An unexpected increase in cases of Legionnaires' disease in parts of north-west and south-west London is being investigated by The UK Health Security Agency (UKHSA).
Specialists are trying to find out if the cases are linked and to establish the possible source of the disease.
Experts are looking at each case of the disease to have broken out this year, interviewing patients or their families to retrace their steps to find out if there is a common link, the UKHSA said.
The disease - a severe form of pneumonia that usually requires hospital treatment- is typically caught by breathing in droplets of water containing the legionella bacteria.
It is usually picked up from sources such as air conditioning systems, showers and taps that are not properly designed, installed or maintained.
The majority of cases are reported as single, isolated cases, but outbreaks can occur, according to the UKHSA.
It is routinely treated with antibiotics and is not easily passed from person to person.
The agency said around 300 cases were reported annually in England and Wales.
'Retracing steps'
Dr Janice Lo, consultant in health protection for London at the UKHSA, said: "At this stage, a common source has not yet been confirmed, but we are undertaking further investigations, with partners, that will provide us with more information.
"Legionella bacteria is widely distributed in the environment and can multiply in large water systems within buildings.
"It is important that water systems are properly maintained with regular testing and treatment to ensure that bacteria do not multiply and cause a risk to health."
Patients and their families are being interviewed to retrace their steps and this information is being cross-referenced for potential infection sources.
The managers of cooling towers and large water systems within the affected areas have been instructed to urgently treat their system with high doses of chlorine to kill any potential contamination, the UKHSA added.
Signs and symptoms of Legionnaires' disease include a flu-like illness with muscle aches, tiredness, headaches, dry cough and fever, and people with these symptoms should call NHS 111 or their GP for medical advice.
Listen to the best of BBC Radio London on Sounds and follow BBC London on Facebook, X and Instagram. Send your story ideas to hello.bbclondon@bbc.co.uk
(Feed generated with FetchRSS)