tetano
Editor, Senior Moderator
Int J Epidemiol
. 2021 Feb 22;dyab010.
doi: 10.1093/ije/dyab010. Online ahead of print.
COVID-19 antibody seroprevalence in Santa Clara County, California
Eran Bendavid[SUP] 1 [/SUP], Bianca Mulaney[SUP] 2 [/SUP], Neeraj Sood[SUP] 3 [/SUP], Soleil Shah[SUP] 2 [/SUP], Rebecca Bromley-Dulfano[SUP] 2 [/SUP], Cara Lai[SUP] 2 [/SUP], Zoe Weissberg[SUP] 2 [/SUP], Rodrigo Saavedra-Walker[SUP] 4 [/SUP], Jim Tedrow[SUP] 5 [/SUP], Andrew Bogan[SUP] 6 [/SUP], Thomas Kupiec[SUP] 7 [/SUP], Daniel Eichner[SUP] 8 [/SUP], Ribhav Gupta[SUP] 9 [/SUP], John P A Ioannidis[SUP] 1 9 [/SUP], Jay Bhattacharya[SUP] 1 [/SUP]
Affiliations
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.
Keywords: COVID-19; infection fatality rate; seroprevalence.
. 2021 Feb 22;dyab010.
doi: 10.1093/ije/dyab010. Online ahead of print.
COVID-19 antibody seroprevalence in Santa Clara County, California
Eran Bendavid[SUP] 1 [/SUP], Bianca Mulaney[SUP] 2 [/SUP], Neeraj Sood[SUP] 3 [/SUP], Soleil Shah[SUP] 2 [/SUP], Rebecca Bromley-Dulfano[SUP] 2 [/SUP], Cara Lai[SUP] 2 [/SUP], Zoe Weissberg[SUP] 2 [/SUP], Rodrigo Saavedra-Walker[SUP] 4 [/SUP], Jim Tedrow[SUP] 5 [/SUP], Andrew Bogan[SUP] 6 [/SUP], Thomas Kupiec[SUP] 7 [/SUP], Daniel Eichner[SUP] 8 [/SUP], Ribhav Gupta[SUP] 9 [/SUP], John P A Ioannidis[SUP] 1 9 [/SUP], Jay Bhattacharya[SUP] 1 [/SUP]
Affiliations
- PMID: 33615345
- DOI: 10.1093/ije/dyab010
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.
Keywords: COVID-19; infection fatality rate; seroprevalence.