Severe Acute Respiratory Syndrome Coronavirus 2 Cumulative Incidence, United States, August 2020–December 2020

Abstract

Reported COVID-19 cases underestimate SARS-CoV-2 infections. We conducted a national probability survey of US households to estimate the cumulative incidence adjusted for antibody waning. From August-December 2020, a multistage random sample of US addresses were mailed a survey and materials to self-collect nasal swabs and dried blood spots. One adult household member completed the survey and mail specimens for viral detection with PCR and total (IgA, IgM, IgG) nucleocapsid antibody by a commercial, EUA-approved antigen capture assay. We estimated cumulative incidence of SARS-CoV-2 adjusted for waning antibodies and calculated reported fraction and infection fatality ratio (IFR). Differences in seropositivity among demographic, geographic and clinical subgroups were explored with weighted prevalence ratios (PR). Among 39,500 sampled households, 4,654 respondents provided responded. Cumulative incidence adjusted for waning was 11.9% (95% credible interval (CrI): 10.5-13.5%) as of October 30, 2020. We estimated 30,332,842 (CrI: 26,703,753- 34,335,338) total infections in the U.S. adult population by October 30, 2020. Reported fraction was 17% and IFR was 0.85% among adults. Non-Hispanic Black (PR: 2.2) and Hispanic (PR: 3.1) persons were more likely than White non-Hispanic to be seropositive, as were those living in metropolitan areas (PR: 2.5). One in 8 US adults had been infected with SARS-CoV-2 by late October 2020; but few had been accounted for in public health reporting. The scope of the COVID-19 pandemic is likely substantially underestimated by reported cases. Disparities in COVID-19 by race observed among reported cases cannot be attributed to differential diagnosis or reporting of infections in some population subgroups.