Risk of SARS-CoV-2 Acquisition in Health Care Workers According to Cumulative Patient Exposure and Preferred Mask Type

Health care workers (HCWs) are at increased risk for acquiring SARS-CoV-2 infection,¹ raising the issue of adequate protective measures. Although scientific evidence regarding the benefit of respirator vs surgical masks is sparse,^2,3 a previous study has suggested that respirator masks (ie, FFP2) may offer additional protection to HCW with frequent COVID-19-patient exposure.⁴ In this follow-up study, we analyzed the SARS-CoV-2 risk for HCWs depending on cumulative exposure to patients with COVID-19 and assessed whether this risk can be modulated by the use of respirator compared with surgical masks.

This cohort study was approved by the ethics committee of Eastern Switzerland. Written informed consent was obtained from participants. The study included volunteer HCWs from 7 health care networks in Northern and Eastern Switzerland.⁵ Baseline data (collected in September 2020) included anthropometric characteristics and job descriptions. In weekly follow-up evaluations during 12 months, participants indicated results of symptom-based SARS-CoV-2 nasopharyngeal swabs, exposures, and risk behavior (eMethods and eTable in the Supplement). In September 2021, participants indicated which mask type they had used in contact (if any) with patients with COVID-19 in the last 12 months outside of aerosol-generating procedures (among surgical mask only, both mask types, and respirators only). To assess cumulative patient exposure, we multiplied self-reported number of contacts with patients with COVID-19 (range, 0-100) and mean contact duration (range, 1-60 minutes). Cumulative patient exposure was grouped into 8 categories defined by powers of 2. At baseline, in January and September 2021, participants were screened for antinucleocapsid antibodies.⁵

The main outcome was SARS-CoV-2 infection during follow-up, ie, self-reported positive nasopharyngeal swab and/or antinucleocapsid seroconversion from baseline. Odds ratios (ORs) for the increase in SARS-CoV-2 positivity per doubling of contact time were calculated separately for HCWs using respirator masks only and those who used only surgical or both mask types. We used logistic regression to adjust for a priori–defined covariables and included networks as random effects (eMethods and eTable in the Supplement). Sensitivity analysis was performed excluding participants with positive households. R, version 3.6.1 (R Foundation for Statistical Analysis) was used for statistical analysis; 2-sided, unpaired P values <.05 were considered significant. This report follows STROBE reporting guideline for observational studies.

We included 2919 HCWs (median age, 43 years (range, 18-73 years); 749 participants (26%) were infected with SARS-CoV-2. SARS-CoV-2 positivity was 13% in HCWs without patient exposure. For those exposed to patients, positivity was 21% for HCWs using respirator masks and 35% for those using surgical/mixed masks (OR, 0.49; 95% CI, 0.39-0.61), showing an increase for surgical/mixed mask users (OR, 1.21; 95% CI, 1.15-1.28) and respirator mask users (OR, 1.15; 95% CI, 1.05-1.27) across categories of patient exposure (Figure). Variables associated with SARS-CoV-2 infection in multivariable analysis included a positive household contact (OR, 7.79; 95% CI, 5.98-10.15), exposure to patients (OR, 1.20 per category of cumulative contact; 95% CI, 1.14-1.26), respirator use (OR, 0.56; 95% CI, 0.43-0.74), and SARS-CoV-2 vaccination (OR, 0.55; 95% CI, 0.41-0.74) (Table). Similar results were obtained in sensitivity analysis.

In this study, SARS-CoV-2 positivity in HCWs was associated with cumulative COVID-19 patient exposure. The odds of being SARS-CoV-2–positive were reduced by more than 40% in individuals using respirators irrespective of cumulative exposure, even after adjusting for multiple work- and nonwork-related covariables.

These data suggest a dose-response association between COVID-19-patient exposure and risk of SARS-CoV-2 infection in HCWs. The presumable protection conferred by respirator use is in line with previous data.^1,4 Self-reporting of preferred mask type and residual confounding are potential study limitations.

