The hospital trust has a 'no stars' rating

The man died three weeks ago after contracting the lethal bug at the city's Royal United Hospital (RUH).

But health bosses only released the details after the news was leaked to local media.

The disease, which is caused by water-borne bacteria, is thought to have spread from a contaminated shower head at the hospital.

The hospital trust, which has a 'no stars' rating in the NHS's league tables, said the case was an isolated one.

Legionnaires' is in the atmosphere all the time and is not specific to hospitals Mark Davies RUH chief executive

The RUH has since moved 12 high-risk cancer patients from a specialist ward after the bacteria was traced to a shower head in a nearby private room.

Two more patients with compromised immune systems on the William Budd Oncology Ward have been moved to hospitals in Bristol.

Legionnaires' disease, also known as legionellosis, is a rare form of pneumonia that contaminates water supplies and is fatal in 5-15% of cases.

RUH chief executive Mark Davies confirmed on Tuesday that a post-mortem examination on the man, who died on 13 February, revealed he had traces of the bug.

The patient, who has not been identified at the request of the family, contracted a strain of the bacteria typically found in people with compromised immune systems, such as those suffering from cancer.

Further tests

A statement from the hospital said: "Investigations traced a potential source of the infection to a shower head in the hospital ward where the patient was being treated."

Tests are still being carried out to determine whether the strain of legionella found in the shower is the same as that identified in the patient.

Mr Davies added: "We cannot raise the alarm about the disease when we don't know what the starting point is.

"Legionnaires' is in the atmosphere all the time and is not specific to hospitals. We had to find out its source before we could release information."

He said the hospital had been in constant contact with the patient's relatives throughout that time.

"We have expressed our sincere condolences and they were the first to know when it happened.

"Immediately we knew the post-mortem examination revealed legionella, although at that stage we did not know where it came from, we informed the Heath Protection Agency, the Health and Safety Executive and Bath and North East Somerset Council's environmental health department."

The ward will remain closed until the Health Protection Agency, which tackles outbreaks of infectious diseases, gives the go-ahead for it to be re-opened and further tests are completed.