Over 40 cases of the winter vomiting bug have been reported in the past three weeks at St John's Hospital in Sligo, the Health Service Executive confirmed today.
Patients and staff members were struck by the virus at the 190-bed hospital which caters mainly for elderly patients and those in need of rehabilitation.
Hospital chiefs have cracked down on visitors in an attempt to control the bug.
Members of the public have been asked to restrict their visiting times to the hospital in an attempt to control the spread of the virus. Visitors have also been requested not to move around the hospital.