ABSTRACT
Introduction: Health care workers (HCW) are exposed to SARS-CoV-2 through patient contact. Objectives: We aimed to assess the seroprevalence for SARS-CoV-2 among HCW in the canton Grisons and analyze risk factors associated with seroconversion. Methods: HCW from 13 health care institutions were recruited. Sera were analyzed for SARS-CoV-2 antibodies using an electro-chemiluminescence immunoassay of Roche Diagnostics in mid-2020 (survey I) and early 2021 (survey II). Participants reported risk factors for COVID-19 in a questionnaire.Odds ratios (OR) and 95% confidence intervals (95% CI) for the association of seropositivity with each risk factor were determined by logistic regression. Results: SARS-CoV2 serology was positive in 99 of 2794 (3.5%) participants in survey I and in 376 of 2315 (13.5%) participants in survey II. By survey II, 86 of 88 (97.7%) initially seropositive participants remained seropositive. In multivariable analysis of both surveys, the strongest association for SARS-CoV-2 seroconversion was contact with a household member with COVID-19 (adjusted OR: 21.2, 95% CI: 8.5-51.4, p < 0.001, survey I;aOR: 8.5, 95% CI: 6.0-12.1, p < 0.001, survey II). Significant occupational risk factors included contact with patients with COVID-19 in both surveys (aOR: 2.7, 95% CI: 1.4-5.4, p < 0.001, survey I and aOR: 1.4, 95% CI: 1.0-2.2, p = 0.046, survey II). Contact to a SARSCoV- 2 positive co-worker was a significant risk factor only in survey I, whereas private contact with SARS-CoV-2 positive persons and the COVID-19 incidence in the region of the HCI were associated with seroconversion only in survey II. Conclusion: Contact with patients with COVID-19 was an important risk factor for seroconversion, although the risk was higher for household contacts. These findings highlight the need to optimize preventive measures for SARS-CoV2 infection among HCW.