The role of case importation in explaining differences in early SARS-CoV-2 transmission dynamics in Canada-A mathematical modeling study of surveillance data

Arnaud Godin; Yiqing Xia; David L Buckeridge; Sharmistha Mishra; Dirk Douwes-Schultz; Yannan Shen; Maxime Lavigne; Mélanie Drolet; Alexandra M Schmidt; Marc Brisson; Mathieu Maheu-Giroux

doi:10.1016/j.ijid.2020.10.046

The role of case importation in explaining differences in early SARS-CoV-2 transmission dynamics in Canada-A mathematical modeling study of surveillance data

Int J Infect Dis. 2021 Jan:102:254-259. doi: 10.1016/j.ijid.2020.10.046. Epub 2020 Oct 25.

Authors

Affiliations

¹ Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: arnaud.godin@mail.mcgil.ca.
² Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: yiqing.xia@mail.mcgill.ca.
³ Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: david.buckeridge@mcgill.ca.
⁴ Li Ka Shing Knowledge Institute, St. Michael's Hospital, Unity Health Toronto, Department of Medicine, Toronto, Ontario, Canada; St. Michael's Hospital, University of Toronto, Institute of Health Policy, Management and Evaluation, Toronto, Ontario, Canada. Electronic address: sharmistha.mishra@utoronto.ca.
⁵ Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: dirk.douwes-schultz@mail.mcgill.ca.
⁶ Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: yannan.shen@mail.mcgill.ca.
⁷ Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: maxime.lavigne@mail.mcgill.ca.
⁸ Centre de Recherche du CHU de Quebec and Département de Médecine Sociale et Préventive, Université Laval, Ville de Quebec, Quebec, Canada. Electronic address: Melanie.Drolet@crchudequebec.ulaval.ca.
⁹ Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: alexandra.schmidt@mcgill.ca.
¹⁰ Centre de Recherche du CHU de Quebec and Département de Médecine Sociale et Préventive, Université Laval, Ville de Quebec, Quebec, Canada. Electronic address: marc.brisson@crchudequebec.ulaval.ca.
¹¹ Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health, McGill University, Montréal, Quebec, Canada. Electronic address: mathieu.maheu-giroux@mcgill.ca.

Abstract

Objective: The North American coronavirus disease-2019 (COVID-19) epidemic exhibited distinct early trajectories. In Canada, Quebec had the highest COVID-19 burden and its earlier March school break, taking place two weeks before those in other provinces, could have shaped early transmission dynamics.

Methods: We combined a semi-mechanistic model of SARS-CoV-2 transmission with detailed surveillance data from Quebec and Ontario (initially accounting for 85% of Canadian cases) to explore the impact of case importation and timing of control measures on cumulative hospitalizations.

Results: A total of 1544 and 1150 cases among returning travelers were laboratory-confirmed in Quebec and Ontario, respectively (symptoms onset ≤03-25-2020). Hospitalizations could have been reduced by 55% (95% CrI: 51%-59%) if no cases had been imported after Quebec's March break. However, if Quebec had experienced Ontario's number of introductions, hospitalizations would have only been reduced by 12% (95% CrI: 8%-16%). Early public health measures mitigated the epidemic spread as a one-week delay could have resulted in twice as many hospitalizations (95% CrI: 1.7-2.1).

Conclusion: Beyond introductions, factors such as public health preparedness, responses and capacity could play a role in explaining interprovincial differences. In a context where regions are considering lifting travel restrictions, coordinated strategies and proactive measures are to be considered.

Keywords: Case introductions; Epidemiology; Infectious diseases; Public health; Travel.

MeSH terms

Adult
Aged
COVID-19 / epidemiology
COVID-19 / transmission*
Canada / epidemiology
Humans
Middle Aged
Models, Theoretical
Public Health
SARS-CoV-2*
Travel*