Visitors have been banned from South Tipperary General Hospital, Mallow General Hospital, University Hospital Cork and University Hospital Limerick.
The facilities have come to the decision as they manage high volumes of patients with flu.
Management at all three hospitals are appealing to both adults and children who are experiencing any signs or symptoms of influenza to contact their local health provider in the first instance prior to attending the Emergency Department.
They are reminding the public that it is not too late to get the flu vaccine.
