- Chronic hepatitis B virus (HBV) infection, defined as a positive test for hepatitis B surface antigen (HBsAg), unless the patient has been treated with a nucleos(t)ide analog (eg, tenofovir or entecavir) for at least 6 months and the HBV DNA by polymerase chain reaction (PCR) assay has been persistently undetectable for at least 6 months.