Household transmission of SARS-CoV-2: a prospective observational study in Bosnia and Herzegovina, August - December 2020

Abstract Background We estimated the secondary attack rate (SAR) of SARS-CoV-2 and identified risk factors for infection among members of households with a COVID-19 index case to inform preventive measures. Methods Between 3 August and 19 December 2020, we implemented a household transmission study based on a standardized WHO protocol. We recruited laboratory-confirmed SARS-CoV-2 infected cases through the federal COVID-19 database. Trained contact-tracers interviewed index cases and household members to collect information on demographic, clinical, and behavioral factors. Contacts were followed up for 28 days to identify secondary infections. We estimated SAR and computed odds ratios for risk factors for transmission. Results We included 383 households and 793 contacts. The overall SAR was 17% (95% CI: 14–21). Contacts had an increased odds of infection if the primary case had a cough and runny nose (OR: 4.31 [95% CI: 1.60–11.63]), and if the contact was aged 18–49 years, kissed the primary case or shared a meal with the primary case, OR: 4.67 (95% CI: 1.83–11.93), OR: 3.16 (95% CI 1.19–8.43) and OR: 3.10 (95% CI 1.17–8.27), respectively. Conclusions Our results add to the global literature by providing evidence from a middle income setting. Standard preventive measures in households with positive cases remain critical to reduce transmission.