A Prospective Study on the Transmission Dynamics of Corona Virus Disease (2019) (COVID-19) Among Household Contacts in Delhi, India

Background: Close settings such as households having fixed populations provide opportunities for tracking the viral transmission patterns of emerging respiratory infections. This study was conducted to gain an understanding of the transmission dynamics of COVID-19 among the household contacts of laboratory-confirmed cases of COVID-19, as well as to have an insight into the information on key clinical, epidemiological and virological characteristics of COVID-9 infection. Materials and Methods: This was a prospective case ascertained study conducted among the household contacts of laboratory-confirmed COVID-19 cases residing in the Central and North East districts of Delhi between December 28, 2020 and June 28,2021. The ‘household contact’ was defined as any person who has resided in the same household as a confirmed COVID-19 primary case. Baseline data collection and sample collection for RT PCR and serology from the primary case and the contacts were done on day one of visit and then they were followed up on days 7, 14 and 28 for development of symptoms, antigen testing from nasopharyngeal samples and blood specimen for antibody presence. Also, a daily symptom diary was maintained for all the primary cases and contacts for 28 days from enrolment both by the study participants and the project field investigators. Results: A total of 109 primary cases and their 202 household contacts were included in the study analysis. The secondary attack rate (SAR) estimated was 13.86% (9.71%,19.39%) and the secondary infection rate was 33.16% (26.97%, 40.00%). The serial interval and basic reproduction number(R0) within household were estimated to be 3.6± 5.73 days and 1.26.[95% C.I. 1.21-1.31] respectively. The proportion of secondary cases being symptomatic and asymptomatic was 24 (34.78%) and 45 (65.22%) respectively. On univariate analysis, the significant predictors/risk factors of the infection were location of household in Central district (SAR= 20% [13.75,28.16]) vs North East District (SAR= 4.87% [1.83-12.35]) p= 0.002, sharing of utensils (SAR= 42.85% [14.26-77.11], p=0.02), and using the room to sleep where case has been isolated (SAR= 25% [12.97-42.71], p=0.047). Other socio-demographic factors like sex, sharing of toilet, presence of comorbidity was not significantly associated. It was also observed that only one in 89 cases needed hospitalisation among the total cases in household (1.1%) in both the districts. Conclusion: The transmission dynamics was observed to be higher among the household contacts. Therefore, it is needed that the primary case and their contacts maintain COVID-19 appropriate behaviour within the household to interrupt the transmission of infection. Strengthening of testing capacity and early identification of primary case through active and passive surveillance will help to break the transmission chain at household level as well as prevent the spread in community.