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

Wilkinson, Krista; Chen, Xuan; Shaw, Souradet

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.