Up to 20 people who underwent surgery at Beaumont Hospital could be at risk of contracting CJD.
An investigation is underway at the hospital after a patient who was operated on was diagnosed with the degenerative brain condition two weeks later.
The HSE is to make contact with all those placed at risk.
CJD can be passed on on by contaminated instruments that have not been subjected to special sterilisation techniques.
The condition is is a degenerative nurological disorder which is incurable and invariably fatal.
The HSE says its now checking medical records to determine how many other patients were operated on using the same instruments.
Once identified they will have to be medically monitored for teh rest of thier lives.
It is understood the patient with CJD was operated on at the hospital two weeks before their diagnosis.
The HSE says Beaumont Hospital is now getting advice from the Irish Panel on CJD and from world experts in the UK - who have dealt with similar cases in the UK and worldwide.
In a statement Beaumont Hospital says while the number of patients potentially affected is low and confined to one area of surgery, the hospital will have a helpline open from 8.00am
The number is 1800 302 602
Head of Health Protection at the HSE Kevin Kelleher says they were informed of the diagnosis at the end of last week: