Background on HIV and HBV

Human immunodeficiency virus (HIV) infection andhepatitis B virus (HBV) infection, which overlap sincethey are transmitted by similar routes, including sex and injection drug use, have caused large global epidemics. HIV, a retrovirus with an RNA genome that has 2 variants (HIV-1 is most common in the United States), targets CD4 cells and damages the host immune system. HBV, a hepadnavirus with a DNA genome that has 8 genotypes, targets liver cells (hepatocytes), and also damages the host immune system. HBV is 50 to 100 times more infectious than HIV.1,2 While the tests (HIV-1 RNA viral load and CD4 cell counts) and clinical course for HIV infection are somewhat straightforward, the tests and clinical course for HBV are more complex. Chronic HBV infection is characterized by changes in HBV viral load (usually represented by viral counts in log units). Several tests measure HBV viral load and activity. The following are typical tests used to measure HBV viral load: