PT - JOURNAL ARTICLE AU - Laura Milazzo AU - Alessia Lai AU - Laura Pezzati AU - Letizia Oreni AU - Annalisa Bergna AU - Federico Conti AU - Cristina Meroni AU - Davide Minisci AU - Massimo Galli AU - Mario Corbellino AU - Spinello Antinori AU - Anna Lisa Ridolfo TI - Dynamics of the seroprevalence of SARS-CoV-2 antibodies among healthcare workers at a COVID-19 referral hospital in Milan, Italy AID - 10.1136/oemed-2020-107060 DP - 2021 Aug 01 TA - Occupational and Environmental Medicine PG - 541--547 VI - 78 IP - 8 4099 - http://oem.bmj.com/content/78/8/541.short 4100 - http://oem.bmj.com/content/78/8/541.full SO - Occup Environ Med2021 Aug 01; 78 AB - Objectives Healthcare workers (HCWs) are at high risk of developing SARS-CoV-2 infection. The aim of this single-centre prospective study was to evaluate the trend of SARS-CoV-2 seroprevalence in HCWs working at the primary referral centre for infectious diseases and bioemergencies (eg, COVID-19) in Northern Italy and investigate the factors associated with seroconversion.Methods Six hundred and seventy-nine HCW volunteers were tested for anti-SARS-CoV-2 antibodies three times between 4 March and 27 May 2020 and completed a questionnaire covering COVID-19 exposure, symptoms and personal protective equipment (PPE) training and confidence at each time.Results SARS-CoV-2 seroprevalence rose from 3/679 to 26/608 (adjusted prevalence: 0.5%, 95% CI 0.1 to 1.7% and 5.4%, 95% CI 3.6 to 7.9, respectively) between the first two time points and then stabilised, in line with the curve of the COVID-19 epidemic in Milan. From the first time point, 61.6% of the HCWs had received training in the use of PPE and 17 (61.5%) of those who proved to be seropositive reported symptoms compatible with SARS-CoV-2 infection. Contacts with ill relatives or friends and self-reported symptoms were independently associated with an increased likelihood of seroconversion (p<0.0001 for both), whereas there was no significant association with professional exposure.Conclusion The seroprevalence of SARS-CoV-2 among the HCWs at our COVID-19 referral hospital was low at the time of the peak of the epidemic. The seroconversions were mainly attributable to extrahospital contacts, probably because the hospital readily adopted effective infection control measures. The relatively high number of asymptomatic seropositive HCWs highlights the need to promptly identify and isolate potentially infectious HCWs.Data are available on reasonable request. Anonymised participants data were collected in a protected database and are available on reasonable request from LM (laura.milazzo@asst-fbf-sacco.it) and ALR (annalisa.ridolfo@asst-fbf-sacco.it).