There are now more than 100 cases of the winter vomiting bug at St Vincent's Hospital in Dublin.
There have been 40 new cases of the bug at the hospital in the last 12 hours, bringing the total affected to 76 patients and 45 staff.
The chief executive of the hospital, Nicky Jermyn, today described the situation at the hospital as serious.
Fifteen wards at the hospital are closed to new admissions as a result of the outbreak.
Hospital management says if the situation is not brought under control up to 100 procedures and operations for day patients could be cancelled next week.
A further 20 operations for overnight patients could also be postponed.
A spokesman for the hospital said it had placed additional pressures on services and that hospital management and medical staff were monitoring the situation closely.
The Eastern Regional Health Authority has stated that there are only a few cases of the bug in other Dublin hospitals.
ERHA has also repeated its appeal to people who feel they may have the winter vomiting bug to stay away from hospitals and A&E units.
Meanwhile, Beaumont Hospital has confirmed that it has eight cases of the bug.
However, the hospital says the situation is not serious and no wards have been closed or operations cancelled.
