Article summary: Association between nursing home crowding and COVID-19 infection and mortality in Ontario, Canada

Brown KA, Jones A, Daneman N, Chan AK, Schwartz KL, Garber GE, Costa AP and Stall NM. Association Between Nursing Home Crowding and COVID-19 Infection and Mortality in Ontario, Canada. JAMA Intern Med. Published online November 09, 2020. doi:10.1001/jamainternmed.2020.6466

This article investigates the association between “crowding” in nursing homes (measured as sharing rooms and bathrooms) and COVID-19 cases and mortality in the first months of the COVID-19 pandemic, this summary aims to provide a non-technical summary, for full details of the methods and findings, please check the original publication.

Methods and data:

The data is from a cohort of over 78,000 residents in over 600 nursing homes in Ontario (Canada), during 52 days, from the 29th March (the date of the first reported outbreak in a nursing home in Ontario) to the 20th May.

The authors used the mean number of residents per bedroom and bathroom across an entire nursing home as an “index of crowding”. Nursing home rooms in Ontario range from single rooms with their own bathroom, single rooms with shared bathroom, double occupancy rooms and quadruple occupancy rooms.

In the study COVID-19 “cases” were defined as people living in nursing homes (residents) with a laboratory confirmation of SARS-CoV-2 infection. The outcome variables considered were the cumulative incidence (total number of cases up to the end of the period studied) per 100 nursing home residents, and number of COVID-associated deaths per 100 residents. Because crowding may only affect transmission within the home, not the risk of the infection entering the home, the authors examined “COVID-19 introduction”, that is having one more confirmed resident cases.

The authors also included other variables that may affect infection spread and mortality:

  • 5 other care home characteristics: type of ownership (private for-profit, private non-profit or municipal), size of the facility, ration of full time equivalent staff to beds, proportion of 1-bed, 2-bed, and 4-bed rooms, and design standard (to distinguish homes built before design standards were adopted in 1999).
  • Region characteristics: incidence of COVID-19 in the surrounding public health region (excluding nursing home infections) and proportion of the population born outside of Canada.
  • Resident characteristics (obtained from the Resident Assessment Instrument Minimum Data): sex, age, comorbidities (including dementia), functional dependency and educational attainment.


  • Across Ontario, of the 78,607 people living in nursing homes, 36.9% of them were in single bed rooms, 37.3% in double rooms and 25.8% in quadruple rooms. Half of the 618 nursing homes for which data were available, were built before new standards adopted in 1999 (which allowed for quadruple rooms). 69.8% of residents had dementia.
  • Of 78.607 residents, 5,218 (6.6%) had confirmed COVID-19 infections and 1,452 (1.8%) died. 4,496 infections occurred in just 63 homes (10% of all homes).
  • Nursing homes with higher levels of crowding (measured using the index developed by the authors) had significantly higher incidence of COVID-19 infections (9.7%), compared to less crowded nursing homes (4.5%). Mortality was also significantly lower in nursing homes with lower crowding (2.7% compared to 1.3%. The probability of having a single infection did not differ by level of crowding.
  • The authors simulated the impact of reducing crowding and estimated that: if all 4-bed rooms in Ontario had been converted to 2-bed rooms, there would have been 998 (19.1%) fewer infections and 263 fewer deaths (18.1%). If all multiple occupancy rooms had been converted to single occupancy, there would have been 1,641 (31.4%) fewer infections and 437 fewer (30.1%). This would have required an additional 29,871 rooms.


The authors note a number of limitations to their study. An important one to note is that some of the explanatory factors, such as crowding and whether the homes were built before the 1999 standards were strongly linked. They highlight that some of the design standards adopted in 1999 (such as larger room sizes, improved ventilation and smaller self-contained units) may have also played a role in reducing transmission and facilitating the implementation of cohorting measures.

Policy implications:

  • The authors suggest that cohorting policies to reduce the spread of COVID-19 and mortality within a nursing home may be ineffective in crowded homes with many shared rooms. (‘Cohorting’ is when those individuals who may be infected and those unlikely to be infected are cared for in separate parts of a care facility and by different groups of staff).
  • They propose adopting measures such as adapting hotels and other facilities as temporary nursing homes and carrying out rapid structural adaptations to existing homes.

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