Seroprevalence of anti-SARS-CoV-2 antibodies and associated factors among household contacts of COVID-19 confirmed cases in Bangkok, Thailand

BACKGROUND: High COVID-19 transmission among household (HH) contacts of infected cases were reported with seroprevalence varying from 5.5% to 57.2% worldwide. Data on seroprevalence among HH contacts and factors associated with seropositivity in Thailand are limited. OBJECTIVES: To determine the seroprevalence and factors associated with anti-SARS-CoV-2 antibodies among HH contacts of COVID-19 confirmed cases. MATERIALS AND METHODS: Data on confirmed COVID-19 cases (primary cases) in Bangkok from March 2020–July 2021 were retrieved from Institute for Urban Disease Control and Prevention. Primary cases were contacted within 14 days of testing positive for permission to contact their HH contacts via telephone. HH contacts were then recruited to complete questionnaires about demographics, and risk factors and blood was collected and tested for total immunoglobulin antibody against SARS-CoV-2 spike S1 protein. Factors associated with seropositivity were analysed by logistic regression. RESULTS: Eligible participants of 452 HH contacts of infected cases in Bangkok were contacted. Seroprevalence was 20.5% among HH contacts. Factors associated with seropositivity after multivariate analysis were relationship to index case (being other relatives to index case (other than close relatives/spouse) [aOR 4.04, 95% CI; 1.15, 14.14, p.029] and being a co-worker to index cases [aOR 0.16, 95% CI; 0.045, 0.60, p.006]), always staying in the same room with index case [aOR 5.64, 95% CI; 1.95, 16.34, p.001], sharing utensil [aOR 0.25, 95% CI; 0.074, 0.82, p.023], and participation in leisure activities together with index case [aOR 4.77, 95% CI; 1.47, 15.51, p.009]. CONCLUSION: Serological investigation can be used in detecting COVID-19 infection in conjunction with other molecular techniques. It is a useful tool for studies on seroprevalence in a population as well as seroconversion after a vaccination campaign. Sharing living environments are associated with seropositivity in HH contacts. Nevertheless, individual practices can be affected by awareness, cultural differences, and control measures implemented by each country.