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Abstract

BACKGROUND

Community-acquired Legionnaires’ disease (LD) has increased globally, including Europe. Climatic exposures may contribute to this rise, yet evidence from high-incidence countries, such as Italy, is limited.

AIM

We aimed to assess LD seasonality at the national level and the effects of temperature, relative humidity and precipitation on LD incidence at the municipality level.

METHODS

We analysed data on notified community-acquired LD cases and national climatic data from 2005 to 2023. Seasonality was assessed (peak-to-trough ratio (PTR)). A case time-series design with distributed lag nonlinear models was applied to estimate 1–10 week lagged effects of climatic exposures on LD incidence at the municipality level, as incidence rate ratios (IRRs).

RESULTS

Of the 28,662 notified LD cases, 27,458 (95.8%) were included. A clear seasonality was observed in the incidence, with a trough in early spring and a peak in autumn (PTR = 3.62; 95% confidence interval (CI): 2.45–5.34). Higher temperature and relative humidity had the strongest effects 10–9 weeks before disease onset (for 5°C increase above 15°C: IRR = 1.45; 95% CI: 1.33–1.58 and for 5% increase above 60%: IRR = 1.19; 95% CI: 1.12–1.26). Precipitation showed more immediate effects, particularly with a 1-week lag (for 5 mm increase above 10 mm: IRR = 1.07; 95% CI: 1.06–1.09). Findings were consistent among individuals aged ≥ 60 years.

CONCLUSION

A clear seasonal pattern was seen in the LD incidence, peaking in summer and autumn. Temperature and humidity increased LD risk over longer lags, while precipitation had shorter-term effects, suggesting climatic exposures influence environmental proliferation and immediate transmission of .

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2026-03-26
2026-04-21
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References

