Quantifying Contact Patterns in Response to COVID-19 Public Health Measures in Canada

Brankston, G.; Merkley, E.; Fisman, D. N.; Tuite, A. R.; Poljak, Z.; Loewen, P. J.; Greer, A. L.

Background: A variety of public health measures have been implemented during the COVID-19 pandemic in Canada to reduce contact between individuals. Objective: The objective of this study was to construct contact patterns to evaluate the degree to which social contacts rebounded to normal levels, as well as direct public health efforts toward age- and location-specific settings. Design: Four population-based cross-sectional surveys. Setting: Canada. Participants: Members of a paid panel representative of Canadian adults by age, gender, official language, and region of residence. Methods: Respondents provided information about the age and setting for each direct contact made in a 24-hour period. Contact matrices were constructed and contacts for those under the age of 18 years imputed. The next generation matrix approach was used to estimate the reproduction number (Rt) for each survey. Respondents with children estimated the number of contacts their children made in school and extracurricular settings. Results: Estimated Rt values were 0.49 (95% CI: 0.29-0.69) for May, 0.48 (95% CI: 0.29-0.68) for July, 1.06 (95% CI: 0.63-1.52) for September, and 0.81 (0.47-1.17) for December. The highest proportion of reported contacts occurred within the home (51.3% in May), in other locations (49.2% in July) and at work (66.3% and 65.4% in September and December). Respondents with children reported an average of 22.7 (95% CI: 21.1-24.3) (September) and 19.0 (95% CI 17.7-20.4) (December) contacts at school per day per child in attendance. Conclusion: The skewed distribution of reported contacts toward workplace settings in September and December combined with the number of reported school-related contacts suggest that these settings represent important opportunities for transmission emphasizing the need to ensure infection control procedures in both workplaces and schools.