Hep Mec Cohort in Zambia

Inclusion Criteria: Must meet the inclusion criteria for one of 5 groups, as follows: * Group 1 (rx-naive chronic hbv mono): 18+ years old, HBsAg-positive, HIV-negative, eligible for tenofovir-based therapy, reports taking therapy no more than 7 days (could have previously taken if has stopped \>1 year ago). * Group 2 (acute hbv mono): 18+ years old, HBsAg-positive, HIV-negative, acute/subacute onset of hepatitis signs and symptoms and ALT \>10 times upper limit of normal * Group 3 (rx-naive hbv/hiv coinfection): 18+ years old, HBsAg-positive, HIV-negative, eligible for tenofovir-based therapy, reports taking therapy no more than 7 days (could have previously taken if has stopped \>1 year ago). * Group 4 (rx-experienced coinfection with hbv persistence): 18+ years old, history of chronic HBV infection based on two tests 6 months apart, HIV-positive, at least 4 years of tenofovir-based antiviral therapy, currently HBsAg-positive * Group 5 (hbsag loss): 18+ years old, HIV-positive or negative, history of chronic HBV infection based on two tests 6 months apart, Currently HBsAg-negative confirmed by sensitive assay Exclusion Criteria: * Hepatitis C coinfection (antibody-positive and RNA-positive), current or recent (past 6 weeks) pregnancy, decompensated cirrhosis on physical examination, unlikely to remain in Lusaka for study duration