A Prospective Study on the Transmission dynamics of Corona virus disease (2019) (COVID-19) among Household contacts in Delhi, India.

Abstract

Background: This study was conducted to understand the transmission dynamics of COVID-19 virus among the household contacts of RT-PCR confirmed cases to have an insight on key epidemiological characteristics of the infection. Methods: This was a prospective case-ascertained study conducted among the contacts of laboratory-confirmed COVID-19 cases residing in the same household in the Central and North-East districts of Delhi between 28th December 2020, and 28th June 2021. Data and specimen for reverse transcription polymerase chain reaction (RT-PCR) and serology were collected from the primary case and their contacts on day one of the visit, and follow-up collection of data and specimen was done on day 7, 14 and 28. A daily symptom diary was also maintained for all the primary cases and their contacts till 28 days from enrolment in the study. A total of 109 houses were enrolled in the study. Results: The secondary attack rate (SAR) estimated among the household contacts was 13.86% [95% C.I. 9.71%, 19.39%] and the secondary infection rate was 33.16% [95% C.I. 26.97%, 40.00%]. The serial interval and basic reproduction number (R0) within the household were estimated to be 3.6± 5.73 days and 1.26 [95% C.I. 1.21—1.31], respectively. Significant predictors of the infection were location of household in central district (SAR = 20% [13.75, 28.16]) versus 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 a specific case has been isolated (SAR= 25% [12.97—42.71], p=0.047). Transmission from the symptomatic primary case was observed to be five times higher. Conclusion: Our analysis showed that the secondary infection rate was higher among household contacts. This study suggests a dose-response association between severity of the primary case of SARS CoV-2 and infection among contacts.