The Japanese Red Cross Society has confirmed the first case in which donated blood containing the hepatitis C virus passed its screening tests and was used in a blood transfusion, according to officials of the organization.
The contaminated blood was donated in western Japan in November 2000 and the Red Cross detected hepatitis C genes in a followup test on the individual blood samples it kept.
In June the society began to recheck samples of donated blood at the instruction of the Health, Labor and Welfare Ministry.
It believes the screening system, which tested blood from 50 donors together at the time of donation, failed to detect the virus because the amount of the virus was small.
The contaminated blood was used in a transfusion to a patient with stomach cancer in December 2000. The patient, who died of the cancer eight months later, was not tested for the virus.
The latest finding means the highly sensitive screening test, introduced in 1999, has failed to detect all three viruses for which it was designed -- hepatitis B and C and the AIDS-causing HIV.
The Red Cross said earlier that more than 6,400 units of blood for use in transfusions shipped since June 2002 may be contaminated with hepatitis or other viruses.