CD40LG and COVID-19: We used an outreach and contactless care service system to assess the prevalence of SARS-CoV-2 RNA positivity in nasopharyngeal/throat specimens and anti-SARS-CoV-2 IgM/IgG antibodies seroprevalence and the associated factors among at-risk populations in Chiang Mai and Lamphun provinces, Thailand, around the second wave of COVID-19 outbreak.