Tallaght Hospital say they are taking all appropriate precautions as they treat patients who have been infected with a potentially lethal super bug known as CRE.
To prevent the bug spreading the hospital has closed two wards.
The outbreak was first confirmed last month leading to the closing of the Fogarty and Crampton wards.
A third ward may now also have to be closed.
It is undergoing contact screening as part of the urgent drive by the hospital to contain the spread.
CRE, short for carbapenem resistant enterobacteria, is generally not a risk to healthy people but poses a serious danger to patients whose immune systems are low.
Patients who are using catheters and ventilators or are taking antibiotics are the highest risk of becoming infected by the bug which is passed on by touch.
There are only a few antibiotics which can kill off the infection.
The paediatric emergency department and adult emergency department are separate units and neither have been associated with this outbreak.
The hospital say patients should continue to use both emergency units as normal.