Where the cooling water drifts: an outbreak of Legionella pneumophila serogroup 1 in the central business district of Sydney, December 2023 – January 2024

Authors

  • Ms Eunice Stiboy National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia; South Eastern Sydney Local Health District, Randwick, New South Wales, Australia
  • Ms Misha Klingstrom South Eastern Sydney Local Health District, Randwick, New South Wales, Australia
  • Dr Karen Chee South Eastern Sydney Local Health District, Randwick, New South Wales, Australia
  • Prof. Mark J Ferson South Eastern Sydney Local Health District, Randwick, New South Wales, Australia; School of Population Health, UNSW Medicine, University of New South Wales, Sydney, Australia
  • Ms Sandra Chaverot South Eastern Sydney Local Health District, Randwick, New South Wales, Australia
  • Mr Brian Huang South Eastern Sydney Local Health District, Randwick, New South Wales, Australia
  • Mr Toby Hannan South Eastern Sydney Local Health District, Randwick, New South Wales, Australia
  • Mr Philip Pershen South Eastern Sydney Local Health District, Randwick, New South Wales, Australia
  • Dr Kirsty Hope Health Protection NSW, St Leonards, Australia
  • Ms Zoe Baldwin Health Protection NSW, St Leonards, Australia
  • Mr Geoffrey Prendergast Health Protection NSW, St Leonards, Australia
  • Ms Kristy McCreadie Health Protection NSW, St Leonards, Australia
  • Ms Anita Smojver City of Sydney, New South Wales, Australia
  • Dr Catherine Pitman NSW Health Pathology, Public Health Pathology, Sydney, Australia
  • Ms Anna Smith NSW Health Pathology, Forensic and Analytical Science Service, Lidcombe, Australia
  • Ms Keira Glasgow Health Protection NSW, St Leonards, Australia
  • Prof. Vitali Sintchenko NSW Health Pathology, Westmead, Australia; Centre for Infectious Diseases and Microbiology – Public Health, The University of Sydney, New South Wales, Australia
  • Dr Geraldine Sullivan NSW Health Pathology, Westmead, Australia
  • Dr Qinning Wang NSW Health Pathology, Westmead, Australia
  • Dr Amy E Parry National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia
  • Dr Jeremy McAnulty Health Protection NSW, St Leonards, Australia
  • Dr Vicky Sheppeard South Eastern Sydney Local Health District, Randwick, Australia; School of Public Health, University of Sydney, Australia
  • Dr Anthea L Katelaris South Eastern Sydney Local Health District, Randwick Hospitals Campus, Hut 'U' Easy Street, Locked Bag 88, Randwick, NSW 2031

DOI:

https://doi.org/10.33321/cdi.2025.49.063

Keywords:

legionnaires disease, legionellosis, Legionella pneumophila, Legionella outbreak

Abstract

Background

Legionnaires’ disease causes severe pneumonia. Outbreaks are infrequent in Australia, with cooling water systems (CWS) regulated to reduce risk. In summer 2024, a Legionella pneumophila serogroup 1 (Lp1) outbreak was detected in visitors to the Sydney central business district (CBD). We investigated to identify cases and to control the source.

Methods

Case-patients were detected through routine laboratory notifications and classified as per surveillance case definitions. Case-patients were interviewed to determine symptoms, and environmental exposures 2–10 days prior to symptom onset. We mapped exposures sites and walking routes to identify areas for investigation. CWS in shared exposure areas were inspected and tested for Legionella. Historical results from routine CWS testing were reviewed. Genomic sequencing was performed on environmental and patient isolates. Clinician and public alerts were issued, and CBD building managers were reminded to maintain CWS.

Results

The investigation identified 15 legionellosis case-patients: two had Lp1 positive sputum cultures, 14 were hospitalised, and six required intensive care. All case-patients visited the CBD during the period 12–26 December 2023. Between 3–12 January 2024, testing was performed on 166 CWS across 118 CBD sites, and on three water fountains. Lp1 was cultured from one CWS. Genomic sequencing from five environmental and two clinical isolates showed a probable link. The positive CWS was decontaminated but continued to have Lp1 detected, possibly due to ongoing dust contamination, necessitating additional maintenance.

Weeks later, a case-patient diagnosed in Europe, who had visited key exposure locations in the CBD during 21–23 December 2023, was epidemiologically linked to the outbreak; this took the total number of case-patients to 16.

Conclusions

Our investigation indicated that a contaminated CWS may have been the source of this outbreak, with contamination potentially precipitated by nearby construction. This emphasises the importance of strengthening Australian CWS regulations to reduce Lp1 outbreak risk, and of timely reporting under International Health Regulations to identify additional outbreak cases.

