Evolution of SARS-CoV-2 Seroprevalence Among Employees of a United States Academic Children’s Hospital During the COVID-19 Pandemic

Abstract Objectives: Describe cumulative seroprevalence of SARS-CoV-2 antibodies during the COVID-19 pandemic among employees of a large pediatric healthcare system. Design, Setting, and Participants: Prospective observational cohort study open to adult employees at Children’s Hospital of Philadelphia, conducted April 20 – December 17, 2020. Methods: Employees were recruited starting with high-risk exposure groups, utilizing emails, flyers, and announcements at virtual town halls. At baseline, 1-month, 2-month, and 6-month timepoints, participants reported occupational and community exposures and gave a blood sample for SARS-CoV-2 antibody measurement by enzyme-linked immunosorbent assays (ELISAs). A post hoc Cox proportional hazards regression model was performed to identify factors associated with increased risk for seropositivity. Results: 1740 employees were enrolled. At 6-months, cumulative seroprevalence was 5.3%, below estimated community point seroprevalence; seroprevalence was 5.8% and 3.4% among employees with and without direct patient care, respectively. Most participants seropositive at baseline remained positive at follow-up assessments. In post hoc analysis, direct patient care (HR: 1.95, 95% CI: 1.03 to 3.68), Black race (HR: 2.70, 95% CI: 1.24 to 5.87), and exposure to a confirmed case in a non-healthcare setting (HR: 4.32, 95% CI: 2.71 to 6.88) were associated with statistically significant increased risk for seropositivity. Conclusions: Employee SARS-CoV-2 seroprevalence rates remained below the surrounding community’s point prevalence rates. Provision of direct patient care, Black race, and exposure to a confirmed case in non-healthcare setting conferred increased risk. These data can inform occupational protection measures to maximize protection of employees within the workplace during future COVID waves or other epidemics.