An innocent baby & an unfortunate doctor

Two weeks back, there was a report in the newspaper about a little baby who was transfused with HIV positive blood, and is now showing symptoms of full blown AIDS.
Now this is the story, The baby was brought into the emergency clinic with need for an urgent blood transfusion, the father eventually offered to donate blood which as it the practice is not necessarily used to transfuse the baby but replaced in the blood bank. Another bag was taken out of the bag, and transfused to the baby, there were no improvements, and the baby started wasting. Diverse tests were carried out to ascetain what could be the problem. When the XYZ text (HIV) was carried out, the baby tested positive. How come? The father's blood and mother's blood samples were tested, and were found to be negative. When the donor from which the blood that was transfused to the baby was tested, he tested positive. Investigations commenced, and it was discovered that the donor tested negative at the time of donation. The donor was probably just seroconverting when his blood was taken, and the viral load was not high enough to be detected. The baby who had no preformed immunity against the Human Immunodeficiency virus now has symptoms of AIDS. Accusing fingers have been pointed at the doctor, some have said it was his fault, some have said it was machine error, some have blamed the hospital for not having up to date equipment to detect the least viral load.
The big question is Who is at fault?