Sporadic SARS-CoV-2 cases at the neighbourhood level in Toronto, Ontario, 2020: a spatial analysis of the early pandemic period.

Background: As the largest city in Canada, Toronto has played an important role in the dynamics of SARS-CoV-2 transmission in Ontario, and the burden of disease across Toronto neighbourhoods has shown considerable heterogeneity. The purpose of this study was to investigate the spatial variation of sporadic SARS-CoV-2 cases in Toronto neighbourhoods by detecting clusters of increased risk and investigating effects of neighbourhood-level risk factors on rates.
Methods: Data on sporadic SARS-CoV-2 cases, at the neighbourhood level, for Jan. 25 to Nov. 26, 2020, were obtained from the City of Toronto COVID-19 dashboard. We used a flexibly shaped spatial scan to detect clusters of increased risk of sporadic COVID-19. We then used a generalized linear geostatistical model to investigate whether average household size, population density, dependency ratio and prevalence of low-income households were associated with sporadic SARS-CoV-2 rates.
Results: We identified 3 clusters of elevated risk of SARS-CoV-2 infection, with standardized morbidity ratios ranging from 1.59 to 2.43. The generalized linear geostatistical model found that average household size (relative risk [RR] 2.17, 95% confidence interval [CI] 1.80-2.61) and percentage of low-income households (RR 1.03, 95% CI 1.02-1.04) were significant predictors of sporadic SARS-CoV-2 cases at the neighbourhood level.
Interpretation: During the study period, 3 clusters of increased risk of sporadic SARS-CoV-2 infection were identified, and average household size and percentage of low-income households were found to be associated with sporadic SARS-CoV-2 rates at the neighbourhood level. The findings of this study can be used to target resources and create policy to address inequities that are shown through heterogeneity of SARS-CoV-2 cases at the neighbourhood level in Toronto, Ontario.
Competing Interests: Competing interests: Lindsay Obress reports student stipend support from the OVC Scholarships & Fellowships Program. David Fisman reports 2019 COVID-19 Rapid Research Funding (OV4-170360); payment or honoraria for serving on advisory boards for Pfizer, Seqirus, Sanofi and AstraZeneca vaccines; and payment for serving as a legal expert for the Ontario Nurses Association and Elementary Teachers’ Federation of Ontario. Amy Greer reports research funding from the Canada Research Chairs Program, COVID-19 research funding from the University of Guelph and the Public Health Agency of Canada (PHAC), consulting fees from the Ontario Secondary School Teachers’ Federation for serving as a scientific advisor related to epidemiology of COVID-19 in Ontario, unpaid work as an advisory board member on pandemic responsive design for Fabrik Architects Inc., unpaid work as a coauthor on “School Operation for the 2021–2022 Academic Year in the Context of the COVID-19 Pandemic” for the Ontario COVID-19 Science Advisory Table, unpaid work as an advisory board member for the National Collaborating Centre for Infectious Diseases, and unpaid work as a member of the PHAC Modelling Expert Advisory Group. No other competing interests were declared.
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