What legionella outbreaks has the UK seen?
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Key points
- An outbreak is two or more cases linked in time and place; most UK legionnaires' disease is sporadic single cases, not outbreaks.
- The worst UK outbreak was Barrow-in-Furness 2002: 7 deaths, around 180 ill, from a council-run cooling system.
- UKHSA recorded 472 legionellosis cases in England and Wales in 2024, with 13 deaths; the recent peak was 604 in 2023.
- Investigations pair patient exposure histories with water-system sampling and strain matching.
- Prosecuted outbreaks almost always trace back to missing basics: no assessment, no written scheme, no monitoring.
A legionnaires' disease outbreak is two or more cases linked in time and place to a common source. Most UK cases are not part of one: UKHSA recorded 472 legionellosis cases in England and Wales in 2024, and the largest category was sporadic, community-acquired infection. Outbreaks are the visible tip of a mostly invisible total.
This page does two things: it explains what an outbreak is and how one is investigated, and it lists the notable UK outbreaks with their documented figures, drawn from our enforcement tracker dataset and published surveillance. Every figure is cited to its source; where numbers differ between reports, we quote the source noted in the dataset.
The surveillance backdrop
UKHSA publishes legionellosis surveillance for England and Wales once a year. The latest release (published 20 November 2025) covers 2024:
| Year | Cases | Deaths | Case fatality rate |
|---|---|---|---|
| 2017 | 488 | 36 | 7.4% |
| 2018 | 554 | 36 | 6.5% |
| 2019 | 551 | 34 | 6.3% |
| 2020 | 338 | 36 | 10.7% |
| 2021 | 352 | 29 | 8.2% |
| 2022 | 413 | 29 | 7.0% |
| 2023 | 604 | 19 | 3.1% |
| 2024 | 472 | 13 | 2.8% |
Of the 2024 cases, 51.6% were classed as community-acquired, 43.8% were associated with travel abroad, and 4.5% were healthcare-associated. Cases concentrate in older age groups: nearly two thirds of 2024 cases were aged 60 or over. Scotland is reported separately: Public Health Scotland recorded 57 cases in 2024, 10.4 per million population. The full regional and exposure breakdown is on the Legionella Data Index, which notes honestly where UKHSA does not publish regional rates.
Notable UK outbreaks
The outbreaks below are the ones that shaped UK legionella control. Case details come from the sources cited against each case in our enforcement dataset.
Barrow-in-Furness, 2002: the worst on record
Seven people died and around 180 fell ill in August 2002. The source was a poorly maintained cooling system serving the air conditioning at the council-run Forum 28 arts centre. Barrow Borough Council was convicted of breaching section 3(1) of the Health and Safety at Work etc. Act 1974 and fined £125,000 plus £90,000 costs in July 2006; it was the first UK public body to face corporate manslaughter charges, dropped before the HSWA conviction (source: HSE account of the outbreak). Barrow is why water-based cooling plant is regulated so tightly: see air conditioning and legionella.
Stoke-on-Trent, 2012: the display hot tub
A heated spa pool displayed for sale for months at a JTF Wholesale warehouse store caused an outbreak in which 21 people fell ill and three died. The HSE considered corporate manslaughter before accepting a guilty plea; the company was fined £1 million in 2017 (source: ITV News report of the sentencing). It remains the defining case for why display spas must be filled, treated and maintained like operating ones: see hot tubs and spa pools.
Dundee, 2015: a Pontiac fever outbreak
Sixty-five people fell ill, 18 with confirmed Pontiac fever, from the leisure-club spa pool at the then-Landmark Hotel. The pool had not been fully drained, cleaned or disinfected for over two months and a failed chlorine injector let bacteria breed. Operator BDL Select Operations was fined £54,000 in 2016 (source: STV News archive). Notably, nobody died: Pontiac fever is the non-pneumonic form of legionellosis.
Basildon, 2006 to 2007: a hospital outbreak
A chronic legionella outbreak in the Basildon and Thurrock hospital water system infected seven patients; two died. Shower heads, hoses and thermostatic controls were not maintained. The Trust was fined £100,000 plus around £162,000 costs in 2013 (source: Nursing Times). Healthcare outbreaks also drove the Brighton and Sussex case (£50,000 fine in 2015 after 114 positive tests and 651 out-of-range temperature records went unactioned) and the Royal United Hospitals Bath case (£300,000 in 2018, over an annexe loop never temperature-checked).
