HPR volume 20 issue 3: news (24 and 27 March, and 2 April 2026)

Updated 2 April 2026

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Outbreak of Legionnaires’ Disease, London

The UK Health Security Agency (UKHSA), alongside several London Local Authorities (LA) and the Health and Safety Executive (HSE), are continuing to investigate an outbreak of Legionnaires’ Disease in London.

The reported number of cases is atypical for this point in the year. Up to 23 March 2026, 8 confirmed cases had been identified with the same sequence type; all residing in, working in, or having visited North West (NW) or South West (SW) London.

A further 13 cases were under investigation to determine if they were part of the outbreak at that time.

An incident management team (IMT), with representation from all key stakeholders, has been coordinating the investigation and public health actions. The IMT agreed a case definition covering NW and SW London, which remains under review and may be updated as new information becomes available.

Epidemiological, microbiological, and environmental investigations are ongoing to determine whether there are any common links and to identify any potential common sources. No common exposure locations have been identified through case interviews.

UKHSA is continuing to work closely with LAs, Environmental Health teams, and the HSE to trace the movements of affected individuals and identify any potential environmental water sources for public health management.

Because cooling towers are often linked to Legionnaires’ Disease outbreaks, immediate control measures were implemented, including site visits, system inspections, water sampling, and precautionary shock‑dosing of cooling towers where appropriate.

Information was also shared with clinicians and hospital microbiologists, nationwide, to support active case finding, clarify notification requirements, and provide information on diagnostic sampling in line with local and national guidance.

Further information

Legionnaires’ disease: guidance, data and analysis

Respiratory and Vaccine Preventable Bacterial Reference Unit (RVPBRU, part of UKHSA’s Bacteriology Reference Department) provides reference laboratory services for a number of bacteria causing respiratory, systemic and vaccine preventable bacterial infections.