  1. Cunha BA, Burillo A, Bouza E. Legionnaires’ disease. Lancet. 2016;387(10016):376-85.  https://doi.org/10.1016/S0140-6736(15)60078-2  PMID: 26231463 
  2. Pareek A, Singhal R, Pareek A, Chuturgoon A, Sah R, Apostolopoulos V. Global surge of Legionnaires’ disease in 2024: urgent call for heightened awareness and preparedness. Lancet Microbe. 2025;6(4):101031.  https://doi.org/10.1016/j.lanmic.2024.101031  PMID: 39612922 
  3. Barskey AE, Derado G, Edens C. Rising incidence of Legionnaires’ disease and associated epidemiologic patterns, United States, 1992-2018. Emerg Infect Dis. 2022;28(3):527-38.  https://doi.org/10.3201/eid2803.211435  PMID: 35195513 
  4. European Centre for Disease Prevention and Control (ECDC). Legionnaires’ disease - Annual Epidemiological Report for 2021. Stockholm: ECDC; 3 Jul 2023. Available from: ecdc.europa.eu/en/publications-data/legionnaires-disease-annual-epidemiological-report-2021
  5. Moffa MA, Rock C, Galiatsatos P, Gamage SD, Schwab KJ, Exum NG. Legionellosis on the rise: A scoping review of sporadic, community-acquired incidence in the United States. Epidemiol Infect. 2023;151:e133.  https://doi.org/10.1017/S0950268823001206  PMID: 37503568 
  6. Graham FF, Harte D, Zhang J, Fyfe C, Baker MG. Increased incidence of legionellosis after improved diagnostic methods, New Zealand, 2000-2020. Emerg Infect Dis. 2023;29(6):1173-82.  https://doi.org/10.3201/eid2906.221598  PMID: 37209673 
  7. Pampaka D, Gómez-Barroso D, López-Perea N, Carmona R, Portero RC. Meteorological conditions and Legionnaires’ disease sporadic cases-a systematic review. Environ Res. 2022;214(Pt 4):114080.  https://doi.org/10.1016/j.envres.2022.114080  PMID: 35964674 
  8. Iera J, Cannone A, Fadda G, Urciuoli R, Giannitelli S, Sciurti A, et al. I risultati del sistema di sorveglianza nazionale della legionellosi coordinato dall’Istituto Superiore di Sanità, anno 2023. [Results from the national Legionnaires’ disease surveillance system in Italy: 2023 data]. Italian. Boll Epidemiol Naz.2024;5(3):29-38.
  9. Italian Ministry of Health. Linee guida per la prevenzione ed il controllo della legionellosi. [Guidelines for Legionnaire’s disease prevention and control]. Rome: Italian Ministry of Health; 2015. Italian. Available from: https://web.archive.org/web/20240301034202/https://www.salute.gov.it/portale/documentazione/p6_2_2_1.jsp?lingua=italiano&id=2362
  10. 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. Available from: data.europa.eu/eli/dec_impl/2018/945/oj
  11. World Health Organization (WHO). Legionella and the prevention of legionellosis. Geneva: WHO; 11 Apr 2007. Available from: https://iris.who.int/server/api/core/bitstreams/7db5c118-fbf4-4597-8e1b-7d01a3bbeac9/content
  12. Raffa M, Reder A, Marras GF, Mancini M, Scipione G, Santini M, et al. VHR-REA_IT Dataset: Very High Resolution dynamical downscaling of ERA5 reanalysis over Italy by COSMO-CLM. Data (Basel). 2021;6(8):88.  https://doi.org/10.3390/data6080088 
  13. World Metereological Organization (WMO). Guide to Instruments and Methods of Observation – Measurement of Meteorological Variables. Geneva: WMO; 2023. Available from: library.wmo.int/idurl/4/68695
  14. Italian Ministry of Health and Ministry of Economy and Finance. Conference of Italian Regions and autonomous Provinces. Linee guida recanti indicazioni ai laboratori con attività di diagnosi microbiologica e controllo ambientale della legionellosi. [Guidelines for laboratories performing microbiological diagnosis and environmental control of legionellosis]. Rome: Italian Ministry of Health and Ministry of Economy and Finance; 13 Jan 2005. Italian. Available from: https://www.gazzettaufficiale.it/eli/id/2005/02/05/05A00848/sg
  15. Madaniyazi L, Tobias A, Kim Y, Chung Y, Armstrong B, Hashizume M. Assessing seasonality and the role of its potential drivers in environmental epidemiology: a tutorial. Int J Epidemiol. 2022;51(5):1677-86.  https://doi.org/10.1093/ije/dyac115  PMID: 35639562 
  16. Gasparrini A. A tutorial on the case time series design for small-area analysis. BMC Med Res Methodol. 2022;22(1):129.  https://doi.org/10.1186/s12874-022-01612-x  PMID: 35501713 
  17. Egan JR, Hall IM, Lemon DJ, Leach S. Modeling Legionnaires’ disease outbreaks: estimating the timing of an aerosolized release using symptom-onset dates. Epidemiology. 2011;22(2):188-98.  https://doi.org/10.1097/EDE.0b013e31820937c6  PMID: 21242803 
  18. Halsby KD, Joseph CA, Lee JV, Wilkinson P. The relationship between meteorological variables and sporadic cases of Legionnaires’ disease in residents of England and Wales. Epidemiol Infect. 2014;142(11):2352-9.  https://doi.org/10.1017/S0950268813003294  PMID: 24406306 
  19. Ricketts KD, Charlett A, Gelb D, Lane C, Lee JV, Joseph CA. Weather patterns and Legionnaires’ disease: a meteorological study. Epidemiol Infect. 2009;137(7):1003-12.  https://doi.org/10.1017/S095026880800157X  PMID: 19017428 
  20. 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 
