The restrictions on visitors to two Co Mayo hospitals are to continue until Wednesday at the earliest, say Western Health Board officials.
The two hospitals are believed to be infected by a highly contagious virus that has already infected up to 80 patients.
The Western Health Board is appealing to people wishing to visit patients or people who are not suffering from serious injuries to stay away from the two hospitals as they attempt to contain the virus.
The Health Board has named the two hospitals as Mayo General Hospital and The Sacred Heart Hospital in Castlebar but are insisting that the virus is not life-threatening.