Over 40 patients are being treated for the so-called winter vomiting bug at three hospitals in the west, mid-west and the southeast.
The latest outbreak of the gastro-intestinal illness has hit University College Hospital in Galway where 20 patients have been diagnosed as having the illness.
Two wards there are now closed to all further admissions.
The Western Health Board wants relatives and friends of patients to minimise their visits to the hospital and is asking people with symptoms of gastro-enteritis to visit their local GPs instead of the hospital's A&E department.
In the southeast, 16 patients at St Columba's Hospital in Thomastown, Co Kilkenny, have contracted the illness as have five patients at the Mid-West Regional Hospital in Limerick.
It is now three years since the first outbreak of the illness in the country was detected at the Galway hospital.
