Visiting restrictions are in place at hospitals in Sligo, Letterkenny, Galway and Limerick following outbreaks of the winter vomiting bug.
A ban on visiting remains in place at the Mid-Western Regional Hospital in Limerick in an attempt to curb an outbreak of the bug.
Visitors to wards are prohibited, with the exception of agreed visits to critically ill patients.
Parents are also being advised to keep children away from all areas of the hospital.
People have been advised that they should only attend the Emergency Department if there is a genuine emergency.
Visiting restrictions have also been imposed at Sligo General Hospital.
Members of the public have been asked to visit only in essential or exceptional circumstances.
Immediate relatives are asked to visit only during the designated visiting times, 2pm-4pm and 6.30pm-8.30pm.
A statement says that children should not be brought in to visit.
Restrictions are also in place in one ward at Cavan General Hospital.