SARS-CoV-2 Seroprevalence Survey Among District Residents Presenting for Serologic Testing at Three Community-Based Test Sites — Washington, DC, July–August, 2020

BackgroundThe District of Columbia (DC), a major metropolitan area, continues to see community transmission of SARS-CoV-2. While serologic testing does not indicate current SARS-CoV-2 infection, it can indicate prior infection and help inform local policy and health guidance. The DC Department of Health (DC Health) conducted a community-based survey to estimate DCs SARS-CoV-2 seroprevalence and identify seropositivity-associated factors. MethodsA mixed-methods cross-sectional serology survey was conducted among a convenience sample of DC residents during July 27-August 21, 2020. Free serology testing was offered at three public test sites. Participants completed an electronic questionnaire on household and demographic characteristics, COVID-like illness (CLI) since January 1, 2020, comorbidities, and SARS-CoV-2 exposures. Univariate and bivariate analyses were conducted to describe the sample population and assess factors associated with seropositivity. ResultsAmong a sample of 671 participants, 51 individuals were seropositive, yielding an estimated seroprevalence of 7.6%. More than half (56.9%) of the seropositive participants reported no prior CLI; nearly half (47.1%) had no prior SARS-CoV-2 testing. Race/ethnicity, prior SARS-CoV-2 testing, prior CLI, employment status, and contact with confirmed COVID-19 cases were associated with seropositivity (P<0.05). Among those reporting prior CLI, loss of taste or smell, duration of CLI, fewer days between CLI and serology test, or prior viral test were associated with seropositivity (P[≤]0.006). ConclusionsThese findings indicate many seropositive individuals reported no symptoms consistent with CLI since January or any prior SARS-CoV-2 testing. This underscores the potential for cases to go undetected in the community and suggests wider-spread transmission than previously reported in DC. What is already known on this subject?Traditional case-based detection and syndromic surveillance efforts might not identify mildly symptomatic or asymptomatic SARS-CoV-2 infections. This is particularly true among people in the general population who do not have increased risk of severe illness or might not be tested otherwise. Consequently, the true population prevalence of prior SARS-CoV-2 infections might not be known. What this study adds?A community-based seroprevalence survey conducted in Washington, DC, during July 27-August 21, 2020 estimated that 7.6% of the convenience sample had antibodies to SARS-CoV-2, indicating prior infection. At the time of this survey, most of the participants reported that they had not been previously infected with or tested for SARS-CoV-2. These findings highlight both the value of serologic surveillance in complementing other surveillance methods, and the importance of continued prevention and mitigation measures, such as maintaining physical distances of at least 6 feet, avoiding crowds and poorly ventilated spaces, practicing frequent hand hygiene, and wearing face masks properly and consistently around people who do not live with you.