The UK Health Security Agency (UKHSA) has released its 2025 annual report on legionellosis in England and Wales, detailing a significant shift in case numbers following recent record highs. The data, published on 16 September 2026, examines the epidemiology of the disease through the National Enhanced Legionnaires’ Disease Surveillance Scheme (NELSS).
In 2024, the reporting period immediately preceding the latest analysis, there were 472 confirmed cases of legionellosis. This represents a 22% decrease compared to 2023, which saw a record-breaking 604 cases. Despite the drop in overall numbers, health officials recorded 13 deaths among confirmed cases in 2024, resulting in a case fatality rate of 2.8%.
The report highlights that Legionnaires’ disease remains a “notifiable disease,” meaning medical professionals are legally required to report suspected cases to local health protection teams.
Who is most at risk?
Exposure routes for the bacteria were split between three main categories:
- Community-acquired: 51.6% of cases.
- Travel-associated: 43.8% of cases.
- Healthcare-associated: 4.5% of cases.
The analysis also examined the long-term impact of the COVID-19 pandemic on the spread of the disease. Epidemiology was significantly disrupted during lockdown periods, and the 2023-2024 data indicates a rebound effect as travel and building occupancy returned to pre-pandemic levels before stabilizing in the most recent counts.
Preventing Legionella growth
Legionnaires’ disease is a severe form of pneumonia caused by inhaling small droplets of water containing Legionella bacteria. These bacteria multiply in water systems where temperatures are maintained between 20°C and 45°C, particularly in stagnant systems.
Common household and commercial risks include:
- Hot tubs, spa pools, and whirlpool baths.
- Cooling towers and evaporative condensers.
- Hot and cold water systems in large buildings like hotels or hospitals.
- Stagnant water in pipes or showerheads that are infrequently used.
Official health advice emphasises that proper maintenance of water systems is critical to preventing outbreaks. This includes ensuring water is stored at temperatures outside the 20-45°C danger zone and that systems are regularly cleaned and disinfected.
The national report follows a specific investigation into a cluster of cases in North West and South West London during March and April 2026. That cluster involved eight confirmed cases which were linked through genetic matching of the bacterial sequence, highlighting the ongoing importance of rapid surveillance and environmental testing to prevent wider community spread.