Hepatitis B virus infection has a worldwide distribution. It is estimated that, currently, more than 2 billion of the global population have been infected. Of these, approximately 360 million are chronically infected and at risk of serious illness and death from liver cirrhosis and liver cancer, diseases that are estimated to cause 500 000–700 000 deaths each year worldwide. Humans are the only reservoir of HBV.
The virus is highly contagious and is transmitted by percutaneous and permucosal exposure to infected blood and other body fluids (i.e. semen and vaginal fluid). Common modes of transmission include mother-to-infant, child-to-child, unsafe injection practices, blood transfusions and sexual contact. The incubation period is 75 days on average, but may vary from about 30 to 180 days. HBV may be detected in serum 30–60 days following infection and persist for widely variable periods of time.