Following the “Technical and Operational Guidelines and Procedures for Blood Centers” issued by the Chinese Ministry of Health on December 31, 2011 , all six blood centers had the same approach for blood donor screening, requiring all blood donors to pass a routine pre-donation screening process that consisted of a medical history questionnaire, a brief physical examination, and pre-donation rapid screening. The medical history questionnaire included questions about their histories of sexually transmitted diseases, hepatitis, illegal parenteral drug use, sex with multiple partners, and men who had sex with men (MSM). If any of the above items screened positive, the donors were permanently deferred. The physical examination included body temperature, body weight, and blood pressure. Before blood collection, all donors underwent rapid testing at the collection sites for the hepatitis B surface antigen (HBsAg, Rapid Test Kit, Aikang Bio-technology Co., Ltd., Hangzhou, China) as well as rapid testing for Alanine Aminotransferase (ALT) (ALT Rapid Test Kit, Rongsheng Biological Pharmaceutical Co., Ltd., Shanghai, China) and hemoglobin (Hb) (Hemoglobin Assay Kit, Amyjet Scientific Inc., Wuhan, China). The donors with increased ALT levels or a reactive HBsAg result would be temporarily deferred, the samples and information were saved if donors tested HBsAg positive on the rapid test.