Consequent use of respirators and SARS-CoV-2 vaccination might substantially decrease the work-related risk for HCWs exposed to patients with COVID-19. Whether these results are applicable to newer viral variants, which are more contagious and less neutralized by most vaccines,⁶ remains to be seen.

Accepted for Publication: June 27, 2022.

Published: August 15, 2022. doi:10.1001/jamanetworkopen.2022.26816

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2022 Dörr T et al. JAMA Network Open.

Corresponding Author: Philipp Kohler, MD, MSc, Division of Infectious Diseases and Hospital Epidemiology, Cantonal Hospital St Gallen, Rorschacherstrasse 95, 9007 St Gallen, Switzerland (philipp.kohler@kssg.ch).

Author Contributions: Dr Kohler had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Kahlert, Kohler.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Dörr, Kohler.

Critical revision of the manuscript for important intellectual content: Haller, Müller, Friedl, Vuichard, Kahlert, Kohler.

Statistical analysis: Dörr, Kohler.

Obtained funding: Kahlert, Kohler.

Administrative, technical, or material support: Friedl, Kahlert, Kohler.

Supervision: Haller, Kahlert, Kohler.

Conflict of Interest Disclosures: Dr Vuichard reported receiving nonfinancial support from Roche Diagnostics (Switzerland) AG. The company provided the Elecsys anti-SARS CoV-2 assays and additional ancillary products to the Thurgau Hospital Group. The company was not involved in the design or conduct of the study, nor was it involved in the content of the manuscript. During the conduct of the study. Dr Kohler reported receiving grants from Swiss National Sciences Foundation, grants from the Health Department of Canton of St Gallen, and grants from Swiss Federal Office of Public Health during the conduct of the study. No other disclosures were reported.

Funding/Support: This work was supported by the Swiss National Sciences Foundation (grants 31CA30_196544 and PZ00P3_179919 to Dr Kohler), the Federal Office of Public Health (grant 20.008218/421-28/1), and the Health Department of the Canton of St Gallen.

Role of the Funder/Sponsor: The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: Sabine Güsewell, PhD (Cantonal Hospital St Gallen), provided statistical advice; no financial compensation was provided. We thank the participants in the SURPRISE study and the members of the study group (in alphabetical order): Ulrike Besold, MD (Geriatric Clinic St Gallen), Angela Brucher, MD (Psychiatry Services South, St Gallen), Thomas Egger (Cantonal Hospital St Gallen), Andrée Friedl, MD (Cantonal Hospital Baden), Christian R. Kahlert, MD (Children’s Hospital of Eastern Switzerland, St Gallen), Philipp Kohler, MD, MSc (Cantonal Hospital St Gallen), Stefan P. Kuster, MD, MSc (Cantonal Hospital St Gallen), Onicio Leal, PhD (University of Zurich), Eva Lemmenmeier, MD (Clienia Littenheid), Allison McGeer, MD, MSc (Mount Sinai Hospital, Toronto), Dorette Meier Kleeb, MD (Cantonal Hospital Baden), J. Carsten Möller, MD (Clinic Zihlschlacht), Maja F. Müller (Hirslanden Clinic Zurich), Manuela Ortner (Rheintal Werdenberg Sarganserland Hospital Group, Grabs), Philip Rieder, PhD (Hirslanden Clinic Zurich), Lorenz Risch, MD, PhD (Laboratory Risch Buchs), Markus Ruetti, MD (Fuerstenland Toggenburg Hospital Group Wil), Matthias Schlegel, MD (Cantonal Hospital St Gallen), Hans-Ruedi Schmid, PhD (Cantonal Hospital Baden), Oliver Speer, PhD (Thurgau Hospital Group Muensterlingen), Reto Stocker, MD (Hirslanden Clinic Zurich), Pietro Vernazza, MD (Cantonal Hospital St Gallen), Matthias von Kietzell, MD (Clinic Stephanshorn St Gallen), Danielle Vuichard-Gysin, MD, MSc (Thurgau Hospital Group Muensterlingen), and Benedikt Wiggli, MD (Cantonal Hospital Baden).