Cooling-tower community outbreaks
Two manufacturing cases show how cooling towers expose the public, not just workers. At Riaar Plastics in West Bromwich, five people including members of the public contracted legionnaires' disease in 2020; the company was fined £50,000 in 2023. At Faltec in the North East, five people including a local resident were infected from recirculating cooling water; the fine in 2018 was £800,000. Earlier, Chromalloy (2015, £110,000) and Coilcolor (2015, £75,000) were prosecuted for tower management failures before anyone was confirmed ill.
How an outbreak is investigated
When two or more cases are linked, the pattern is consistent:
- Case finding and exposure histories. Public health teams interview every case about where they were in the roughly two weeks before illness, building a map of shared places.
- Environmental investigation. Suspect water systems at the shared locations are sampled and inspected, by local authority environmental health or the HSE depending on the premises.
- Control first, answers second. Cleaning, disinfection or shutdown of suspect equipment is imposed as soon as a plausible source is identified, without waiting for laboratory confirmation.
- Strain matching. Where legionella is found in a system, the strain is compared with the strain isolated from patients. A match is the strongest evidence of the source; without it, a premises may be prosecuted for the management failure rather than for causing the illness, as in the Royal United Hospitals Bath case.
Enforcement then follows the management record, not just the outcome: see legionella fines and prosecutions for how fines are set.
Read across the prosecuted outbreaks and the same sentence keeps appearing: no adequate risk assessment, no written scheme, no monitoring, no training. Outbreaks are rarely accidents of fate; they are unmanaged systems finally meeting their occupants.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
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What this means for duty holders
The duty under ACOP L8 does not wait for a case. Several of the largest fines in the dataset, G4S (£1.8 million, 2016) and Isher Hangers (suspended custodial sentences, 2020), involved no confirmed infection at all. The records you keep are what demonstrate control is real: a current risk assessment, a written scheme, monitoring logs and training records. If you are found to have managed the system properly, an investigation is an inspection; if not, it becomes evidence.
Sources
Surveillance figures: UKHSA, Legionellosis in residents of England and Wales: 2024 (published 20 November 2025); Public Health Scotland, Legionnaires' disease in Scotland surveillance report 2024 (published 26 August 2025). Outbreak and fine details: the primary sources cited per case in our enforcement dataset, including the HSE account of Barrow, ITV News (JTF), STV News (BDL), the Nursing Times (Basildon), IOSH Magazine (Riaar, Faltec, Bupa), and court and regulator reports linked in the enforcement tracker.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
What counts as a legionnaires' disease outbreak?
In UK public health practice, an outbreak is generally two or more cases linked in time and place to a common suspected source. A single case is investigated too, but as a sporadic case. Most legionnaires' disease in the UK is sporadic rather than part of an outbreak: of the 472 legionellosis cases in England and Wales in 2024, the largest exposure category was community-acquired infection (UKHSA surveillance).
What was the worst legionella outbreak in the UK?
The Barrow-in-Furness outbreak of August 2002: seven people died and around 180 fell ill, traced to a poorly maintained cooling system at the council-run Forum 28 arts centre. Barrow Borough Council was convicted under the Health and Safety at Work Act and fined £125,000 plus £90,000 costs in 2006 (source: HSE account of the outbreak). It remains the UK's deadliest recorded legionnaires' disease outbreak.
How many cases of legionnaires' disease are there in the UK each year?
UKHSA recorded 472 legionellosis cases in England and Wales in 2024, with 13 deaths (a case fatality rate of 2.8%). The recent peak was 604 cases in 2023; the annual series since 2017 has ranged between 338 and 604. Scotland, which UKHSA does not cover, recorded 57 cases in 2024, 10.4 per million population (Public Health Scotland). Figures are published annually, usually each November.
How is a legionella outbreak investigated?
Public health teams interview cases to map exposures in the incubation period, while environmental health or HSE inspectors sample suspected water systems. Where legionella is found, the strain from the system is compared with the strain from the patient; a match is the strongest evidence of the source. Control measures, cleaning, disinfection or shutting equipment down, are imposed as soon as a suspect source is identified, before the detective work finishes.
What usually causes legionella outbreaks?
The prosecuted UK outbreaks share a short list of failures: unmaintained cooling towers and evaporative condensers (Barrow 2002, Riaar Plastics 2020, Faltec), display or leisure spa pools (JTF Wholesale 2012, BDL Select 2016), and unmanaged hot and cold water systems in hospitals, care homes and hotels. In nearly every case the enforcement finding was not bad luck but the absence of a working risk assessment, written scheme, monitoring or training.
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