Dynamics of transmission of COVID-19 cases and household contacts: A prospective cohort study

Rajmohan, P.; Jose, P.; Thodi, J. B. A.; Thomas, J.; Raphael, L.; Krishna, S.; Gopinathan, U. U.; Kuttichira, P.

Objective: To study the transmission dynamics of coronavirus disease 2019 (COVID-19) among 101 confirmed cases and their 387 household contacts and to determine risk factors associated with secondary attack among the household contacts. Methods: A prospective cohort study was conducted from January 1st 2021 to February 28th 2021, among 101 SARS-CoV-2 cases and 387 household contacts who were followed up for 14 days from the last day of contact with the index case of COVID-19. The dynamics of disease transmission was estimated, and factors affecting transmission risk were analyzed. Besides, the association between various factors and household secondary attack rate was determined. Results: The median incubation period was found to be 5 days, and the observed reproductive number (R) was found to be 1.63 (95% CI: 1.28-1.98). The mean household secondary attack rate was 40.7%. Contacts with comorbidities like diabetes mellitus, hypertension, dyslipidemia, and hypothyroidism had significantly higher attack rates (P<0.05). Conclusions: As new variants of SARS-CoV-2 emerges, it is crucial to know the trasmission dynamics. This study shows a high secondary attack rate of COVID-19 among household contacts that must be closely monitored.