• Luigi Vimercati, Pasquale Stefanizzi, Luigi De Maria, Antonio Caputi, Domenica Cavone, Marco Quarato, Loreto Gesualdo, Pier Luigi Lopalco, Giovanni Migliore, Stefania Sponselli, Giusi Graziano, Angela Maria Vittoria Larocca, and Silvio Tafuri.
• Interdisciplinary Department of Medicine, University of Bari, Bari, Italy; Occupational Medicine Unit, University Hospital of Bari, Bari, Italy. Electronic address: luigi.vimercati@uniba.it.
• Environ. Res. 2021 Apr 1; 195: 110793.

BackgroundHealthcare workers (HCWs) are highly exposed to SARS-CoV-2 infection given their specific tasks. The IgG-IgM serological assay has demonstrated good accuracy in early detection in symptomatic patients, but its role in the diagnosis of asymptomatic patients is uncertain. The aim of our study was to assess IgM and IgG prevalence in sera in a large cohort of HCWs previously subjected to Nasopharyngeal swab test (NST) after accurate risk assessment due to positive COVID-19 patient exposure during an observation period of 90 days.Methods2407 asymptomatic HCWs that had close contact with COVID-19 patients in the period between April 8th and June 7th were screened with NST based on the RT-PCR method. In parallel, they underwent large-scale chemiluminescence immunoassays involving IgM-IgG serological screening to determine actual viral spread in the same cohort.ResultsDuring the 90-day observation period, 18 workers (0.75%) resulted positive for SARS-CoV-2 infection at the NST, whereas the positivity rates for IgM and IgG were 11.51% and 2.37%, respectively (277 workers). Despite high specificity, serological tests were inadequate for detecting SARS-CoV-2 infection in patients with previous positive NST results (IgM and IgG sensitivities of 27.78% and 50.00%, respectively).ConclusionsThese findings indicate a widespread low viral load of SARS-CoV-2 among hospital workers. However, serological screening showed very low sensitivity with respect to NST in identifying infected workers, and negative IgG and IgM results should not exclude the diagnosis of COVID-19. IgG-IgM chemiluminescence immunoassays could increase the diagnosis of COVID-19 only in association with NST, and this association is considered helpful for decision-making regarding returning to work.Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.

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