Prevalence of SARS-CoV-2 Infection Among Asymptomatic Health Care Workers in the Greater Houston, Texas, Area

Asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection continues to be a major public health concern.¹ Health care workers (HCWs) are at higher risk of infection and can become inadvertent vehicles of transmission.² Therefore, Houston Methodist initiated a coronavirus disease 2019 (COVID-19) surveillance program among asymptomatic HCWs and expanded to asymptomatic community residents. We report prevalence of SARS-CoV-2 among the first group tested.

This cross-sectional study was approved by the Houston Methodist institutional review board as part of a quality improvement project that includes a waiver of informed consent from HCWs, per institutional policy. Community residents were recruited via telephone, and written informed consent was obtained in person. This study is reported following the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

Houston Methodist comprises an academic medical center with 7 community hospitals treating patients with COVID-19. The HCWs included clinical employees in patient care areas, with and without patients with COVID-19, and nonclinical workers with no patient contact. Within COVID-19 units, certain job categories may have greater patient exposure, so we further classified COVID-19–facing HCWs into 5 job categories: (1) nursing (ie, registered nurses, nurse aides, bedside technicians, and emergency medical technicians), (2) clinicians (ie, physicians, residents, nurse practitioners, and physician assistants), (3) allied healthcare workers (ie, therapists, nonbedside technicians, pharmacists, and social workers), (4) support staff (ie, housekeeping and security), and (5) administrative or research staff (ie, managers, coordinators, administrative assistants, researchers, and research assistants).

From March 11 to April 19, 2020, we collected nasopharyngeal swabs, age, and sex information from self-reported asymptomatic HCWs and community residents. Testing was conducted via 1 of 3 cross-validated reverse transcriptase–polymerase chain reaction (RT-PCR) assays.

We report proportions with 95% CIs and used χ² proportional trend test to explore the association between SARS-CoV-2 positivity and HCW subgroups. We also provide logistic regression-based sex and age adjusted odds ratios (aORs) for SARS-CoV-2 positivity across 7 hospitals and 5 job categories among COVID-19–facing HCWs. Analyses were performed using Stata statistical software version 16 (StataCorp). P values were 2-sided, and statistical significance was set at .05.

A total of 2872 individuals, including 2787 HCWs and 85 community residents, were included; the mean (SD) age was 40.9 (11.7) years and 73% (95% CI, 71.6%-74.9%) were women. In all, 3.9% (95% CI, 3.2%-4.7%) tested positive for SARS-CoV-2. Among clinical HCWs, 5.4% (95% CI, 4.5%-6.5%) from COVID-19 units and 0.6% (95% CI, 0.2%-1.7%) from non–COVID units had RT-PCR test results positive for SARS-CoV-2 (aOR, 9.10; 95% CI, 3.33-24.82). None of the nonclinical HCWs or community residents had positive test results (P for trend <.001) (Table 1).

Among 1992 HCWs in units caring for patients with COVID-19, the rate of SARS-CoV-2 positivity ranged between 3.6% (95% CI, 1.3%-9.1%) for support staff to 6.5% (95% CI, 3.9%-10.7%) for allied health and 6.5% (95% CI, 3.6%-11.3%) for administrative staff. However, the proportions of participants with postive results for SARS-CoV-2 were not significantly different across the 5 job categories of COVID-19–facing HCWs (P for trend = .67).

After adjusting for age, sex, and job category, 2 hospitals demonstrated significantly higher likelihood of SARS-CoV-2 positivity among COVID-19–facing HCWs compared with the academic medical center (hospital 3: aOR, 2.78; 95% CI, 1.76-4.39; hospital 5: aOR, 2.49; 95% CI, 1.23-5.02), whereas the infection rate was significantly lower in another facility (hospital 2: aOR, 0.34; 95% CI, 0.12-0.95) (Table 2).

As COVID-19 pandemic reopening strategies are contemplated and enacted, understanding asymptomatic SARS-CoV-2 infection among HCWs is critical.^3,4 We report a 4.8% difference between COVID-19–facing (5.4%) and non–COVID-19–facing (0.6%) HCWs, potentially indicating transmission from patients or coworkers.^5,6 All nonclinical HCWs and community residents had RT-PCR test results negative for SARS-CoV-2. Nonclinical HCWs worked in buildings with separate entrances and heating, ventilation, and air conditioning systems, with lower population density due to remote working policies. Our comparison across job categories of COVID-19–facing HCWs did not yield significant differences between presumably high and low exposures, supporting the need for uniform infection control practices within patient care units.

Our findings are limited by convenience sampling from a single health care system and a small homogenous sample of community residents. However, higher infection rates among COVID-19–facing clinical HCWs and interhospital differences highlight the need for surveillance, isolation, and consistent infection control throughout an organization. Ongoing HCW surveillance is imperative to restore clinical operations.

Accepted for Publication: June 23, 2020.

Published: July 27, 2020. doi:10.1001/jamanetworkopen.2020.16451

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2020 Vahidy FS et al. JAMA Network Open.

Corresponding Author: Roberta L. Schwartz, PhD, Houston Methodist Academic Institute, 6670 Bertner Ave, Houston, TX 77030 (rlschwartz@houstonmethodist.org).

Author Contributions: Drs Vahidy and Schwartz had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Vahidy, Boom, Drews, Finkelstein, Schwartz.

Acquisition, analysis, or interpretation of data: Vahidy, Bernard, Drews, Christensen, Finkelstein, Schwartz.

Drafting of the manuscript: Vahidy, Bernard.

Critical revision of the manuscript for important intellectual content: Bernard, Boom, Drews, Christensen, Finkelstein, Schwartz.

Statistical analysis: Vahidy.

Obtained funding: Boom.

Administrative, technical, or material support: Bernard, Boom, Christensen, Schwartz.

Supervision: Boom, Drews, Schwartz.

Conflict of Interest Disclosures: None reported.

Additional Contributions: H. Dirk Sostman, MD; Bita A. Kash, PhD, MBA; and Robert A. Phillips, MD, PhD (Houston Methodist Academic Institute and Weil Cornell Medicine), provided leadership and overall supervision and guidance during all phases of this project, including design, operationalization, analysis, and writing. Firas Zabaneh, MBA (Houston Methodist), led project operationalization and infection control across the hospital system. Kimberly Greer, PhD (Houston Methodist Academic Institute), assisted with scientific writing. None of these individuals were compensated for their contributions.