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 by contaminated instruments that have not been subjected to special sterilisation techniques.
The condition is a degenerative neurological disorder which is incurable and invariably fatal.
The HSE said its now checking medical records to determine how many other patients were operated on using the same instruments.
It is understood the patient with CJD was operated on at the hospital two weeks before their diagnosis.
Kevin Kelleher, Head of Health Protection at the HSE, said way in which the contamination was discovered is unusual.
"There is no test that you can easily do when people are alive - it's normally diagnosed after death,"
"Here, there was some tissue available which they were testing routinely, and they were surprised to find it showed CJD."
He also said the risk of transmission is low, but those affected will need to be carefully monitored.
The HSE said 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 8am today.
Sinn Féin's Health Spokesperson Caoimhghín O Caoláin has called for an immediate review of hospital procedures.
Concerned patients may call the helpline on 1800 302 602.