Dublin's Crumlin hospital has confirmed it has made contact with the parents of 15 out of 18 of the children involved in a contamination scare at Our Lady's Hospital.
The problem came to light after a crack was found in a colonoscope that was used during procedures on children between the May 17 and July 5.
Tests on the equipment found the presence of a bug in a crack in the damaged scope.
The hospital says an information pack and a sample kit to test for the bug is being sent to each of the affected families.
It says results will be returned immediately and full support given to any family whose child tests positive.
The hospital has apologised for the incident and is emphasising that there is no immediate impact on children's health.
Clinical director Colm Costigan said the bug is not an infection - but it may "colonise" if the children test positive.
He said there is no immediate risk to those involved.