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References

Australian Government Department of Health, Disability and Ageing, Communicable Diseases Network Australia (CDNA). Legionellosis – CDNA National Guidelines for Public Health Units. Canberra: Australian Government Department of Health, Disability and Ageing; 21 March 2017. Available from: https://www.health.gov.au/sites/default/files/2025-03/legionellosis-cdna-national-guidelines-for-public-health-units_0.pdf.

New South Wales State Government Department of Health (NSW Health). Legionnaires' disease control guideline. [Webpage.] Sydney: NSW Health; 9 May 2023. Available from: https://www.health.nsw.gov.au/Infectious/controlguideline/Pages/legion.aspx.

enHealth. Guidelines for Legionella control in the operation and maintenance of water distribution systems in health and aged care facilities. Canberra: Australian Government Department of Health, Disability and Ageing; 2015. Available from: https://www.health.gov.au/sites/default/files/documents/2022/07/enhealth-guidance-guidelines-for-legionella-control.pdf.

New South Wales State Government Register of Legislation. Public Health Regulation 2022. [Legislation.] Sydney: New South Wales State Government; 2023. Available from: https://legislation.nsw.gov.au/view/html/inforce/current/sl-2022-0502.

Victoria State Government Department of Health (Victoria Health). Legionella risks – identification and analysis: Section 6. [Webpage.] Melbourne: Victoria Health; 30 December 2024. Available from: https://www.health.vic.gov.au/water/legionella-risks-identification-and-analysis-section-6.

Capon A, Cains T, Draper J, Sintchenko V, Ferson M, Sheppeard V. Investigation of a legionellosis outbreak in Sydney CBD – a brief report. Aust N Z J Public Health. 2023;47(2):100018. doi: https://doi.org/10.1016/j.anzjph.2023.100018.

Quinn E, Johnstone T, Najjar Z, Cains T, Tan G, Huhtinen E et al. Lessons learned from implementing an incident command system during a local multiagency response to a Legionnaires’ disease cluster in Sydney, NSW. Disaster Med Public Health Prep. 2018;12(4):539–42. doi: https://doi.org/10.1017/dmp.2017.102.

Griffiths E, Gilmour R, Carlin M, Adamson S, Timms V, Chen S et al. Summary: Public Health investigation into the Legionella outbreaks in Sydney CBD: March and May 2016. Sydney: NSW Health; 4 November 2016. Available from: https://www.health.nsw.gov.au/Infectious/Publications/legionella-cbd-report.pdf.

NSW Health. Proposed changes to the regulation of water-cooling systems toprevent Legionnaires’ disease in NSW: Consultation Discussion Paper. Sydney: NSW Health; December 2016. Available from: https://www.health.nsw.gov.au/Infectious/Documents/legionnaires-disease-discussion-paper.pdf.

New South Wales State Government Register of Legislation. Public Health Act 2010 No 127. [Legislation.] Sydney: New South Wales State Government; 2023. Available from: https://legislation.nsw.gov.au/view/html/inforce/current/act-2010-127.

NSW Health. NSW Guidelines for Legionella Control in Cooling Water Systems. Sydney: NSW Health; 10 August 2018. Available from: https://www.health.nsw.gov.au/environment/legionellacontrol/Pages/guidelines-legionella-control.aspx.

Cambon J, Hernangómez D, Belanger C, Possenriede D. tidygeocoder: an R package for geocoding. J Open Source Softw. 2021;6(65):3544. doi: https://doi.org/10.21105/joss.03544.

QGIS Development Team. QGIS Resource Hub. [Software resource.] QGIS; 2024. Available from: https://qgis.org/resources/hub/.

Timms VJ, Rockett R, Bachmann NL, Martinez E, Wang Q, Chen SC et al. Genome sequencing links persistent outbreak of legionellosis in Sydney (New South Wales, Australia) to an emerging clone of Legionella pneumophila sequence type 211. Appl Environ Microbiol. 2018;84(5):e02020-17. doi: https://doi.org/10.1128/AEM.02020-17.

Sim E. DNA extraction for long-read sequencing of bacteria. Berkeley, California: Springer Nature, protocols.io; 3 November 2022. doi: https://doi.org/10.17504/protocols.io.4r3l2ox24v1y/v1.

Timms VJ, Sim E, Pey K, Sintchenko V. Can genomics and meteorology predict outbreaks of legionellosis in urban settings? Appl Environ Microbiol. 2024;90(8):e0065824. doi: https://doi.org/10.1128/aem.00658-24.

