Serologic Status and SARS-CoV-2 Infection over 6 Months of Follow Up in Healthcare Workers in Chicago: A Cohort Study.

OBJECTIVE: To determine the changes in severe acute respiratory coronavirus virus 2 (SARS-CoV-2) serologic status and SARS-CoV-2 infection rates in healthcare workers (HCWs) over 6-months of follow-up. DESIGN: Prospective cohort study. SETTING AND PARTICIPANTS: HCWs in the Chicago area. METHODS: Cohort participants were recruited in May and June 2020 for baseline serology testing (Abbott anti-nucleocapsid IgG) and were then invited for follow-up serology testing 6 months later. Participants completed monthly online surveys that assessed demographics, medical history, coronavirus disease 2019 (COVID-19), and exposures to SARS-CoV-2. The electronic medical record was used to identify SARS-CoV-2 polymerase chain reaction (PCR) positivity during follow-up. Serologic conversion and SARS-CoV-2 infection or possible reinfection rates (cases per 10,000 person days) by antibody status at baseline and follow-up were assessed. RESULTS: In total, 6,510 HCWs were followed for a total of 1,285,395 person days (median follow-up, 216 days). For participants who had baseline and follow-up serology checked, 285 (6.1%) of the 4,681 seronegative participants at baseline seroconverted to positive at follow-up; 138 (48%) of the 263 who were seropositive at baseline were seronegative at follow-up. When analyzed by baseline serostatus alone, 519 (8.4%) of 6,194 baseline seronegative participants had a positive PCR after baseline serology testing (4.25 per 10,000 person days). Of 316 participants who were seropositive at baseline, 8 (2.5%) met criteria for possible SARS-CoV-2 reinfection (ie, PCR positive >90 days after baseline serology) during follow-up, a rate of 1.27 per 10,000 days at risk. The adjusted rate ratio for possible reinfection in baseline seropositive compared to infection in baseline seronegative participants was 0.26 (95% confidence interval, 0.13-0.53). CONCLUSIONS: Seropositivity in HCWs is associated with moderate protection from future SARS-CoV-2 infection.

Seroprevalence and Correlates of SARS-CoV-2 Antibodies in Health Care Workers in Chicago.

BACKGROUND: Identifying factors associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among health care workers (HCWs) may help health systems optimize SARS-CoV-2 infection control strategies. METHODS: We conducted a cross-sectional analysis of baseline data from the Northwestern HCW SARS-CoV-2 Serology Cohort Study. We used the Abbott Architect Nucleocapsid IgG assay to determine seropositivity. Logistic regression models (adjusted for demographics and self-reported community exposure to coronavirus disease 2019 [COVID-19]) were fit to quantify the associations between occupation group, health care delivery tasks, and community exposure and seropositive status. RESULTS: A total of 6510 HCWs, including 1794 nurses and 904 non-patient-facing administrators, participated. The majority were women (79.6%), 74.9% were White, 9.7% were Asian, 7.3% were Hispanic, and 3.1% were non-Hispanic Black. The crude prevalence of seropositivity was 4.8% (95% CI, 4.6%-5.2%). Seropositivity varied by race/ethnicity as well as age, ranging from 4.2% to 9.6%. Out-of-hospital exposure to COVID-19 occurred in 9.3% of HCWs, 15.0% (95% CI, 12.2%-18.1%) of whom were seropositive; those with family members diagnosed with COVID-19 had a seropositivity rate of 54% (95% CI, 44.2%-65.2%). Support service workers (10.4%; 95% CI, 4.6%-19.4%), medical assistants (10.1%; 95% CI, 5.5%-16.6%), and nurses (7.6%; 95% CI, 6.4%-9.0%) had significantly higher seropositivity rates than administrators (referent; 3.3%; 95% CI, 2.3%-4.4%). However, after adjustment, nursing was the only occupation group with a significantly higher odds (odds ratio, 1.9; 95% CI, 1.3-2.9) of seropositivity. Exposure to patients receiving high-flow oxygen therapy and hemodialysis was significantly associated with 45% and 57% higher odds for seropositive status, respectively. CONCLUSIONS: HCWs are at risk for SARS-CoV-2 infection from longer-duration exposures to people infected with SARS-CoV-2 within health care settings and their communities of residence.