Nasopharyngeal testing among healthcare workers (HCWs) of a large university hospital in Milan, Italy during two epidemic waves of COVID-19

Agnese Comelli, Dario Consonni, Andrea Lombardi, Giulia Viero, Massimo Oggioni, Patrizia Bono, Sara Colonia Uceda Renteria, Ferruccio Ceriotti, Davide Mangioni, Antonio Muscatello, Alessandra Piatti, Angela Cecilia Pesatori, Silvana Castaldi, Luciano Riboldi, Alessandra Bandera, Andrea Gori

Research output: Contribution to journalArticlepeer-review


Background: since October 2020, a second SARS-CoV-2 epidemic wave has hit Italy. We investigate the frequency of positive nasopharyngeal swabs among HCWs during the two waves and the association with occupation and demographic characteristics. Methods: this is a retrospective, observational study conducted in a large university hospital in Milan, Northern Italy. We defined two epidemic waves: 1st (February 2020–July 2020) and 2nd (August 2020–January 2021). Occupational and demographic characteristics of HCWs who underwent nasopharyngeal swabs for SARS-CoV-2 were collected. Results: in the 1st wave, 242 positive subjects (7.2%) were found among 3378 HCWs, whereas in the 2nd wave, the positive subjects were 545 out of 4465 (12.2%). In both epidemic waves positive NPSs were more frequent among HCWs with health-related tasks and lower among students (p < 0.001). However, in the 2nd wave, workers engaged in non-health-related tasks had a peak of 20.7% positivity. Among 160 positive HCWs in the 1st wave who were tested again in the 2nd wave, the rate of reinfection based on SARS-CoV2 RNA cycle quantification value was 0.6%. Conclusions: during the 2nd epidemic wave, we confirmed a significant impact of COVID-19 among HCWs. The rise of infection rate among HCWs seems to reflect the increasing spread of SARS-CoV-2 among the overall population.

Original languageEnglish
Article number8748
JournalInternational Journal of Environmental Research and Public Health
Issue number16
Publication statusPublished - Aug 2 2021


  • COVID-19
  • Healthcare operators
  • Nasopharyngeal swab
  • Reinfection
  • SARS-CoV-2

ASJC Scopus subject areas

  • Pollution
  • Public Health, Environmental and Occupational Health
  • Health, Toxicology and Mutagenesis


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