SARS-CoV-2 Seroprevalence among a Southern U.S. Population Indicates Limited Asymptomatic Spread under Physical Distancing Measures

Abstract

Characterizing the asymptomatic spread of SARS-CoV-2 is important for understanding the COVID-19 pandemic. This study was aimed at determining asymptomatic spread of SARS-CoV-2 in a suburban, Southern U.S. population during a period of state restrictions and physical distancing mandates. This is one of the first published seroprevalence studies from North Carolina and included multicenter, primary care, and emergency care facilities serving a low-density, suburban and rural population since description of the North Carolina state index case introducing the SARS-CoV-2 respiratory pathogen to this population. To estimate point seroprevalence of SARS-CoV-2 among asymptomatic individuals over time, two cohort studies were examined. The first cohort study, named ScreenNC, was comprised of outpatient clinics, and the second cohort study, named ScreenNC2, was comprised of inpatients unrelated to COVID-19. Asymptomatic infection by SARS-CoV-2 (with no clinical symptoms) was examined using an Emergency Use Authorization (EUA)-approved antibody test (Abbott) for the presence of SARS-CoV-2 IgG. This assay as performed under CLIA had a reported specificity/sensitivity of 100%/99.6%. ScreenNC identified 24 out of 2,973 (0.8%) positive individuals among asymptomatic participants accessing health care during 28 April to 19 June 2020, which was increasing over time. A separate cohort, ScreenNC2, sampled from 3 March to 4 June 2020, identified 10 out of 1,449 (0.7%) positive participants. IMPORTANCE This study suggests limited but accelerating asymptomatic spread of SARS-CoV-2. Asymptomatic infections, like symptomatic infections, disproportionately affected vulnerable communities in this population, and seroprevalence was higher in African American participants than in White participants. The low, overall prevalence may reflect the success of shelter-in-place mandates at the time this study was performed and of maintaining effective physical distancing practices among suburban populations. Under these public health measures and aggressive case finding, outbreak clusters did not spread into the general population.

Disparities in SARS-CoV-2 seroprevalence among individuals presenting for care in central North Carolina over a six-month period

“…A previous study from central North Carolina that overlaps with the first two months of our study period found seroprevalence in an asymptomatic healthcare-seeking cohort below 1% using the Abbott nucleocapsid IgG assay. 5 This is much lower than the ∼3 % seropositive estimate in our cohort over this time period, and may be due to under-sampling of Latinx individuals in that study and/or preferential sampling of asymptomatic individual. There is also growing concern about the use and performance of nucleocapsid IgG assays in individuals with asymptomatic or mild disease.…”

“…One study of 4,422 asymptomatic inpatients and outpatients in central NC from April 28-June 19, 2020 found an estimated seroprevalence of 0 ·7 - 0·8%, and another study of 177,919 remnant clinical laboratory samples from routine screening (3,817 from NC) from July 27-September 24, 2020 found an estimated seroprevalence of 2·5 - 6·8%. 5,6 While overall seroprevalence estimates of a given study depend on sampling method, assay characteristics, geography, and temporal factors, seroprevalence studies can provide information on the spread of COVID-19 that is missed by looking at the number of confirmed acute cases alone.…”

Sero-prevalence of SARS-CoV-2 Antibody Among Adults in the General Population in Diredawa, Ethiopia

“…Our nding replicates ndings from a metaanalysis [26]. However, such effects were not reported in [25,28] probably related to the epidemic stage and different state of restrictions at the time these studies.…”

From Health Disparities to Hotspots to Public Health Strategies: The Impact of the COVID-19 Pandemic in North Carolina

“…It is still unknown whether and to what degree an antibody response indicates immunity to future infection, and reinfection with SARS-CoV-2 has been reported in a small number of persons [27]. A study conducted in North Carolina that enrolled outpatients and inpatients across a health system representing 267 different zip codes identified a low prevalence of 0.8% for SARS-CoV-2 based on antibody testing during late April through June [28]. A nationwide study reported that fewer than 10% of the adult population developed antibodies against SARS-CoV-2 during the first wave of the pandemic [29].…”

“…The NIH has also issued COVID-19 treatment guidelines for patients depending on the severity of illness, based on scientific data and review from an expert panel that includes members from North Carolina academic institutions [28]. For mild to moderate illness from COVID-19, there are no specific therapies for persons managed at home that have been formally recommended at this time.…”