Fiona P. Havers, Carrie Reed, Travis W. Lim, Joel M. Montgomery, John D. Klena, Aron J. Hall, Alicia M. Fry, Deborah L. Cannon, Cheng-Feng Chiang, Aridth Gibbons, Inna Krapiunaya,, Maria Morales-Betoulle, Katherine Roguski, Mohammed Rasheed, Brandi Freeman, Sandra Lester, Lisa Mills, Darin S. Carroll, S. Michelle Owen, Jeffrey A. Johnson, Vera A. Semenova, – State Collaborator Group, Jarad Schiffer, Natalie P. Thornburg
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.
To estimate prevalence of SARS-CoV-2 antibodies in convenience samples from several geographic sites in the United States.
Serologic testing of convenience samples using residual sera obtained for routine clinical testing by two commercial laboratory companies.
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.
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.