  21. 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 
  22. Gasparrini A, Armstrong B, Kenward MG. Distributed lag non-linear models. Stat Med. 2010;29(21):2224-34.  https://doi.org/10.1002/sim.3940  PMID: 20812303 
  23. Italian National Institute of Statistics (Istat). Popolazione residente e dinamica della popolazione - Anno 2023. [Resident population and population dynamics – 2023]. Rome: Istat. [Accessed: 20 Feb 2026]. Italian. Available from: https://www.istat.it/comunicato-stampa/popolazione-residente-e-dinamica-della-popolazione
  24. Cooley LA, Pondo T, Francois Watkins LK, Shah P, Schrag S, Active Bacterial Core Surveillance Program of the Emerging Infections Program Network. Population-based assessment of clinical risk factors for Legionnaires’ disease. Clin Infect Dis. 2020;70(11):2428-31.  https://doi.org/10.1093/cid/ciz771  PMID: 31617567 
  25. Samuelsson J, Payne Hallström L, Marrone G, Gomes Dias J. Legionnaires’ disease in the EU/EEA*: increasing trend from 2017 to 2019. Euro Surveill. 2023;28(11):2200114.  https://doi.org/10.2807/1560-7917.ES.2023.28.11.2200114  PMID: 36927719 
  26. Leung YH, Lam CK, Cheung YY, Chan CW, Chuang SK. Epidemiology of Legionnaires’ disease, Hong Kong, China, 2005-2015. Emerg Infect Dis. 2020;26(8):1695-702.  https://doi.org/10.3201/eid2608.191244  PMID: 32687025 
  27. Fisman DN, Lim S, Wellenius GA, Johnson C, Britz P, Gaskins M, et al. It’s not the heat, it’s the humidity: wet weather increases legionellosis risk in the greater Philadelphia metropolitan area. J Infect Dis. 2005;192(12):2066-73.  https://doi.org/10.1086/498248  PMID: 16288369 
  28. 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 
  29. Braeye T, Echahidi F, Meghraoui A, Laisnez V, Hens N. Short-term associations between Legionnaires’ disease incidence and meteorological variables in Belgium, 2011-2019. Epidemiol Infect. 2020;148:e150.  https://doi.org/10.1017/S0950268820000886  PMID: 32345387 
  30. Wade TJ, Herbert C. Weather conditions and legionellosis: a nationwide case-crossover study among Medicare recipients. Epidemiol Infect. 2024;152:e125.  https://doi.org/10.1017/S0950268824000979  PMID: 39417401 
  31. Cassell K, Warren JL, Heneghan C, Weinberger DM. Incorporating incubation period distributions to precisely estimate the association between rainfall and Legionella infection. J Infect Dis. 2025;231(6):1502-11.  https://doi.org/10.1093/infdis/jiae625  PMID: 39689015 
  32. Faccini M, Russo AG, Bonini M, Tunesi S, Murtas R, Sandrini M, et al. Large community-acquired Legionnaires’ disease outbreak caused by Legionella pneumophila serogroup 1, Italy, July to August 2018. Euro Surveill. 2020;25(20):1900523.  https://doi.org/10.2807/1560-7917.ES.2020.25.20.1900523  PMID: 32458793 
  33. Ohno A, Kato N, Sakamoto R, Kimura S, Yamaguchi K. Temperature-dependent parasitic relationship between Legionella pneumophila and a free-living amoeba (Acanthamoeba castellanii). Appl Environ Microbiol. 2008;74(14):4585-8.  https://doi.org/10.1128/AEM.00083-08  PMID: 18502936 
  34. Taylor M, Ross K, Bentham R. Legionella, protozoa, and biofilms: interactions within complex microbial systems. Microb Ecol. 2009;58(3):538-47.  https://doi.org/10.1007/s00248-009-9514-z  PMID: 19365668 
  35. Margot C, Rhoads W, Gabrielli M, Olive M, Hammes F. Dynamics of drinking water biofilm formation associated with Legionella spp. colonization. NPJ Biofilms Microbiomes. 2024;10(1):101.  https://doi.org/10.1038/s41522-024-00573-x  PMID: 39368992 
  36. van Heijnsbergen E, de Roda Husman AM, Lodder WJ, Bouwknegt M, Docters van Leeuwen AE, Bruin JP, et al. Viable Legionella pneumophila bacteria in natural soil and rainwater puddles. J Appl Microbiol. 2014;117(3):882-90.  https://doi.org/10.1111/jam.12559  PMID: 24888231 
  37. Hambleton P, Broster MG, Dennis PJ, Henstridge R, Fitzgeorge R, Conlan JW. Survival of virulent Legionella pneumophila in aerosols. J Hyg (Lond). 1983;90(3):451-60.  https://doi.org/10.1017/S0022172400029090  PMID: 6863914 
  38. Katz SM, Hammel JM. The effect of drying, heat, and pH on the survival of Legionella pneumophila. Ann Clin Lab Sci. 1987;17(3):150-6. PMID: 3606021 
  39. Mistry MN, Schneider R, Masselot P, Royé D, Armstrong B, Kyselý J, et al. Comparison of weather station and climate reanalysis data for modelling temperature-related mortality. Sci Rep. 2022;12(1):5178.  https://doi.org/10.1038/s41598-022-09049-4  PMID: 35338191 
  40. Rota MC, Cawthorne A, Bella A, Caporali MG, Filia A, D’Ancona F, et al. Capture-recapture estimation of underreporting of legionellosis cases to the National Legionellosis Register: Italy 2002. Epidemiol Infect. 2007;135(6):1030-6.  https://doi.org/10.1017/S0950268806007667  PMID: 17176499 
  41. Mercante JW, Winchell JM. Current and emerging Legionella diagnostics for laboratory and outbreak investigations. Clin Microbiol Rev. 2015;28(1):95-133.  https://doi.org/10.1128/CMR.00029-14  PMID: 25567224 