Seemann T, Gonçalves da Silva A, Buultjens A, Kwong J. Legsta. [Software.] GitHub repository; 26 February 2020. Available from: https://github.com/tseemann/legsta.

Seemann T, Wirth W, Chaudhuri R, Maguire F, Monzón S, Gonçalves da Silva A et al. Snippy. [Software.] GitHub repository; 9 March 2020. Available from: https://github.com/tseemann/snippy.

Gaia V, Fry NK, Afshar B, Lück PC, Meugnier H, Etienne J et al. Consensus sequence-based scheme for epidemiological typing of clinical and environmental isolates of Legionella pneumophila. J Clin Microbiol. 2005;43(5):2047–52. doi: https://doi.org/10.1128/JCM.43.5.2047-2052.2005.

Nguyen LT, Schmidt HA, von Haeseler A, Minh BQ. IQ-TREE: a fast and effective stochastic algorithm for estimating maximum-likelihood phylogenies. Mol Biol Evol. 2015;32(1):268–74. doi: https://doi.org/10.1093/molbev/msu300.

Yu G, Smith DK, Zhu H, Guan Y, Lam TTY. ggtree: an r package for visualization and annotation of phylogenetic trees with their covariates and other associated data. Methods Ecol Evol. 2017;8(1):28–36. doi: https://doi.org/10.1111/2041-210X.12628.

Raphael BH, Baker DJ, Nazarian E, Lapierre P, Bopp D, Kozak-Muiznieks NA et al. Genomic resolution of outbreak-associated Legionella pneumophila serogroup 1 isolates from New York State. Appl Environ Microbiol. 2016;82(12):3582–90. doi: https://doi.org/10.1128/AEM.00362-16.

von Baum H, Ewig S, Marre R, Suttorp N, Gonschior S, Welte T et al. Community-acquired Legionella pneumonia: new insights from the German competence network for community acquired pneumonia. Clin Infect Dis. 2008;46(9):1356–64. doi: https://doi.org/10.1086/586741.

European Centre for Disease Prevention and Control (ECDC). Legionnaires’ Disease Annual Epidemiological Report for 2021. Solna: ECDC; June 2023. Available from: https://www.ecdc.europa.eu/sites/default/files/documents/legionnaires-disease-annual-epidemiological-report-2021.pdf.

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. doi: https://doi.org/10.15585/mmwr.mm6522e1.

Mermel LA, Josephson SL, Giorgio CH, Dempsey J, Parenteau S. Association of Legionnaires' disease with construction: contamination of potable water? Infect Control Hosp Epidemiol. 1995;16(2):76–81. doi: https://doi.org/10.1086/647060.

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(4):114080. doi: https://doi.org/10.1016/j.envres.2022.114080.

Cains T, Shalak H, Timms VJ, Kiss A, Smith A, Sintchenko V et al. Legionella pneumophila serogroup 1 infection associated with the use of an apartment building spa pool. Commun Dis Intell (2018). 2022;46. doi: https://doi.org/10.33321/cdi.2022.46.82.

Australian Government Bureau of Meteorology (BoM). Daily maximum temperature: Sydney (Observatory Hill). Canberra: BoM; 2023. Available from: http://www.bom.gov.au/tmp/cdio/IDCJAC0010_066214_2023.pdf.

BoM. Sydney, New South Wales: December 2023 Daily Weather Observations. [Webpage.] Canberra: BoM; 2024. Available from: http://www.bom.gov.au/climate/dwo/202312/html/IDCJDW2124.202312.shtml.

Fischer FB, Saucy A, Vienneau D, Hattendorf J, Fanderl J, de Hoogh K et al. Impacts of weather and air pollution on Legionnaires’ disease in Switzerland: a national case-crossover study. Environ Res. 2023;233:116327. doi: https://doi.org/10.1016/j.envres.2023.116327.

Brown J, Hort K, Bouwman R, Capon A, Bansal N, Goldthorpe I et al. Investigation and control of a cluster of cases of Legionnaires disease in western Sydney. Commun Dis Intell Q Rep. 2001;25(2):63–6. doi: https://doi.org/10.33321/cdi.2001.25.13.

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Published

17/12/25

How to Cite

Stiboy, Eunice, Misha Klingstrom, Karen Chee, Mark Ferson, Sandra Chaverot, Brian Huang, Toby Hannan, et al. 2025. “Where the Cooling Water Drifts: An Outbreak of Legionella Pneumophila Serogroup 1 in the Central Business District of Sydney, December 2023 – January 2024”. Communicable Diseases Intelligence 49 (December). https://doi.org/10.33321/cdi.2025.49.063.

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Vol. 49 (2025)

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Original article

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