Everything possible is being done to establish the cause of this outbreak and identify any patients affected

Dr Mark Wilcox

He added that a potential source has been identified and measures are being taken to rectify the problem.

An investigation is also underway and involves the hospital trust, health authority and the Health and Safety Executive.

"The trust is taking steps to check the health of patients who have been in the ward affected during this period," said the hospital spokesman.

"GPs and medical and ward staff have been alerted."

Risk of infection

The disease, which caused flu-like symptoms, is acquired by droplet inhalation through sources such as cooling towers, air conditioning systems and shower aerosols.

Person to person spread does not occur.

There are usually around 200 cases a year in the UK, of which up to 40 are fatal.

Dr Mark Wilcox, lead infection control doctor at the hospital, said: "Everything possible is being done to establish the cause of this outbreak and identify any patients affected.

"I would stress that the risk of further cases is very small and those people likely to be at risk are already being contacted."

A special helpline has been set up by NHS Direct for concerned members of the public on 01924 889 879.