Seroprevalence of Antibodies to SARS-CoV-2 in Six Sites in the United States, March 23-May 3, 2020
Authors: Havers Fiona P. , Reed Carrie , Lim Travis , Montgomery Joel M. , Klena John D. , Hall Aron J. , Fry Alicia M. , Cannon Deborah L. , Chiang Cheng-Feng , Gibbons Aridth , Krapiunaya Inna , Morales-Betoulle Maria , Roguski Katherine , Rasheed Mohammad , Freeman Brandi , Lester Sandra , Mills Lisa , Carroll Darin S. , Owen S. Michele , Johnson Jeffrey A. , Semenova Vera ,   State Collaborator Group, Schiffer Jarad , Thornburg Natalie , Blackmore Carina , Blog Debra , Dunn Angela , Lindquist Scott , Pritchard Scott , Sosa Lynn , Turabelidze George , Wiesman John , Williams Randall W. 
Published: June 2020

Importance

Reported cases of SARS-CoV-2 infection likely underestimate the prevalence of infection in affected communities. Large-scale seroprevalence studies provide better estimates of the proportion of the population previously infected.

Objective

To estimate prevalence of SARS-CoV-2 antibodies in convenience samples from several geographic sites in the United States.

Design

Serologic testing of convenience samples using residual sera obtained for routine clinical testing by two commercial laboratory companies.

Setting

Connecticut (CT), south Florida (FL), Missouri (MO), New York City metro region (NYC), Utah (UT), and Washington State’s (WA) Puget Sound region.

Participants

Persons of all ages with serum collected during intervals from March 23 through May 3, 2020.

Exposure

SARS-CoV-2 virus infection.

Main outcomes and measures

We estimated the presence of antibodies to SARS-CoV-2 spike protein using an ELISA assay. We standardized estimates to the site populations by age and sex. Estimates were adjusted for test performance characteristics (96.0% sensitivity and 99.3% specificity). We estimated the number of infections in each site by extrapolating seroprevalence to site populations. We compared estimated infections to number of reported COVID-19 cases as of last specimen collection date.

Results

We tested sera from 11,933 persons. Adjusted estimates of the proportion of persons seroreactive to the SARS-CoV-2 spike protein ranged from 1.13% (95% confidence interval [CI] 0.70-1.94) in WA to 6.93% (95% CI 5.02-8.92) in NYC (collected March 23-April 1). For sites with later collection dates, estimates ranged from 1.85% (95% CI 1.00-3.23, collected April 6-10) for FL to 4.94% (95% CI 3.61-6.52) for CT (April 26-May 3). The estimated number of infections ranged from 6 to 24 times the number of reported cases in each site.

Conclusions and relevance

Our seroprevalence estimates suggest that for five of six U.S. sites, from late March to early May 2020, >10 times more SARS-CoV-2 infections occurred than the number of reported cases. Seroprevalence and under-ascertainment varied by site and specimen collection period. Most specimens from each site had no evidence of antibody to SARS-CoV-2. Tracking population seroprevalence serially, in a variety of specific geographic sites, will inform models of transmission dynamics and guide future community-wide public health measures.

Key findings

Question

What proportion of persons in six U.S. sites had detectable antibodies to SARS-CoV-2, March 23-May 3, 2020?

Findings

We tested 11,933 residual clinical specimens. We estimate that from 1.1% of persons in the Puget Sound to 6.9% in New York City (collected March 23-April 1) had detectable antibodies. Estimates ranged from 1.9% in south Florida to 4.9% in Connecticut with specimens collected during intervals from April 6-May 3. Six to 24 times more infections were estimated per site with seroprevalence than with case report data.

Meaning

For most sites, evidence suggests >10 times more SARS-CoV-2 infections occurred than reported cases. Most persons in each site likely had no detectable SARS-CoV-2 antibodies.