Update 5pm: Blood donors and those who rely on transfusions are being reassured after a patient contracted Hepatitis B from a transfusion.
The Irish Blood Transfusion Service says the blood the person received had been tested, but the infection was not detectable at the early stage of infection.
The patient has made a full recovery and is now clear of Hepatitis B.
Earlier: A patient has been infected with Hepatitis B from a contaminated blood transfusion, health chiefs have revealed.
The Irish Blood Transfusion Service (IBTS) described it as a one-in-two million incident and said it has no implications for future transfusions.
Hepatitis B or HBV is a common infection of the liver, affecting millions of people around the world every year.
Most adults with normal immune systems will clear the infection although the young, old or sick can suffer chronic symptoms.
The IBTS said the infection is not a "test failure".
It said an investigation by Grifols/Hologic, the manufacturer of the assay used to test for the virus, confirmed it performed to the expected standard of sensitivity.
Dr Stephen Field, IBTS medical and scientific director, said: "The IBTS wishes to stress that this is a rare one in two million event - and does not have any implications for blood that will be transfused to patients in the future.
"The IBTS has tested 1.2m donations to date and there has been no other confirmed transfusion transmitted infection of Hepatitis B."
The IBTS said an archived sample of the blood donation tested negative using one of the most sensitive molecular screening assays available but a subsequent discriminatory test for HBV virus DNA was positive.
The patient is being managed appropriately by a medical team, the IBTS said.