidence of SARS-CoV-2 infection were those with the following characteristics:

  • A larger resident capacity;
  • Co-located with a long-term care facility;
  • Part of a larger chain offering many services onsite; and
  • Located within a neighbourhood with a racialized population

Larger homes were associated with a three-fold increase in the risk of SARS-CoV-2 outbreaks. The authors propose that staff commuting to and from the home likely increased the opportunities to seed new infections. The relationship between the number of SARS-CoV-2 infections in retirement homes and in the surrounding area was stronger during Wave 1 as compared to Wave 2.

The authors showed that a subset of retirement homes in Ontario have been severely affected by the pandemic, with case fatality rates approaching those of long-term care facilities. They identified factors putting retirement homes at higher risk for SARS-CoV-2 outbreaks which can inform mitigation planning and vaccine prioritization at the provincial and regional levels, as has been done for the long-term care sector.