Outbreaks Open Access
Like 0


In July 2018, a large outbreak of Legionnaires’ disease (LD) caused by 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.


Article metrics loading...

Loading full text...

Full text loading...



  1. Haubitz S, Hitz F, Graedel L, Batschwaroff M, Wiemken TL, Peyrani P, et al. Ruling out Legionella in community-acquired pneumonia. Am J Med. 2014;127(10):1010.e11-9.  https://doi.org/10.1016/j.amjmed.2014.03.042  PMID: 24813862 
  2. Garrison LE, Kunz JM, Cooley LA, Moore MR, Lucas C, Schrag S, et al. Vital signs: deficiencies in environmental control identified in outbreaks of Legionnaires’ disease — North America, 2000-2014. MMWR Morb Mortal Wkly Rep. 2016;65(22):576-84.  https://doi.org/10.15585/mmwr.mm6522e1  PMID: 27281485 
  3. European Centre for Disease Prevention and Control (ECDC). Annual epidemiological report for 2017. Legionnaires’ disease. Stockholm: ECDC; 2019. Available from: https://ecdc.europa.eu/sites/portal/files/documents/AER_for_2017-Legionnaires-disease_0.pdf
  4. Beauté JThe European Legionnaires’ Disease Surveillance Network. Legionnaires’ disease in Europe, 2011 to 2015. Euro Surveill. 2017;22(27).  https://doi.org/10.2807/1560-7917.ES.2017.22.27.30566  PMID: 28703097 
  5. Prussin AJ 2nd, Schwake DO, Marr LC. Ten questions concerning the aerosolization and transmission of Legionella in the built environment. Build Environ. 2017;123:684-95.  https://doi.org/10.1016/j.buildenv.2017.06.024  PMID: 29104349 
  6. Jernigan DB, Hofmann J, Cetron MS, Genese CA, Nuorti JP, Fields BS, et al. Outbreak of Legionnaires’ disease among cruise ship passengers exposed to a contaminated whirlpool spa. Lancet. 1996;347(9000):494-9.  https://doi.org/10.1016/S0140-6736(96)91137-X  PMID: 8596266 
  7. Hicks LA, Rose CE Jr, Fields BS, Drees ML, Engel JP, Jenkins PR, et al. Increased rainfall is associated with increased risk for legionellosis. Epidemiol Infect. 2007;135(5):811-7.  https://doi.org/10.1017/S0950268806007552  PMID: 17121693 
  8. Garcia-Vidal C, Labori M, Viasus D, Simonetti A, Garcia-Somoza D, Dorca J, et al. Rainfall is a risk factor for sporadic cases of Legionella pneumophila pneumonia. PLoS One. 2013;8(4):e61036.  https://doi.org/10.1371/journal.pone.0061036  PMID: 23613778 
  9. Chen NT, Chen MJ, Guo CY, Chen KT, Su HJ. Precipitation increases the occurrence of sporadic legionnaires’ disease in Taiwan. PLoS One. 2014;9(12):e114337.  https://doi.org/10.1371/journal.pone.0114337  PMID: 25474539 
  10. Rota MC, Caporali MG, Bella A, Scaturro M, Giannitelli S, Ricci ML. La legionellosi in Italia nel 2017. [Legionellosis in Italy in 2017]. Not Ist Super Sanità. 2018;31(9):7-12. Italian. Available from: https://www.iss.it/documents/20126/45616/nuovo_nov_2019ONLINE_15_.pdf/ea33e77d-e3a9-1c96-49a8-28d9fdc12506?t=1581097313618
  11. European Commission. Commission Implementing Decision (EU) 2018/945 of 22 June 2018 on the communicable diseases and related special health issues to be covered by epidemiological surveillance as well as relevant case definitions. Official Journal of the European Union. Luxembourg: Publications Office of the European Union 6.7.2018:L 170/1. Available from: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX%3A32018D0945&from=EN%29.
  12. International Organization for Standardization (ISO). ISO/TS 12869:2012. Water quality - Detection and quantification of Legionella spp and/or Legionella pneumophila by concentration and genic amplification by quantitative polymerase chain reaction (qPCR). Geneva: ISO; 2019. Available from: https://www.iso.org/standard/52079.html
  13. International Organization for Standardization (ISO). ISO 11731. Water Quality. Enumeration of Legionella. Geneva: ISO; 2017. Available from: https://www.iso.org/standard/61782.html
  14. Helbig JH, Kurtz JB, Pastoris MC, Pelaz C, Lück PC. Antigenic lipopolysaccharide components of Legionella pneumophila recognized by monoclonal antibodies: possibilities and limitations for division of the species into serogroups. J Clin Microbiol. 1997;35(11):2841-5.  https://doi.org/10.1128/JCM.35.11.2841-2845.1997  PMID: 9350744 
  15. European Working Group for Legionella Infections (EWGLI). The EWGLI SBT database for the typing of Legionella pneumophila. London: Public Health England; 2014. Available from: http://webarchive.nationalarchives.gov.uk/20190501130700/http://bioinformatics.phe.org.uk/legionella/legionella_sbt/php/sbt_homepage.php
  16. Maclure M. The case-crossover design: a method for studying transient effects on the risk of acute events. Am J Epidemiol. 1991;133(2):144-53.  https://doi.org/10.1093/oxfordjournals.aje.a115853  PMID: 1985444 
