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Bendavid, Eran; Mulaney, Bianca; Sood, Neeraj; Shah, Soleil; Bromley-Dulfano, Rebecca; Lai, Cara; Weissberg, Zoe; Saavedra-Walker, Rodrigo; Tedrow, Jim; Bogan, Andrew; Kupiec, Thomas; Eichner, Daniel; Gupta, Ribhav; Ioannidis, John P A; Bhattacharya, Jay

COVID-19 antibody seroprevalence in Santa Clara County, California

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  • Media type: E-Article
  • Title: COVID-19 antibody seroprevalence in Santa Clara County, California
  • Contributor: Bendavid, Eran; Mulaney, Bianca; Sood, Neeraj; Shah, Soleil; Bromley-Dulfano, Rebecca; Lai, Cara; Weissberg, Zoe; Saavedra-Walker, Rodrigo; Tedrow, Jim; Bogan, Andrew; Kupiec, Thomas; Eichner, Daniel; Gupta, Ribhav; Ioannidis, John P A; Bhattacharya, Jay
  • imprint: Oxford University Press (OUP), 2021
  • Published in: International Journal of Epidemiology
  • Language: English
  • DOI: 10.1093/ije/dyab010
  • ISSN: 1464-3685; 0300-5771
  • Origination:
  • Footnote:
  • Description: <jats:title>Abstract</jats:title> <jats:sec> <jats:title>Background</jats:title> <jats:p>Measuring the seroprevalence of antibodies to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is central to understanding infection risk and fatality rates. We studied Coronavirus Disease 2019 (COVID-19)-antibody seroprevalence in a community sample drawn from Santa Clara County.</jats:p> </jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>On 3 and 4 April 2020, we tested 3328 county residents for immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies to SARS-CoV-2 using a rapid lateral-flow assay (Premier Biotech). Participants were recruited using advertisements that were targeted to reach county residents that matched the county population by gender, race/ethnicity and zip code of residence. We estimate weights to match our sample to the county by zip, age, sex and race/ethnicity. We report the weighted and unweighted prevalence of antibodies to SARS-CoV-2. We adjust for test-performance characteristics by combining data from 18 independent test-kit assessments: 14 for specificity and 4 for sensitivity.</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>The raw prevalence of antibodies in our sample was 1.5% [exact binomial 95% confidence interval (CI) 1.1–2.0%]. Test-performance specificity in our data was 99.5% (95% CI 99.2–99.7%) and sensitivity was 82.8% (95% CI 76.0–88.4%). The unweighted prevalence adjusted for test-performance characteristics was 1.2% (95% CI 0.7–1.8%). After weighting for population demographics, the prevalence was 2.8% (95% CI 1.3–4.2%), using bootstrap to estimate confidence bounds. These prevalence point estimates imply that 53 000 [95% CI 26 000 to 82 000 using weighted prevalence; 23 000 (95% CI 14 000–35 000) using unweighted prevalence] people were infected in Santa Clara County by late March—many more than the ∼1200 confirmed cases at the time.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusion</jats:title> <jats:p>The estimated prevalence of SARS-CoV-2 antibodies in Santa Clara County implies that COVID-19 was likely more widespread than indicated by the number of cases in late March, 2020. At the time, low-burden contexts such as Santa Clara County were far from herd-immunity thresholds.</jats:p> </jats:sec>
  • Access State: Open Access