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Between 1993 and 2003, blood from the patient was used both for transfusions and to make medicines, which were given to thousands of patients, health officials said. All were at least potentially exposing them to mad cow disease, whose route of transmission is still poorly understood, scientists say. .
Ten patients are known to have received direct blood transfusions, which pose the highest risk. Far more received medicines like gamma globulin and clotting factors, which are made from blood, and whose level of risk is unknown. .