The incidents are not a serious threat, writes Dr Muiris Houston, Medical Correspondent.
The first documented human blood transfusion took place in France in 1667. Despite its success the practice was banned until the early 1800s, and the development of blood transfusion as a science did not occur until blood groups were discovered in 1901.
Since then the practice has become part of mainstream medicine. The risk of spreading viruses through blood transfusion was recognised after the discovery of HIV/AIDS. This led to renewed emphasis on the careful selection and testing of donors.
Although whole blood products are still transfused following major surgery and road traffic accidents, it is now possible to separately transfuse platelets, red cells and other individual components of blood, to suit a particular clinical need.
The process of irradiating blood is carried out to destroy cells called lymphocytes. As a key component of the immune system, lymphocytes in the transfused blood can attack the recipient's tissue when it "sees" a difference between it and the recipient's own blood. This reaction is called graft-versus-host disease and can happen when the person receiving a transfusion is immunocompromised. Although a very rare occurrence, graft-versus- host disease has a death rate of 80 per cent or greater.
Patients with cancer of the blood, such as lymphoma or leukaemia, often have severely impaired immune systems and must be given irradiated blood transfusions. The process is carried out at a blood centre using a specially designed irradiation unit.
A separate process, called leucocyte depletion, removes almost all white cells in a unit of blood. Introduced by the Irish Blood Transfusion Service (IBTS) in 1999, this process, although not as effective as irradiation, indirectly helps prevent the graft-versus-host reaction.
The over-irradiation of blood renders it useless as the cells are destroyed, so it does not represent a risk to patients, but merely a waste of blood product. However, under-irradiation may prevent eradication of the immune cells and allow graft-versus-host disease.
The failure of the Munster IBTS centre does not represent a serious threat to patients. The vast majority of cancer patients would not have been affected. Overall the incidents represent a minor rather than a major problem for the IBTS and the health service here.