COVID-19 antibody seroprevalence in santa clara county, california
Open accessPublished version of a preprint
Abstract
BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.
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Recent studies demonstrated that the spread of COVID-19 exceeded what was reported based on RT-PCR testing.
“recent studies demonstrated that the spread of COVID-19 exceeded what was reported based on real-time polymerase chain reaction (RT-PCR) testing [11].”
From Seroprevalence of COVID-19 and Psychological Distress among Front Liners at the Universiti Malaysia Sabah Campus during the Third Wave of COVID-19 (2022) · cites this paper as [11]
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“Nevertheless, serological detection of specific antibodies against SARS-CoV-2 could help to better estimate the true number of infections and inform public health interventions; recent studies demonstrated that the spread of COVID-19 exceeded what was reported based on real-time polymerase chain reaction (RT-PCR) test…”
Background
- Authors
- Bendavid, E., Mulaney, B., Sood, N., Shah, S., Bromley-Dulfano, R., Lai, C., Weissberg, Z., Saavedra-Walker, R., Tedrow, J., Bogan, A., Kupiec, T., Eichner, D., Gupta, R., Ioannidis, J. P. A., & Bhattacharya, J.
- Affiliations
- Stanford Medicine (US)
- University of Southern California (US)
- Health Education is Power, Inc., Palo Alto, CA, USA
- The Compliance Resource Group, Inc., Oklahoma City, OK, USA
- Bogan Associates, LLC, Palo Alto, CA, USA
- Corresponding author
- Bendavid, Eran
- ORCID
- Venue
- International Journal of Epidemiology
- Publisher
- Oxford University Press (OUP)
- Published
- 2021-02-22
- Volume
- 50
- Issue
- 2
- Pages
- 410-419
- ISSN
- 0300-5771 (ISSN-L)
- 1464-3685
- PMC
- PMC7928865
- OpenAlex
- W3129346638
- Cited by
- 669
- References
- 29
- Citations by year
- 2026: 4 · 2025: 21 · 2024: 16 · 2023: 48 · 2022: 83 · 2021: 156 · 2020: 341
- FWCI
- 23.92
- Type
- journal article
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- Locations
- International Journal of Epidemiology (publishedVersion, cc-by-nc)
- medRxiv (acceptedVersion, cc-by-nc-nd)
- PubMed Central (publishedVersion, cc-by-nc)
- PubMed (publishedVersion)
- Funders
- Stanford COVID-19 Seroprevalence Studies Fund
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 detection and testing
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Keywords
- COVID-19 seroprevalence, SARS-CoV-2, COVID-19 pandemic, seroprevalence, IgM and IgG antibodies, Santa Clara County, lateral flow assay, assay sensitivity and specificity, prevalence estimation, unreported infections, population weighting
- MeSH terms
- COVID-19, SARS-CoV-2, Antibodies, Viral, California, Humans, Seroepidemiologic Studies
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