A total of 25 people are now suffering from the winter vomiting bug in Dublin's St Vincent's hospital.
The hospital said that ten wards had been shut and that 15 patients and 10 members of staff were being treated for the Norovirus.
To help stop the spread of the bug in the hospital, it has appealed to the public to only go to its emergency department if necessary, to avoid visiting patients unless necessary and to keep children away from the hospital for visits.
"We appreciate that Christmas is a time when people want to visit patients, so we are asking just that the level of visits be curtailed," a statement said.
