The Health Protection Agency (HPA) has launched an investigation into a cluster of cases of Legionnaires' disease in people who have been to Corfu.
The organisation said it is aware of nine cases of the disease in people, whose ages range from 39 to 79, who have travelled to different areas of the Greek island since August.
The HPA is 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 possible source or sources.
They said although cases all have a history of recent travel to Corfu, a UK source of infection cannot be ruled out.
As a precaution, it will investigate possible UK sources, as well as working with Greek authorities to look at possible sources in Corfu.
The HPA is advising people going on holiday to the island to be aware of signs and symptoms of Legionnaires'. The disease, caused by the legionella bacterium, 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 can start between two and 14 days after exposure to a source, often with an initial flu-like illness leading to pneumonia.
Legionnaires' disease is uncommon in the UK, but can lead to complications and can be fatal, the HPA said. Early antibiotic 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.