Patients who were treated with the drug, which was produced by Guangdong Bioyee Pharmaceutical Co. Ltd, have been tested and none have so far contracted hepatitis C, said Zhang Jixiang, SFDA spokesman.

    The patient tests were conducted by the National Institute for the Control of Pharmaceutical and Biological Products and the clinical testing center of the health ministry.

    Some patients have tested positive for hepatitis C antibodies which Zhang says is a result of having taken the blood-based drug which was designed to boost a patient's immune system.

    "We can conclude that the hepatitis C antibodies in the drug were caused by contaminated blood plasma which the company bought illegally," said Zhang.

    According to medical expert Jia Jidong, the patients are unlikely to contract hepatitis C if the blood product contained only antibodies but no virus.

    "The antibodies will disappear in several months," said Jia, of the Chinese Medical Association.

    Hepatitis C is a liver disease and although symptoms are relatively mild compared with other types of hepatitis, it can become chronic and lead to liver cancer.

    On Jan. 16, the Health Ministry announced it was revoking the manufacturing certificates of the Bioyee and Haikou Kangliyuan Group. Both were found to be violating production standards following an investigation last December.

    The company's blood-based drug was sold in 12 regions including Beijing, Shanghai, Fujian and Shandong. At least 90,000 doses of the drug have been recalled, according to SFDA.

    SFDA and the health ministry said further investigation and risk assessment are continuing and more information will be released as soon as possible.