Household exposure to SARS-CoV-2 and association with COVID-19 severity: a Danish nationwide cohort study

Abstract

Abstract Background Households are high-risk settings for the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Severity of Coronavirus disease 2019 (COVID-19) is likely associated with the infectious dose of SARS-CoV-2 exposure. We therefore aimed to assess the association between SARS-CoV-2 exposure within households and COVID-19 severity. Methods We performed a Danish nationwide register-based cohort study including laboratory-confirmed SARS-CoV-2 infected individuals from 22 February to 6 October 2020. Household exposure to SARS-CoV-2 was defined as having one individual tested positive for SARS-CoV-2 within the household. Cox proportional-hazards models were used to estimate the association between ‘critical COVID-19’ within and between households with and without secondary cases. Results From 15,063 multi-person households, 19,773 SARS-CoV-2 positive individuals were included; 11,632 were categorized as index cases without any secondary household cases, 3,431 as index cases with secondary cases, i.e. 22.8% of multi-person households, and 4,710 as secondary cases. ‘Critical COVID-19’ occurred in 2.9 % of index cases living with no secondary cases, 4.9 % of index cases with secondary cases, and 1.3 % of secondary cases. The adjusted hazard ratio for ‘critical COVID-19’ among index cases versus secondary cases within the same household was 2.50 (95%CI=1.88-3.34), 2.27 (95%CI=1.77-2.93) for index cases in households with no secondary cases versus secondary cases, and 1.1 (95%CI=0.93-1.30) for index cases with secondary cases versus index cases without secondary cases. Conclusion We found no increased hazard ratio of ‘critical COVID-19’ among household members of infected SARS-CoV-2 index cases.