  17. Levy D, Lumley T, Sheppard L, Kaufman J, Checkoway H. Referent selection in case-crossover analyses of acute health effects of air pollution. Epidemiology. 2001;12(2):186-92.  https://doi.org/10.1097/00001648-200103000-00010  PMID: 11246579 
  18. Breslow N, Day N. Statistical methods in cancer research. Vol I: the analysis of case-control studies. Lyon: International Agency for Research on Cancer (IARC Scientific Publications No. 32); 1980.
  19. Lewallen S, Courtright P. Epidemiology in practice: case-control studies. Community Eye Health. 1998;11(28):57-8. PMID: 17492047 
  20. Bellasio R, Bianconi R, Mosca S, Zannetti P. Formulation of the Lagrangian particle model LAPMOD and its evaluation against Kincaid SF 6 and SO 2 datasets. Atmos Environ. 2017;163:87-98.  https://doi.org/10.1016/j.atmosenv.2017.05.039 
  21. Scire JS, Robe FR, Fernau ME, Yamartino RJ. A user’ s guide for the CALMET meteorological model. Version 5.0. Concord: Earth Tech, Inc; 2000. Available from: http://www.src.com/calpuff/download/CALMET_UsersGuide.pdf
  22. Schoen ME, Ashbolt NJ. An in-premise model for Legionella exposure during showering events. Water Res. 2011;45(18):5826-36.  https://doi.org/10.1016/j.watres.2011.08.031  PMID: 21924754 
  23. Nygård K, Werner-Johansen Ø, Rønsen S, Caugant DA, Simonsen Ø, Kanestrøm A, et al. An outbreak of legionnaires disease caused by long-distance spread from an industrial air scrubber in Sarpsborg, Norway. Clin Infect Dis. 2008;46(1):61-9.  https://doi.org/10.1086/524016  PMID: 18171215 
  24. Llasat MC. An objective classification of rainfall events on the basis of their convective features: application to rainfall intensity in the northeast of spain. Int J Climatol. 2001;21(11):1385-400.  https://doi.org/10.1002/joc.692 
  25. Russo A, Gouveia CM, Soares PMM, Cardoso RM, Mendes MT, Trigo RM. The unprecedented 2014 Legionnaires’ disease outbreak in Portugal: atmospheric driving mechanisms. Int J Biometeorol. 2018;62(7):1167-79.  https://doi.org/10.1007/s00484-018-1520-8  PMID: 29572569 
  26. García-Fulgueiras A, Navarro C, Fenoll D, García J, González-Diego P, Jiménez-Buñuales T, et al. Legionnaires’ disease outbreak in Murcia, Spain. Emerg Infect Dis. 2003;9(8):915-21.  https://doi.org/10.3201/eid0908.030337  PMID: 12967487 
  27. Castellani Pastoris M, Ciceroni L, Lo Monaco R, Goldoni P, Mentore B, Flego G, et al. Molecular epidemiology of an outbreak of Legionnaires’ disease associated with a cooling tower in Genova-Sestri Ponente, Italy. Eur J Clin Microbiol Infect Dis. 1997;16(12):883-92.  https://doi.org/10.1007/BF01700554  PMID: 9495668 
  28. Rota MC, Pontrelli G, Scaturro M, Bella A, Bellomo AR, Trinito MO, et al. Legionnaires’ disease outbreak in Rome, Italy. Epidemiol Infect. 2005;133(5):853-9.  https://doi.org/10.1017/S0950268805004115  PMID: 16181505 
  29. Haupt TE, Heffernan RT, Kazmierczak JJ, Nehls-Lowe H, Rheineck B, Powell C, et al. An outbreak of Legionnaires disease associated with a decorative water wall fountain in a hospital. Infect Control Hosp Epidemiol. 2012;33(2):185-91.  https://doi.org/10.1086/663711  PMID: 22227989 
  30. O’Loughlin RE, Kightlinger L, Werpy MC, Brown E, Stevens V, Hepper C, et al. Restaurant outbreak of Legionnaires’ disease associated with a decorative fountain: an environmental and case-control study. BMC Infect Dis. 2007;7(1):93.  https://doi.org/10.1186/1471-2334-7-93  PMID: 17688692 
  31. Beauté J, Sandin S, Uldum SA, Rota MC, Brandsema P, Giesecke J, et al. Short-term effects of atmospheric pressure, temperature, and rainfall on notification rate of community-acquired Legionnaires’ disease in four European countries. Epidemiol Infect. 2016;144(16):3483-93.  https://doi.org/10.1017/S0950268816001874  PMID: 27572105 
  32. Brandsema PS, Euser SM, Karagiannis I, Den Boer JW, Van Der Hoek W. Summer increase of Legionnaires’ disease 2010 in The Netherlands associated with weather conditions and implications for source finding. Epidemiol Infect. 2014;142(11):2360-71.  https://doi.org/10.1017/S0950268813003476  PMID: 24576486 
  33. Heuner K, Swanson M, editors. Legionella: molecular microbiology. Norwich: Caister Academic Press; 2008; 249 p.
  34. Agenzia regionale per la protezione dell’ambiente della Lombardia (ARPA Lombardia). Richiesta dati misurati - Meteorologia. [Request for measurement data – meteorology.] Milan: ARPA Lombardia. [Accessed: 18 May 2020]. Available from: https://www.arpalombardia.it:443/Pages/Meteorologia/Richiesta-dati-misurati.aspx
  35. Walker JT. The influence of climate change on waterborne disease and Legionella: a review. Perspect Public Health. 2018;138(5):282-6.  https://doi.org/10.1177/1757913918791198  PMID: 30156484 

Data & Media loading...

Submit comment
Comment moderation successfully completed
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error