The Irish Nurses Organisation has blamed overcrowding at St Vincent's Hospital in Dublin for contributing to the spread of the winter vomiting bug.
There are now 160 cases of the winter vomiting bug at the hospital.
A spokesman for the hospital said today that 95 patients and 65 staff had contracted the illness. That represents an increase of 18 patient and 22 staff cases since yesterday.
He added that another 45 patients are showing symptoms of the virus.
14 wards in the hospital remain closed to new admissions as a result of the outbreak.