Household transmission of COVID19 in Costa Rica

National Institute Of Allergy And Infectious Diseases

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Abstract

Background Prior research has shown variability in household secondary attack rates (SAR) and transmission risks of SARS-CoV-2, which remains poorly understood. To address these questions, we conducted a household serologic study nested within a larger prospective cohort study of SARS-CoV-2 in Costa Rica. Methods Household contacts of SARS-CoV-2 positive index cases were enrolled. Demographic, clinical, and behavioral information was collected from cases and their household contacts. Blood specimens were collected from contacts within 30-60 days of index case diagnosis and serum was tested for presence of spike and nucleocapsid SARS-CoV-2 IgG antibodies. SARS-CoV-2 infection among contacts was defined based on the presence of both spike and nucleocapsid antibodies. A chain binomial model was fitted to jointly estimate household and community risk of infection and assess transmission heterogeneities. Findings Overall, 719 household contacts of 304 household index cases were enrolled from November 21, 2020, through July 31, 2021. The estimated household secondary attack rate was 32% and the average community infection risk was 19%. Not sharing a bedroom with the index case reduced the risk of household transmission by 71% (OR= 0.29 with 95%CI:0.13-0.53), and mask wearing by the index case reduced the risk by 62% (OR= 0.38 with 95%CI: 0.12-0.83). The estimated distribution of household SAR was highly heterogeneous across index cases, with 36% of index cases responsible for 80% of secondary cases. This heterogeneity was partially explained by adoption of prevention measures within the household Interpretation We have identified practical and effective non-pharmaceutical prevention measures, which account for a major source of transmission heterogeneity within the household.