The Health, Labor and Welfare Ministry confirmed Tuesday that a patient contracted AIDS from a transfusion of HIV-tainted blood that had cleared the Japanese Red Cross Society's virus-detection test.
A public testing organization has found that the HIV gene sequences of the donated blood were identical to those in the blood of the patient who received the transfusion, ministry officials said.
It was Japan's first confirmed HIV infection from a transfusion of donated blood since the Red Cross introduced its current testing system in 1999, they said.
The tainted blood tested negative for HIV in May.
The donor tested HIV-positive when he attempted to give blood again in November, and a stored sample of the blood was found infected with the AIDS virus when retested with a more advanced method.