Up to 20 people who underwent surgery with equipment used on patients with Creutzfeldt-Jakob Disease (CJD) are being contacted to warn them they need to be tested.
Health chiefs revealed between 10 and 20 people will be notified after the scare following treatment at Dublin's Beaumont Hospital.
The Health Service Executive (HSE) confirmed on Thursday that assessments are under way to see if any other patients have been put at risk of contracting the fatal degenerative brain disorder at the facility.
Medical experts have been checking records to see how many people have been operated on in recent weeks with instruments which had been used on the affected patient.
Dr Kevin Kelleher, the HSE's assistant national director of health protection, said up to 20 people are at higher risk of the disease following operations. The average rate of prevalence of CJD in Ireland is about one in a million people a year.
Patients being contacted by the HSE will be told they will need to be monitored over the long term with the possibility that they will undergo medical examinations for the rest of their lives.
The HSE said hospital managers are receiving advice from the UK, where medics have dealt with similar cases.
"This group is assessing the circumstances of this case to determine what, if any, risk may exist for other patients," she said. "Further information will be available once this group has completed its assessment. When a case of CJD is diagnosed a review is undertaken to ensure that any precautions, if needed, are taken, in line with the national and international guidance."
CJD is a rare illness and one of a group of diseases called prion diseases, which affect humans and animals, and can be spread to doctors and other patients through medical instruments if they are not put through a rigorous sterilisation procedure or destroyed.
Taoiseach Enda Kenny said he recognised it must be a difficult time for the patient who has been diagnosed with CJD and for their family. He said an expert panel had been set up to investigate the risks posed to those who underwent surgery with the affected equipment in a process he expects to be "absolutely thorough". "I hope that the expert panel set up will follow through on the process and will be able to come through with full information for anybody who might have come into contact," Mr Kenny said. "In respect to the risk, which I understand to be very low, it may be necessary to have regular assessments of those people throughout their lives."