Did symptomatic index cases propagate COVID-19 more effectively than the asymptomatic ones? Analysis of Phuket contact tracing data in the first half of 2020 and 2021

Abstract

Unlike SARS and MERS, COVID-19 had a stealth mode. This present study aims to compare the secondary attack rate among high-risk contacts exposed to symptomatic index cases with those exposed to asymptomatic ones. The chi-square statistic and logistic regression analysis are used to compare infection probabilities of HRCs who have been exposed to symptomatic and asymptomatic cases. Results indicate no statistical difference in infection probability between HRCs exposed to asymptomatic cases and HRCs exposed to symptomatic cases. This present study also revealed a significant impact of close contact with those who share the same household. The contacts in the same household of the index case had eightfold odds to the non-household of COVID-19 index cases, during the April 2020 wave, and fivefold odds during the April 2021 wave. We further recommend adding consistent active case finding as a prerequisite to eliminating both symptomatic and asymptomatic COVID-19 cases from households

Keywords

• asymptomatic transmission
• covid-19
• high-risk contact (hrc)
• household
• disease propagation