Large community-acquired Legionnaires' disease outbreak caused by Legionella pneumophila serogroup 1, Italy, July to August 2018

Marino Faccini, Antonio Giampiero Russo, Maira Bonini, Sara Tunesi, Rossella Murtas, Monica Sandrini, Sabrina Senatore, Anna Lamberti, Giorgio Ciconali, Serafina Cammarata, Eros Barrese, Valentina Ceriotti, Sonia Vitaliti, Marina Foti, Gabriella Gentili, Elisabetta Graziano, Emerico Panciroli, Marco Bosio, Maria Gramegna, Danilo CeredaCarlo Federico Perno, Ester Mazzola, Daniela Campisi, Gianuario Aulicino, Silvana Castaldi, Antonietta Girolamo, Maria Grazia Caporali, Maria Scaturro, Maria Cristina Rota, Maria Luisa Ricci

Research output: Contribution to journalArticlepeer-review


In July 2018, a large outbreak of Legionnaires' disease (LD) caused by Legionella pneumophila serogroup 1 (Lp1) occurred in Bresso, Italy. Fifty-two cases were diagnosed, including five deaths. We performed an epidemiological investigation and prepared a map of the places cases visited during the incubation period. All sites identified as potential sources were investigated and sampled. Association between heavy rainfall and LD cases was evaluated in a case-crossover study. We also performed a case-control study and an aerosol dispersion investigation model. Lp1 was isolated from 22 of 598 analysed water samples; four clinical isolates were typed using monoclonal antibodies and sequence-based typing. Four Lp1 human strains were ST23, of which two were Philadelphia and two were France-Allentown subgroup. Lp1 ST23 France-Allentown was isolated only from a public fountain. In the case-crossover study, extreme precipitation 5-6 days before symptom onset was associated with increased LD risk. The aerosol dispersion model showed that the fountain matched the case distribution best. The case-control study demonstrated a significant eightfold increase in risk for cases residing near the public fountain. The three studies and the matching of clinical and environmental Lp1 strains identified the fountain as the source responsible for the epidemic.

Original languageEnglish
Article number1900523
JournalEuro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin
Issue number20
Publication statusPublished - May 1 2020


  • Italy
  • Legionella pneumophila
  • legionnaires’ disease
  • outbreak

ASJC Scopus subject areas

  • Epidemiology
  • Public Health, Environmental and Occupational Health
  • Virology


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