The HSE is recalling hundreds of patients in the West and North West for Hepatitis C screening.
It follows confirmation that a staff member at three of the regions hospitals was infected with the disease.
The healthcare employee worked in Letterkenny General Hospital, University Hospital in Galway and Mayon General between 2004 and 2008.
The HSE says the person was involved in a number of surgical procedures during that four year period.
Now over 450 former patients are being called in for what health officials say is precautionary screening.
They will be notified by post on Monday.