It is estimated that 257 million people worldwide, or approximately 5% of the global population, have chronic HBV infection. Areas of high endemicity for HBV infection, such as sub-Saharan Africa and Asia, are also most affected by the HIV pandemic.¹ HIV and HBV infections occur commonly together because of their shared routes of transmission. The prevalence of chronic HBV infection in people with HIV infection in Australia is approximately 5%.²

HBV is not directly cytopathic, and viral pathogenesis is largely immune mediated. Necroinflammatory changes in liver tissue that characterise chronic HBV infection are a result of cellular immune responses to viral antigens.³ Infection in endemic countries usually occurs very early in life, either through vertical or early horizontal transmission. The disease then passes through four different phases determined by the host immune response. These are the immune tolerant, immune clearance, immune control and immune escape phases and are characterised by varying levels of HBV viral load and necroinflammatory activity.¹ HIV infection significantly modifies this natural history as described below.