A patient in a hospital in Essex has contracted Legionnaire's disease.
Legionnaire's disease is a rare form of pneumonia
The rare form of pneumonia was confirmed a week ago, the Basildon and Thurrock NHS Trust said on Thursday.
Earlier this year the Trust was fined for failing to control a bug which can cause Legionnaire's disease, after the death of a patient in 2002.
At the time, the Trust carried out £300,000 of work to the hot water systems in the building, which can harbour the bacteria.
But following the diagnosis of this new case at Basildon Hospital, tests revealed the problem has returned.
Patients with suspected pneumonia are being tested for the bacteria, and work is being done to get rid of the contamination.
Alan Whittle, chief executive of the Trust, said: "It is not possible to eradicate the bacteria and we did, and have continued to do, everything that was
recommended to manage the risk.
"We are urgently re-examining all of our controls with experts from the Health Protection Agency and are awaiting further test results to determine what
other actions we need to take.
"In addition to the continuous measures we have been taking to manage the
water supply, we have carried out very high temperature pasteurisation to
eliminate the current contamination."