Viral deletions among healthy young Chinese adults with occult hepatitis B virus infection.

To investigate the mechanism and prognosis of occult hepatitis B virus (HBV) infection (OBI) at a molecular level among healthy young adults, the presence of HBV DNA in 1176 sera samples collected from healthy young people after neonatal vaccination was assessed by nested polymerase chain reaction (PCR) using specific primers designed for the X and S regions of the HBV genome. Full-length HBV DNA from 9 patients with OBI (OB1-OB9) was cloned and sequenced. Deletions in the pre-S, basal core promoter (BCP), core (C) and polymerase (P) regions were observed. The data indicate that there is still a substantial risk of OBI in China despite neonatal vaccination. All deletions that were observed in the pre-S, BCP, C and P regions play a direct or indirect role in OBI. The presence of a deletion mutation in the pre-S1 region was considered to play a pivotal role in hepatocarcinogenesis and was found to increase the risk of hepatocellular carcinoma in the cohorts studied.