To illustrate the extent of transmission, identify affecting risk factors and estimate epidemiological modeling parameters of SARS-CoV-2 in household setting.

We enrolled 35 confirmed index cases and their 148 household contacts, January 2020–February 2020, in Zhuhai, China. All participants were interviewed and asked to complete questionnaires. Household contacts were then prospectively followed active symptom monitoring through the 21-day period and nasopharyngeal and/or oropharyngeal swabs were collected at 3-7 days intervals. Epidemiological, demographic and clinical data (when available) were collected.

Assuming that all these secondary cases were infected by their index cases, the second infection rate (SIR) in household context is 32.4% (95% confidence interval [CI] 22.4%-44.4%), with 10.4% of secondary cases being asymptomatic. Multivariate analysis showed that household contacts with underlying medical conditions, a history of direct exposure to Wuhan and its surrounding areas, and shared vehicle with an index patient were associated with higher susceptibility. Household members without protective measures after illness onset of the index patient seem to increase the risk for SARS-CoV-2 infection. The median incubation period and serial interval within household were estimated to be 4.3 days (95% CI; 3.4 to 5.3 days) and 5.1 days (95% CI; 4.3 to 6.2 days), respectively.

Early isolation of patients with COVID-19 and prioritizing rapid contact investigation, followed by active symptom monitoring and periodic laboratory evaluation, should be initiated immediately after confirming patients to address the underlying determinants driving the continuing pandemic.