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Seroprevalence of and Risk Factors Associated With SARS-CoV-2 Infection in Health Care Workers During the Early COVID-19 Pandemic in Italy

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To identify the key insights or developments described in this article
1 Credit CME
Key Points

Question  What are the seroprevalence and the relative odds of SARS-CoV-2 infection among health care workers (HCWs) employed in different professional categories and operational units?

Findings  In this cross-sectional study of 82 961 serological tests of Italian HCWs, 12.2% of participants were positive for IgG antibodies against SARS-CoV-2. Higher odds of infection were found among nurses, health assistants, and workers enrolled in emergency departments or in treatment of patients with subacute disease.

Meaning  These findings suggest that equipment and training of personnel less accustomed to managing infectious disease but directly exposed to patients who may be infected with SARS-CoV-2 should be prioritized to decrease infection risks in health care settings.


Importance  Identifying health care settings and professionals at increased risk of SARS-CoV-2 infection is crucial to defining appropriate strategies, resource allocation, and protocols to protect health care workers (HCWs) and patients. Moreover, such information is crucial to decrease the risk that HCWs and health care facilities become amplifiers for SARS-CoV-2 transmission in the community.

Objective  To assess the association of different health care professional categories and operational units, including in-hospital wards, outpatient facilities, and territorial care departments, with seroprevalence and odds of SARS-CoV-2 infection.

Design, Setting, and Participants  This cross-sectional study was conducted using IgG serological tests collected from April 1 through May 26, 2020, in the Lombardy region in Italy. Voluntary serological screening was offered to all clinical and nonclinical staff providing any health care services or support to health care services in the region. Data were analyzed from June 2020 through April 2021.

Exposures  Employment in the health care sector.

Main Outcomes and Measures  Seroprevalence of positive IgG antibody tests for SARS-CoV-2 was collected, and odds ratios of experiencing infection were calculated.

Results  A total of 140 782 professionals employed in the health sector were invited to participate in IgG serological screening, among whom 82 961 individuals (59.0% response rate) were tested for SARS-CoV-2 antibodies, with median (interquartile range [IQR]; range) age, 50 (40-56; 19-83) years and 59 839 (72.1%) women. Among these individuals, 10 115 HCWs (12.2%; 95% CI, 12.0%-12.4%) had positive results (median [IQR; range] age, 50 [39-55; 20-80] years; 7298 [72.2%] women). Statistically significantly higher odds of infection were found among health assistants (adjusted odds ratio [aOR], 1.48; 95% CI, 1.33-1.65) and nurses (aOR, 1.28; 95% CI, 1.17-1.41) compared with administrative staff and among workers employed in internal medicine (aOR, 2.24; 95% CI, 1.87-2.68), palliative care (aOR, 1.84; 95% CI, 1.38-2.44), rehabilitation (aOR, 1.59; 95% CI, 1.33-1.91), and emergency departments (aOR, 1.56; 95% CI, 1.29-1.89) compared with those working as telephone operators. Statistically significantly lower odds of infection were found among individuals working in forensic medicine (aOR, 0.40; 95% CI, 0.19-0.88), histology and anatomical pathology (aOR, 0.71; 95% CI, 0.52-0.97), and medical device sterilization (aOR, 0.54; 95% CI, 0.35-0.84) compared with those working as telephone operators. The odds of infection for physicians and laboratory personnel were not statistically significantly different from those found among administrative staff. The odds of infection for workers employed in intensive care units and infectious disease wards were not statistically significantly different from those of telephone operators.

Conclusions and Relevance  These findings suggest that professionals partially accustomed to managing infectious diseases had higher odds of SARS-CoV-2 infection. The findings further suggest that adequate organization of clinical wards and personnel, appropriate personal protective equipment supply, and training of all workers directly and repeatedly exposed to patients with clinical or subclinical COVID-19 should be prioritized to decrease the risk of infection in health care settings.

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Article Information

Accepted for Publication: May 3, 2021.

Published: July 6, 2021. doi:10.1001/jamanetworkopen.2021.15699

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Poletti P et al. JAMA Network Open.

Corresponding Authors: Piero Poletti, Center for Health Emergencies, Bruno Kessler Foundation, via Sommarive 18, Povo, Trento 38123, Italy (poletti@fbk.eu); Marcello Tirani, Directorate General for Health, Lombardy region, via Indipendenza 3, 27100, Milan, Italy (marcello_tirani@regione.lombardia.it).

Author Contributions: Drs Poletti and Tirani 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. Dr Ajelli and Mr Merler are joint senior authors.

Concept and design: Poletti, Melegaro, Ajelli, Merler.

Acquisition, analysis, or interpretation of data: Tirani, Cereda, Trentini, Guzzetta, Marziano, Toso, Piatti, Piccarreta, Melegaro, Andreassi, Gramegna, Ajelli.

Drafting of the manuscript: Poletti, Melegaro.

Critical revision of the manuscript for important intellectual content: Tirani, Cereda, Trentini, Guzzetta, Marziano, Toso, Piatti, Piccarreta, Melegaro, Andreassi, Gramegna, Ajelli, Merler.

Statistical analysis: Poletti, Trentini.

Administrative, technical, or material support: Andreassi, Gramegna.

Supervision: Poletti, Tirani, Cereda, Toso, Melegaro, Ajelli, Merler.

Conflict of Interest Disclosures: Dr Ajelli reported receiving funding for research not related to COVID-19 from Seqirus outside the submitted work. No other disclosures were reported.

Funding/Support: Drs Poletti and Guzzetta and Mr Merler acknowledge receiving funding from the European Commission H2020 project Monitoring Outbreak Events for Disease Surveillance in a Data Science Context. Drs Poletti and Guzzetta and Mr Merler acknowledge receiving funding from the Fondazione Valorizzazione Ricerca Trentina Trento project Epidemiologia e Transmissione di COVID-19 in Trentino.

Role of the Funder/Sponsor: The funders 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.

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