Sixteen suspected cases of the winter vomiting bug have been reported at St. Patrick's Hospital in Waterford. The hospital has been closed to visitors and admissions following a request to the public from the hospital board.
Full infection control measures have been implemented to reduce the risk of the bug from spreading further.
Patients are being monitored and are comfortable at present and people who wish to contact the hospital in relation to patient queries should ring 051 848000.
St. Patrick's Hospital, which provides rehabilitation care, respite care and a long-stay residential hospital for older people, was closed for a period in 2002 after one patient showed symptoms of the virus.
The virus is a "self-limiting" bug which cannot be treated and must wear itself out. Healthy people can overcome the symptoms within 48 hours.