COVID-19 International Border Surveillance Cohort Study at Toronto's Pearson Airport

Background: Border restrictions have been a tool used to control the spread of COVID-19. Many jurisdictions have implemented quarantine and/or testing requirements for incoming travelers. Such decision-making has been largely trial and error or based on mathematical models. The primary objective was to estimate the positivity rate of air travelers coming to Toronto, Canada in in September and October, 2020, at arrival, day 7 and day 14. Secondary objectives were to estimate degree of risk based on country of origin; to assess knowledge and attitudes towards COVID-19 control measures; and subjective well-being during the quarantine period.Methods: Prospective cohort of arriving international travelers. Self-administered nasal-oral swabs were obtained on arrival, day 7, and day 14 of quarantine for RT-PCR testing for SARS-CoV2 virus and questionnaires were completed at each time point.Findings: Of 16,361 passengers enrolled, 248 (1·5%) tested positive. Of these, 167 (67%) were identified on arrival, 67 (27%) on day 7, and 14 (6%) on day 14. The positivity rate increased from 1% in September to 2% in October.Interpretation: A single arrival test will pick up two-thirds of individuals who will become positive, with most of the rest detected on the second test at day 7. These results support strategies identified through mathematical models that a reduced quarantine combined with testing can be as effective as a 14 day quarantine.Funding: Canadian Institutes of Health Research, Air Canada, and the Greater Toronto Airport Authority.Conflict of Interest: The authors have no direct financial conflicts of interest to declare. MS and DB are on the Board of Directors of McMaster Health Labs. DB is the developer of McMaster Molecular Medium.Ethical Approval: The study protocol was reviewed and approved by the Advara Research Ethics Board.