SARS-CoV-2 Seroprevalence Survey Among District Residents Presenting for Serologic Testing at Three Community-Based Test Sites — Washington, DC, July–August, 2020
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Abstract
Background
The 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 DC’s SARS-CoV-2 seroprevalence and identify seropositivity-associated factors.
Methods
A 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.
Results
Among 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).
Conclusions
These 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.
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SciScore for 10.1101/2021.02.15.21251764: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization Initially, a two-stage cluster sampling design was implemented to obtain a representative sample of 560 randomly selected households (Figure 1). Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Antibodies Sentences Resources Serologic testing was conducted using the DiaSorin LIAISON® XL assay (DiaSorin Inc., Stillwater, MN), a qualitative chemiluminescent assay for determination of IgG antibodies to the spike protein (anti-S1 and anti-S2) of SARS-CoV-2. anti-S1suggested: Noneanti-S2suggested: NoneDifferences in demographic, clinical and other descriptive characteristics between … SciScore for 10.1101/2021.02.15.21251764: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization Initially, a two-stage cluster sampling design was implemented to obtain a representative sample of 560 randomly selected households (Figure 1). Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Antibodies Sentences Resources Serologic testing was conducted using the DiaSorin LIAISON® XL assay (DiaSorin Inc., Stillwater, MN), a qualitative chemiluminescent assay for determination of IgG antibodies to the spike protein (anti-S1 and anti-S2) of SARS-CoV-2. anti-S1suggested: Noneanti-S2suggested: NoneDifferences in demographic, clinical and other descriptive characteristics between participants with (seropositive) and without (seronegative) SARS-CoV-2 IgG antibodies were assessed using Wilcoxon rank-sum tests for continuous variables, and Fisher’s exact tests or Pearson’s chi-squared tests for categorical variables. SARS-CoV-2 IgGsuggested: NoneSoftware and Algorithms Sentences Resources All analyses were conducted using SAS (version 9.4; SAS Institute). SAS Institutesuggested: (Statistical Analysis System, RRID:SCR_008567)Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:There are several limitations of this survey. Most notably, the low response rates of mailed invitations led to a reliance on convenience sampling and results are, therefore, not generalizable to the DC population. The use of a convenience sample likely inflated the seroprevalence estimate due to self-selection bias. Test sites’ hours of operation were restricted to weekday business hours, which made participation difficult for those currently employed, particularly in an essential job. The testing sites also remained in fixed locations, which made access less convenient for certain census blocks in DC. Additionally, the current analysis did not account for clustering within a household, as the average number of individuals per enrolled household was 1.3 persons. Inclusion of multiple individuals from the same household was possible, and multiple positive results were observed among 4 of the 44 households with at least one seropositive result. Since IgG antibodies can take 14 days PSO to reach detectable limits, it is possible that persons with an acute infection had not yet produced detectable levels of SARS-CoV-2 antibodies, particularly among people tested within 14 days PSO. Further, as immunological assessments found that not all individuals mount an antibody response following SARS-CoV-2 infection, it is possible that some participants might have had a previous SARS-CoV-2 infection, but did not produce detectable antibodies and, thus, were not identified through serolog...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
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