Association Between Use of a Voluntary Isolation Center and Reduced Household SARS-CoV-2 Transmission: A Matched Cohort Study From Toronto, Canada.

Abstract

Throughout the coronavirus disease 2019 (COVID-19) pandemic, many jurisdictions established isolation centers to help reduce household transmission; however, few real-world studies support their effectiveness. We compared transmission among households where first cases used the Toronto Voluntary Isolation Centre (TVIC) with households that received routine self-isolation guidance, prior to widespread vaccine availability. Households with a first severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) case that had symptom onset between September 2020 and March 2021 and that used TVIC were propensity score matched with up to 10 self-isolation households. Follow-up began for TVIC households on the day after check-in or, for matched self-isolation households, the equivalent delay since first-case symptom onset. The outcome, 28-day secondary attack rate, was analyzed using proportional hazards models. A total of 303 TVIC households were matched with 2943 self-isolation households. Median duration from first-case symptom onset to TVIC check-in was 3 days (interdecile range [IDR] = 1-6); median check-out date was 11 days after onset (IDR = 10-13). The attack rate among TVIC households was 5.2% (53/1015) compared with 8.4% (787/9408) among self-isolation households (hazard ratio [HR] = 0.50; 95% confidence interval [CI], .28-.90). Greater reductions were observed when first cases isolated sooner after symptom onset (HR = 0.37; 95% CI, .13-1.04) and in larger (HR = 0.30; 95% CI, .14-.67) and more crowded (HR = 0.34; 95% CI, .15-.77) households. Use of a voluntary isolation center was associated with a 50% reduction in household SARS-CoV-2 prior to the availability of vaccines. Beyond SARS-CoV-2, voluntary isolation centers may help control resurgences of other communicable infections or future pandemic pathogens, particularly for individuals who experience difficulties isolating.