Incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in North Carolina from December 2020 - February 2022.

BACKGROUND: Surveillance estimates of SARS-CoV-2 infections over time have relied on mandatory clinician and laboratory reporting. These estimates increasingly underestimated true viral incidence due to asymptomatic infections, variable access to testing, and self-administered diagnostics. To overcome these limitations, the North Carolina Department of Health and Human Services partnered with academic researchers to conduct three concurrent population-based longitudinal cohort studies in three distinct North Carolina counties to offer more accurate estimates of the incidence, prevalence, and vaccination rates for SARS-CoV-2. METHODS: We enrolled and followed adult residents of three North Carolina counties from August 2020-February 2022. Demographic and health information was collected in biweekly surveys. Nasal swabs were collected biweekly and tested for SARS-CoV-2 using PCR testing. Blood samples were collected monthly and tested for antibodies to the SARS-CoV-2 nucleocapsid and spike proteins. We calculated monthly seroprevalence, sero-incidence, PCR test positivity, and vaccination uptake. RESULTS: We enrolled 646 participants. Routine blood samples and nasal swab samples were contributed by 639 and 642 participants, respectively. By February 2022, 98% (95% CI: 97.4-98.2) had antibodies to the SARS-CoV-2 spike protein, and 13% (95% CI: 12.4-14.2) had antibodies to the nucleocapsid protein, indicating viral exposure. PCR testing detected infection among 14% (95% CI: 13.1-15.0) of participants, but cumulative PCR test positivity was only 1.3% (95% CI: 1.2-1.4). Over half of PCR-detected infections were asymptomatic. By February 2022, 97% of participants had completed the primary vaccine series, and 52% had received a booster dose. CONCLUSIONS: Nearly all participants had anti-SARS-CoV-2 antibodies by the end of follow-up, primarily through vaccination. The incidence of PCR-detected infections was similar to antibody testing, but PCR test positivity substantially underestimated incident infections. These findings emphasize the importance of prospective infection monitoring via antibody testing in a comprehensive approach to tracking viral infections in the community setting.

Duke Scholars

Author Laura Kristin Newby Medicine, Cardiology

Author Christopher Wildrick Woods Medicine, Infectious Diseases

Author Coralei Neighbors  

Author Douglas Wixted