Abstract
Clinic-based estimates of SARS-CoV-2 may considerably underestimate the total number of infections. Access to testing in the US has been heterogeneous and symptoms vary widely in infected persons. Public health surveillance efforts and metrics are therefore hampered by underreporting. We set out to provide a minimally biased estimate of SARS-CoV-2 seroprevalence among adults for a large and diverse county (Orange County, CA, population 3.2 million). We implemented a surveillance study that minimizes response bias by recruiting adults to answer a survey without knowledge of later being offered SARS-CoV-2 test. Several methodologies were used to retrieve a population-representative sample. Participants (n = 2979) visited one of 11 drive-thru test sites from July 10th to August 16th, 2020 (or received an in-home visit) to provide a finger pin-prick sample. We applied a robust SARS-CoV-2 Antigen Microarray technology, which has superior measurement validity relative to FDA-approved tests. Participants include a broad age, gender, racial/ethnic, and income representation. Adjusted seroprevalence of SARS-CoV-2 infection was 11.5% (95% CI: 10.5–12.4%). Formal bias analyses produced similar results. Prevalence was elevated among Hispanics (vs. other non-Hispanic: prevalence ratio [PR] = 1.47, 95% CI 1.22–1.78) and household income < $50,000 (vs. > $100,000: PR = 1.42, 95% CI: 1.14 to 1.79). Results from a diverse population using a highly specific and sensitive microarray indicate a SARS-CoV-2 seroprevalence of ~ 12 percent. This population-based seroprevalence is seven-fold greater than that using official County statistics. In this region, SARS-CoV-2 also disproportionately affects Hispanic and low-income adults.
Highlights
Active and routine surveillance of infectious diseases serves a critical public health function by permitting estimation of overall prevalence and incidence of new infections[1,2]
This study represents a joint effort between University of California, Irvine (UCI) and the Orange County Health Care Agency (OCHCA)
Unlike available FDA authorized tests which detect antibodies against one or two a ntigens[17], the coronavirus antigen microarray (CoVAM) quantitatively measures IgG and IgM antibodies against 12 antigens from SARS-CoV-2, including spike (S) as whole protein or separated domains including S1, S2, and receptor-binding domain (RBD), nucleocapsid protein (NP), and membrane (M) protein (Supplemental Material Fig. S1)
Summary
Active and routine surveillance of infectious diseases serves a critical public health function by permitting estimation of overall prevalence and incidence of new infections[1,2]. Owing in part to limited testing capacity, no state in the US (including California) has enacted routine population-based surveillance of SARS-CoV-2. Since persons without (or with minor) symptoms may not seek care, and because testing capacity has frequently been limited, clinic-based estimates may considerably undercount the true incidence of SARSCoV-2 infections in the p opulation[6]. An ideal seroprevalence study design would recruit a representative sample from the population and detect SARS-CoV-2 (via antibodies from a blood test). To minimize selection bias and skewing of seroprevalence to people with suspected SARS-CoV-2 infection, serum samples would be obtained outside of a clinic without oversampling those who are more likely to have been infected (e.g., due to self-selection into a study based on knowledge of symptoms and being offered an antibody test). In addition to serving a critical surveillance function, we intend for our results to yield a more accurate measure of the infection fatality risk
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