Association between use of a voluntary isolation centre and reduced household SARS-CoV-2 transmission: A matched cohort study from Toronto, Canada

Background Throughout the COVID-19 pandemic, many jurisdictions established isolation centres to help reduce household transmission; however, few real-world studies support their effectiveness. We compared the risk of transmission among households where first cases used the Toronto Voluntary Isolation Centre (TVIC) compared to households receiving routine self-isolation guidance, prior to widespread vaccine availability. Methods Households with a first case having symptom onset between September 2020, and March 2021, 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. Results 303 TVIC households were matched with 2,943 self-isolation households. Median duration from first case symptom onset to TVIC check-in was 3 days (IDR [interdecile range]=1-6 days); median check-out date was 11 days after onset (IDR=10-13 days). The attack rate among TVIC households was 5.2% (53/1,015) compared to 8.4% (787/9,408) among self-isolation households (hazard ratio [HR]=0.50, 95% confidence interval [CI]=0.28-0.90). Greater reductions were observed when first cases isolated sooner after symptom onset (HR=0.37, 95%CI: 0.13-1.04), and in larger (HR=0.30, 95%CI: 0.14-0.67) and more crowded (HR=0.34, 95%CI: 0.15-0.77) households. Conclusions Use of a voluntary isolation centre was associated with a 50% reduction in household SARS-CoV-2 attack rate, prior to the availability of vaccines. Beyond SARS-CoV-2, voluntary isolation centres may help control resurgences of other communicable infections, or future pandemic pathogens, in particular for individuals experiencing difficulties isolating.