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

Abstract

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.

Keywords: COVID-19; SARS-CoV-2; health care workers; serology.

Figure 1.

Timeline of Northwestern Medicine COVID-19 Inpatient Census, Chicago case rate, and state government response during the local accelerated phase of the pandemic. A, Northwestern Medicine COVID-19 in-patient admitted patients from 3/1/2020 through 8/6/2020. B, Chicago COVID-19 case rate by date. Cases are presented as case/100 000 population. Abbreviations: COVID-19, coronavirus disease 2019; NM HCW, Northwestern Medicine health care worker.

Figure 2.

Unadjusted and multivariable adjusted^a logistic regression models of the association between anti-SARS-CoV-2-seropositive status and (A) out-of-hospital exposures,^b (B) occupation group,^c and (C) clinical care tasks.^{d a}Multivariable adjustment including age, race/ethnicity, and gender (red) or age, race/ethnicity, gender, and variable for nonhospital exposure (blue). ^bOut-of-hospital exposures: For the question on whether the participant reported a family member having a COVID-19 test, the reference group is family did not have a test. For the question on whether the participant reported an exposure to COVID-19 outside the hospital, no reported nonhospital exposure is the reference. ^cThe reference group for occupations is administrators. ^dFor the question on whether the participant reported exposure to a patient with COVID-19, the reference is no exposure to a patient with COVID-19. For the question on whether a participant conducted a procedure or a specific procedure, the reference is no or not that specific procedure. Abbreviations: CLP, central line placement; COVID-19, coronavirus disease 2019; PT/OT, physical therapy/occupational therapy; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; TEE, transesophageal echocardiography; TTE, transthoracic echocardiography.

Figure 3.

Heat map of Chicago neighborhoods and surrounding counties by seropositive rate for NM HCW and Chicagoland COVID-19 case rate data. Range of % positive IgG across neighborhoods is on the left. COVID-19 case rates from the Illinois Department of Public Health as of June 15, 2020, is on the right. Darker colors represent higher IgG/case % rates, and lighter represent lower IgG/case + rates. Abbreviations: COVID-19, coronavirus disease 2019; IgG, immunoglobulin G; NM HCW, Northwestern Medicine health care worker.