Assessment of infection status of virus causing COVID-19 in at-risk populations in Chiang Mai and Lamphun Provinces, Thailand, through an outreach and contactless care service system

Abstract

Non-healthcare workers with a high potential for exposure to severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) may contribute to SARS-CoV- 2 spreading. We assessed the prevalence of SARS-CoV-2 RNA positivity and anti-SARS- CoV-2 IgM/IgG, and potential associated factors among individuals with mild or no symptoms and with a high exposure risk in Chiang Mai and Lamphun provinces, Thailand during the second wave of epidemic. This cross-sectional study enrolled individuals at- risk of SARS-CoV-2 infection during November 2020 - January 2021. Socio- demographic data were collected through an on-line questionnaire prior to collection of nasopharyngeal/throat swab samples and blood samples that were tested for SARS-CoV- 2 RNA (DaAn Gene, China) and anti-SARS-CoV-2 IgM/IgG antibodies (commercial lateral flow immunoassays), respectively. Associated factors were analyzed using univariable and multivariable logistic regression analysis. Of 1,651 participants, 52% were females, the median age was 36.6 years, one-third were Myanmar. None of the participants was positive for SARS-CoV-2 RNA (95% CI: 0-0.2). Fourteen were positive for anti-SARS-CoV-2 IgM/IgG antibodies (0.9%, 95% CI: 0.5-1.4), including 7 positive for IgM and 7 positive for IgG (0.4%, 95% CI: 0.2-0.9). Being over 60 years was independently associated with virus exposure (OR: 17.0, 95% CI: 2.2-128.5%, p=0.006). Despite high exposure risk, no participant presented current infection, and a very high proportion was still susceptible to SARS-CoV-2 infection and thus would clearly benefit from vaccination. Continuing active surveillance, improving vaccination coverage and monitoring response to vaccine will help better control the COVID-19 spread.