  42. Kowalczyk B, Petzold M, Kaczyński Z, Szuster-Ciesielska A, Luchowski R, Gruszecki WI, et al. Lipopolysaccharide of Legionella pneumophila serogroup 1 facilitates interaction with host cells. Int J Mol Sci. 2023;24(19):14602.  https://doi.org/10.3390/ijms241914602  PMID: 37834049 
  43. Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC). Risk analysis. Climate change in Italy. Lecce: CMCC; 2020. Available from: cmcc.it/wp-content/uploads/2020/09/en_EXECUTIVE_SUMMARY_CMCC_climate_RISK_in_ITALY.pdf
  44. Intergovernmental Panel on Climate Change (IPCC). Climate Change 2021 – The Physical Science Basis: Working Group I Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change – Technical Summary. In: Climate Change 2021 – The Physical Science Basis: Working Group I Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press; 2023. p. 35-144. Available from: https://www.cambridge.org/core/product/C7CCEAD271B10F328C6E50C03A0F4F02
  45. Sakamoto R. Legionnaire’s disease, weather and climate. Bull World Health Organ. 2015;93(6):435-6.  https://doi.org/10.2471/BLT.14.142299  PMID: 26240466 
  46. Ricci ML, Grottola A, Fregni Serpini G, Bella A, Rota MC, Frascaro F, et al. Improvement of Legionnaires’ disease diagnosis using real-time PCR assay: a retrospective analysis, Italy, 2010 to 2015. Euro Surveill. 2018;23(50):1800032.  https://doi.org/10.2807/1560-7917.ES.2018.23.50.1800032  PMID: 30563592 
  47. Rota M, Caporali M, Bella A, Scaturro M, Giannitelli S, Ricci M. I risultati del sistema di sorveglianza della legionellosi in Italia nel 2020 durante la pandemia di COVID-19. [Legionellosis in Italy and COVID-19 pandemic: results of the Italian National Surveillance System for legionellosis for the year 2020]. Italian. Boll Epidemiol Naz.2021;2(3):9-16.
  48. European Centre for Disease Prevention and Control (ECDC). Legionnaires’ disease - Annual Epidemiological Report for 2020. Stockholm: ECDC; 10 May 2022. Available from: ecdc.europa.eu/en/publications-data/legionnaires-disease-annual-epidemiological-report-2020
  49. Burlingame GA, Bartrand TA. Laying the groundwork for a Legionella pneumophila risk management program for public drinking water systems. J Water Health. 2024;22(12):2385-97.  https://doi.org/10.2166/wh.2024.476  PMID: 39733363 
  50. Eurostat. Revision of the European Standard Population: report of Eurostat’s task force. Luxembourg: Eurostat; 2013. Available from: https://ec.europa.eu/eurostat/documents/3859598/5926869/KS-RA-13-028-EN.PDF.pdf/e713fa79-1add-44e8-b23d-5e8fa09b3f8f?t=1414782757000
Seasonality and effects of climatic exposures on community-acquired Legionnaires’ disease incidence, Italy, 2005 to 2023
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Antonio+Sciurti&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Sciurti Antonio</a>, <a href="/search?value1=Jessica+Iera&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Iera Jessica</a>, <a href="/search?value1=Andrea+Cannone&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Cannone Andrea</a>, <a href="/search?value1=Alberto+Mateo-Urdiales&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Mateo-Urdiales Alberto</a>, <a href="/search?value1=Luigi+De+Angelis&option1=author&noRedirect=true" class="nonDisambigAuthorLink">De Angelis Luigi</a>, <a href="/search?value1=Valentina+Baccolini&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Baccolini Valentina</a>, <a href="/search?value1=Roberta+Urciuoli&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Urciuoli Roberta</a>, <a href="/search?value1=Stefania+Giannitelli&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Giannitelli Stefania</a>, <a href="/search?value1=Giulia+Fadda&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Fadda Giulia</a>, <a href="/search?value1=Benedetta+Bellini&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Bellini Benedetta</a>, <a href="/search?value1=Fabiola+Mancini&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Mancini Fabiola</a>, <a href="/search?value1=Maria+Scaturro&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Scaturro Maria</a>, <a href="/search?value1=Maria+Cristina+Rota&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Rota Maria Cristina</a>, <a href="/search?value1=Maria+Luisa+Ricci&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Ricci Maria Luisa</a>, <a href="/search?value1=Antonino+Bella&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Bella Antonino</a>, <a href="/search?value1=Patrizio+Pezzotti&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Pezzotti Patrizio</a></span>. Seasonality and effects of climatic exposures on community-acquired Legionnaires’ disease incidence, Italy, 2005 to 2023. <a href="/content/ecdc">Euro Surveill.</a> 2026;31(12):pii=2500712. <a href="https://doi.org/10.2807/1560-7917.ES.2026.31.12.2500712" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2026.31.12.2500712</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 11 Sept 2025;&nbsp;&nbsp; <span class="generated">Accepted</span>: 28 Nov 2025 </span> </p>
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