Prevalence of IgG antibodies to SARS-CoV-2 among emergency department employees.

The prevalence of antibodies to SARS-CoV-2, the virus which causes Coronavirus disease 2019 (COVID-19), among healthcare personnel is unclear. A recent study noted an unadjusted prevalence of 1.5% of SARS-CoV-2 antibodies using a point of care test in a community surveillance study in Santa Clara, CA [1]. Other community surveillance projects have reported varying rates of COVID-19 antibody seropositivity, and were as high as 32% in an area of Boston considered a hot spot for COVID-19 [[2], [3], [4]]. Healthcare personnel may have a higher risk of exposure to COVID-19 than the general population. In this letter we report the findings of a voluntary program for SARS-CoV-2 antibody testing for faculty and staff at the University of Utah Hospital Emergency Department (ED), an urban, academic emergency department in Salt Lake City, Utah.

Between April 13 and 19, 2020, all ED employees were offered the opportunity to have serum testing performed for SARS-CoV-2 IgG antibodies. This program was not offered as a research protocol but was offered as a service to ED employees. All ED employees were eligible and participation was voluntary; employees were not selected for participation based on symptoms nor previous exposure to COVID-19. Testing was conducted through the university's regional pathology laboratory using the EUROIMMUN laboratory-performed semiquantitative Anti-SARS-CoV-2 ELISA for IgG. Local validation of the test yielded a sensitivity of 95.4% and a specificity of 98.3% [5]. Positive and indeterminate results were accompanied by a statement that the results did not indicate immunity to COVID-19 and employees should continue to wear full personal protective equipment when caring for patients with respiratory complaints.

Over the seven-day testing period, 279 ED employees participated in SARS-CoV-2 IgG testing. This group consisted of 68 emergency medicine technicians and paramedics, 102 nurses, 40 ancillary staff, and 69 physicians. This group represented 81.8% of the 341 ED employees eligible for participation. Testing has resulted for 270 ED employees (96.8%). Of these employees, 16 (5.9%) were positive SARS-CoV-2 IgG antibodies, 15 (5.6%) had an indeterminate result, and 239 (88.5%) had a negative result.

Testing occurred at a hospital that has admitted 48 patients with laboratory-confirmed COVID-19 and in a state with good access to RT-PCR testing for SARS-CoV-2. As of April 21, the state of Utah reported 3296 cases of laboratory-confirmed COVID-19 with 277 hospitalizations out of 72,358 individuals tested [6]. This equates to a statewide COVID-19 case rate of 103 cases per 100,000 population (0.1%). Relative to the presumed low number of sero-positive cases of COVID-19 in Utah, our cohort of ED personnel has a high rate of positive and indeterminate results for SARS-CoV-2 IgG antibodies. This is likely secondary to a greater probability of exposure to COVID-19-infected patients in the ED setting.

We recognize the limitations in both our methodology and results. We report only aggregate data from the testing, given that this was not a research protocol. We do not have additional information on the role, exposure history, nor previous COVID-19 testing among those who tested positive or indeterminate. As is the case with all current serum IgG testing in the United States, the test utilized is non-FDA approved and has yet to be fully validated. Additionally, the interpretation of serology results remains in question, given that even patients with a confirmed COVID-19 infection may have low or undetectable antibodies several weeks after infection [7].

In summary, we have found a high rate of SARS-CoV-2 IgG antibodies among ED employees relative to the presumed low rate of sero-positive COVID-19 cases in the state of Utah. We feel these results warrant further investigation into SARS-CoV-2 antibody prevalence among healthcare workers as well as assessment of employee exposure history and risk factors for infection.