A senior doctor at Beaumont Hospital has told colleagues he is "very concerned" after test results showed strains of a potentially deadly bacteria were present in several wards for "high-risk" patients.
The bacteria legionella, which can cause Legionnaires' disease, has been found in 18 of 33 water samples tested by the hospital last month.
In an email circulated to staff at Beaumont, the hospital's consultant microbiologist Professor Hilary Humphreys said the findings are "unacceptable".
The samples were taken from various areas within the hospital in June as part of regular weekly testing and assessed for the bacteria.
More than half of the samples contained the bacteria, while in eight cases the counts were above 1,000 per litre.
In the UK, guidelines issued last year said that in findings over 1,000 per litre, a risk assessment should be carried out.
It is understood no patients have fallen ill due to the bacteria, of which there are more than 40 strains. Positive samples included those taken from an oncology ward and in the high dependency unit.
Professor Humphreys said: "As I have stated before, I remain very concerned about these results."
He added that he understands the problems with legionella in the water system are on the HSE risk register
"However, is the HSE aware of the frequency of positive samples and the high count in high risk areas? Do they have any concerns with the real risk of hospital-acquired cases, or even the occurrence of an outbreak?"
A spokesperson for the hospital last night said: "We are fully compliant with the national guidelines and standards regarding monitoring, testing and controlling of legionella at Beaumont Hospital."
Under the standards, when the bacteria is found the area is disinfected and retested for the presence of legionella.
Legionnaire's disease is contracted by inhaling aerosols contaminated with bacteria. Most at risk are those over 40, smokers, alcoholics and those with low immune systems.
Irish Patients Association chief Stephen McMahon said the issue was "very serious" and that the planned introduction of a new copper water system should be done "as soon as possible".