“…A specific group of patients who are seronegative on HBsAg but seropositive on HBV DNA has been identified, and their infection defined as occult hepatitis B (Hu, 2002;Torbenson & Thomas, 2002;Chen, 2005). Although occult hepatitis B has long been documented (Hoofnagle et al, 1978), it was difficult to investigate it before the availability of HBV polymerase chain reaction (PCR). The molecular and immunological mechanisms underlying occult hepatitis B still remain incompletely elucidated.…”