The Health Protection Agency is investigating several cases of Legionnaires' disease in people who have been to Corfu.
The organisation said it was aware of nine cases of the disease in people aged 39 to 79 who had travelled to different areas of the island since August.
The agency is now working with colleagues in the UK, the European Centre for Disease Prevention and Control (ECDC), and Greek public health authorities to try to find the source.
They said that although the cases had all recently travelled to Corfu, a UK source of infection could not be ruled out.
The HPA is now advising people who are going to the island to be aware of the symptoms of the disease.
Caused by the legionella bacterium, Legionnaires' disease can lead to severe pneumonia. It can survive in water, and may be spread through exposure to water droplets from cooling systems, shower heads and taps, but cannot be spread from person to person.
Symptoms start between two and 14 days after exposure, often with an initial flu-like illness leading to pneumonia.
The disease is uncommon in the UK but can lead to complications and can be fatal, so early treatment is important.
Professor Nick Phin, head of the HPA's Legionnaires' department, said: "We are concerned that UK residents travelling to Corfu should be aware of this potential risk, however we are not suggesting that people change their holiday plans.
"Legionnaires' disease is very rare and cannot be spread from person to person so the risk is low.
"We are continuing our investigations so that we can provide the best advice for travellers and minimise the risk of further cases.
"Sometimes a source for the infection is never found, because the bacteria can live in a very wide variety of types of water supply."
The HPA is also briefing GPs asking them to be alert to people returning from Corfu suffering from relevant symptoms.
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