Hepatitis B virus (HBV) infection remains a global major public health issue, although the vaccine and the continuous development of antiviral treatment are available [1]. It is estimated that approximately 240 million people worldwide are infected with HBV, which causes about 600,000 deaths each year [2]. It has been reported that China is a highly endemic country for HBV infection; approximately 100 million people who are HBV carriers and nearly 300,000 deaths due to HBV-related diseases each year [2]. With the introduction of highly sensitive hepatitis B antigen (HBsAg) assays, transfusion-associated HBV infection has been significantly reduced, it still exists the residual risk of transfusion-transmission of occult HBV infection (OBI).

OBI is defined as the presence of replication competent HBV DNA in the liver (i.e.episomal HBV covalently close circular DNA), and/or HBV DNA in the blood (usually at levels <200 IU/mL) of individuals with undetectable HBV surface antigen (HBsAg) by currently available assays, and with/without hepatitis B core antibodies (anti-HBc) and/or hepatitis B surface antibodies (anti-HBs), outside the pre-seroconversion window period (WP) [3].

The prevalence of OBI is variable worldwide, and even higher in areas where HBV is endemic 4. Studies estimated that the rate of HBV transmission from donors with OBI to recipients of blood components varies widely, from 2 to 48% [4], [5], [6], [7]. OBI donors indicate no evidence of liver damage, but OBI has been associated with higher risk of chronic infection progression and hepatocellular carcinoma (HCC) with the presence of other causes of liver damage, such as HIV or HCV co-infection [1,8].

Global implementation of nucleic acid testing (NAT) for HBV DNA has significantly eliminated the residual risk of HBV transfusion-transmission by reducing the diagnostic preseroconversion WP as well as detection for OBI infection. However, HBV transmission remains the most frequent transfusion-transmitted viral infection. To date, investigations of OBI features among blood donors from Northern China are still insufficient. This study investigated the prevalence of OBI in a blood donation center in beijing, and explored the genetic characteristics of OBI, all of which would provide useful clues for reducing the risk of transfusion-transmissible infectoins (TTIs) in the future.