GSTM1 and hepatitis B virus infection: Occult hepatitis B infection (OBI) refers to a condition where replication-competent hepatitis B virus (HBV)-DNA is present in the liver, with or without HBV-DNA in the blood [<200 international units (IU)/ml or absent] in HB surface antigen-negative/HB core antibody-positive (HBsAg−/HBcAb+) individuals (1).