Secondary attack rate of COVID-19 in household contacts in the Winnipeg Health Region, Canada

Objectives Understanding important transmission parameters, such as secondary attack rates, can help in strategizing, prioritizing, and planning interventions to curb morbidity and mortality due to COVID-19. Early reports suggest the risk of transmission of SARS-CoV-2 (the pathogen that causes COVID-19 disease) is high among household contacts of cases. The purpose of this analysis was to determine the household transmissibility of SARS-CoV-2 in residents of the Winnipeg Health Region. Methods We extracted information on COVID-19 cases and their household contacts from the regional public health surveillance database and used this dataset to calculate secondary attack rates. Results We included 381 individuals from 102 unique households (102 primary cases and 279 household contacts). A total of 41 contacts from 25 households became secondary cases in the 14 days since last unprotected exposure to the primary case, resulting in a secondary attack rate of 14.7% (95% CI: 10.5-18.8). Conclusion Household transmission of SARS-CoV-2 has been an important contributor to the local COVID-19 epidemic.

Automated summary

Understanding the important transmission parameters of COVID-19, such as secondary attack rates, can help in planning interventions. A study in Winnipeg Health Region found a secondary attack rate of 14.7% among household contacts of COVID-19 cases.