About 2,200 people who tested positive for hepatitis and other contagious diseases while donating blood in fiscal 2002 had previous blood donation records, according to the Japanese Red Cross Society.
The Red Cross Society said that current blood-screening technology cannot detect certain viruses at the initial stage of infection and some of the infected donors may have slipped through the screening process and given tainted blood.
The study, conducted over a one-week period in early June, found blood donation records from 1,700 people who had been infected with hepatitis-B, 350 people infected with hepatitis-C, 70 people with HIV, the virus that leads to AIDS, and 70 people with syphilis.
The Red Cross Society said the blood given by these donors has been discarded but the blood that had been donated before they tested positive was turned into blood products, and some of these products have been given to patients.
The society said it has started recalling all possibly tainted blood products that remain in stock.
The Health, Labor and Welfare Ministry has found that the Red Cross Society failed to carry out followup studies to check whether blood donors who tested positive for contagious diseases had previously donated blood.
The ministry ordered the Red Cross Society on June 16 to retrieve all products that were produced from the possibly tainted blood.