Visiting restrictions have been introduced at the Regional Hospital in Limerick to try to stem the spread of the "winter vomiting bug" after three cases were found.
Only family members are recommended to visit patients in the hospital at the moment, although the hospital management added there is no cause for alarm. Two children affected have already been discharged.
Today’s announcement follows other outbreaks around the country. More than 50 people in the Midland Regional Hospital in Mullingar were reported to have contracted the infection.
Outbreaks were reported in the Eastern Regional Health Authority (ERHA) and at Cavan General and Roscommon County Hospitals.
The virus is believed to have originated in Northern Ireland in December. Since then, hundreds of cases have been reported in Britain, including more than 200 at Glasgow's Victoria Infirmary Hospital last month.