Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2024 Sep 4;24(1):2409.
doi: 10.1186/s12889-024-19853-4.

Risk factors associated with the intensity of COVID-19 outbreaks in Canadian community settings: a retrospective analysis of outbreak-level surveillance data

Demy Dam  1 , Michelle Chen  2 , Erin E Rees  3   4   5 , Bethany Cheng  2 , Lynn Sukkarieh  2 , Erin McGill  2 , Yasmina Tehami  2 , Anna Bellos  2 , Jonathan Edwin  2 , Kaitlin Patterson  2
Affiliations

Risk factors associated with the intensity of COVID-19 outbreaks in Canadian community settings: a retrospective analysis of outbreak-level surveillance data

Demy Dam et al. BMC Public Health. .

Abstract

Background: The severity of COVID-19 outbreaks is disproportionate across settings (e.g., long-term care facilities (LTCF), schools) across Canada. Few studies have examined factors associated with outbreak severity to inform prevention and response. Our study objective was to assess how outbreak severity, as measured using outbreak intensity and defined as number of outbreak-associated cases divided by outbreak duration, differed by setting and factors known to influence SARS-CoV-2 transmission.

Methods: We described outbreak intensity trends in 2021 using data from the Canadian COVID-19 Outbreak Surveillance System from seven provinces/territories, representing 93% of the Canadian population. A negative binomial fixed-effects model was used to assess for associations between the outcome, outbreak intensity, and characteristics of outbreaks: setting type, median age of cases, number at risk, and vaccination coverage of at least 1 dose. Also included were variables previously reported to influence SARS-CoV-2 transmission: stringency of non-pharmaceutical interventions (NPI) and the predominant SARS-CoV-2 variant detected by surveillance.

Results: The longest outbreaks occurred in LTCF (mean = 25.4 days) and correctional facilities (mean = 20.6 days) which also reported the largest outbreaks (mean = 29.6 cases per outbreak). Model results indicated that outbreak intensity was highest in correctional facilities. Relative to correctional facilities (referent), the second highest adjusted intensity ratio was in childcare centres (intensity ratio = 0.58 [95% CI: 0.51-0.66]), followed by LTCF (0.56 [95% CI: 0.51-0.66]). Schools had the lowest adjusted intensity ratio (0.46 [95% CI: 0.40-0.53]) despite having the highest proportion of outbreaks (37.5%). An increase in outbreak intensity was associated with increases in median age, the number at risk, and stringency of NPI. Greater vaccination coverage with at least 1 dose was associated with reduced outbreak intensity.

Conclusion: Descriptive and multivariable model results indicated that in Canada during 2021, outbreak intensity was greatest in closed congregate living facilities: correctional facilities and LTCF. Findings from this study support the importance of vaccination in reducing outbreak intensity when vaccines are effective against infection with circulating variants, which is especially important for closed congregate living facilities where NPIs are more challenging to implement.

Keywords: COVID-19; Community settings; Outbreak; Regression analysis.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Directed acyclic graph of assumptions for factors associated with outbreak intensity. Legend: The exposure is represented in a green box, conditioned variables with observed data available for this study are represented in black boxes, and the outcome is represented in a red box. Variables not in boxes were not conditioned on. PHM: public health measures
Fig. 2
Fig. 2
Temporal evolution of study variables from January to December 2021 for the seven assessed provinces/territories. Legend: (A) SARS-CoV-2 variant periods and introduction dates of the Delta and Omicron variants, (B) weekly median outbreak intensity, unweighted mean of the (C) stringency index (SI), and (D) effective reproduction number (Rt) and vaccine rollout timelines. Date labels represent week start
See this image and copyright information in PMC

Similar articles

See all similar articles

References

    1. Kain D, Stall N, Brown K, McCreight L, Rea E, Kamal M, et al. A longitudinal, clinical, and spatial epidemiologic analysis of a large COVID-19 long-term Care Home Outbreak. J Am Med Dir Assoc. 2021;22(10):2003–e20082. 10.1016/j.jamda.2021.07.021. 10.1016/j.jamda.2021.07.021 - DOI - PMC - PubMed
    1. Franco-Paredes C, Ghandnoosh N, Latif H, Krsak M, Henao-Martinez AF, Robins M, et al. Decarceration and community re-entry in the COVID-19 era. Lancet Infect Dis. 2021;21(1):e11–6. 10.1016/S1473-3099(20)30730-1. 10.1016/S1473-3099(20)30730-1 - DOI - PMC - PubMed
    1. Costa AP, Manis DR, Jones A, Stall NM, Brown KA, Boscart V, et al. Risk factors for outbreaks of SARS-CoV-2 infection at retirement homes in Ontario, Canada: a population-level cohort study. CMAJ. 2021;193(19):E672–80. 10.1503/cmaj.202756. 10.1503/cmaj.202756 - DOI - PMC - PubMed
    1. CBC News. Inside Canada’s largest COVID-19 outbreak in a federal prison. 2021. https://www.cbc.ca/news/canada/manitoba/covid-coronavirus-outbreak-priso.... Accessed 3 May 2023.
    1. CTV News. ‘Public health crisis’: Canada’s prison conditions during pandemic being investigated. 2021. https://www.ctvnews.ca/health/coronavirus/public-health-crisis-canada-s-.... Accessed 3 May 2023.

Publication types

LinkOut - more resources