A probe has been launched amid fears patients at Beaumont Hospital could have been operated on using instruments contaminated with Creutzfeldt-Jakob disease (CJD).
The Northern Ireland Health and Safety Executive (HSE) has revealed it is checking records to see how many patients could be affected.
The investigation comes after a patient was diagnosed with the life-threatening condition.
The fatal brain disease can be passed on through contaminated surgical instruments and international guidelines say any equipment used on a patient with CJD must be put through a special highly-rigorous sterilisation procedure or destroyed. Normal sterilisation techniques can fail to properly get rid of the infection.
It is understood the operation concerning the infected patient happened two weeks before their diagnosis. Instruments were not isolated until after this time and were used on other patients.
Those patients will now be contacted and will have to be monitored indefinitely.
In a statement, the HSE said: "Beaumont Hospital is receiving advice from the Irish Panel on TSE (CJD) and from world experts in the UK, who have dealt with similar cases in the UK and worldwide. "This group is assessing the circumstances of this case to determine what, if any, risk may exist for other patients."
A spokesperson for Beaumont Hospital added: "The primary concern is for patients and their care.
"Until the necessary risk assessment is completed and the necessary contact made with patients, the hospital is not in a position to discuss the issues under review.
"While the number of patients potentially affected is low and confined to one area of surgery, Beaumont will have a helpline open from 8am to respond to concerned patients."