Transmissibility of severe acute respiratory syndrome coronavirus 2 among household contacts of coronavirus disease 2019‐positive patients: A community‐based study in India

BACKGROUND: This study identified the risk factors for severe acute respiratory syndrome coronavirus 2 infection among household contacts of index patients and determined the incubation period (IP), serial interval, and estimates of secondary infection rate in Kerala, India. METHODS: We conducted a cohort study in three districts of Kerala among the inhabitants of households of reverse transcriptase polymerase chain reaction‐positive coronavirus disease 2019 patients between January and July 2021. About 147 index patients and 362 household contacts were followed up for 28 days to determine reverse transcriptase polymerase chain reaction positivity and the presence of total antibodies against SARS‐CoV‐2 on days 1, 7, 14, and 28. RESULTS: The mean IP, serial interval, and generation time were 1.6, 3, and 3.9 days, respectively. The secondary infection rate at 14 days was 43.0%. According to multivariable regression analysis persons who worked outside the home were protected (adjusted odds ratio [aOR], 0.45; 95% confidence interval [CI], 0.24–0.85), whereas those who had kissed the coronavirus disease 2019‐positive patients during illness were more than twice at risk of infection (aOR, 2.23; 95% CI, 1.01–5.2) than those who had not kissed the patients. Sharing a toilet with the index patient increased the risk by more than twice (aOR, 2.5; 95% CI, 1.42–4.64) than not sharing a toilet. However, the contacts who reported using masks (aOR, 2.5; 95% CI, 1.4–4.4) were at a higher risk of infection in household settings. CONCLUSIONS: Household settings have a high secondary infection rate and the changing transmissibility dynamics such as IP, serial interval should be considered in the prevention and control of SARS‐CoV‐2.