Hepatitis B virus infection.

1. Brief description of the condition/disease Hepatitis B virus (HBV) is transmitted through percutaneous or permucosal exposure to blood or body fluids, producing an acute or chronic infection. Most acute infections are asymptomatic. Fewer than 10% of children and 33% of adults have acute hepatitis B, which often results in hospitalization and -- in approximately 0.1% of patients -- in acute hepatic failure and death. HBV regularly produces chronic infection in infants (90%) and young children (30-60%) and, less frequently (1-6%), in older children, adolescents, and adults. Among adults, chronic HBV infection can cause death from chronic liver disease (CLD, e.g. cirrhosis) or primary hepatocellular carcinoma (PHC). The risk for a liver-disease-associated death among persons with chronic HBV infection is 25% for those who acquired infection as an infant or young child, and 15% for those who acquired infection as an adolescent or adult. HBV infection also can produce extrahepatic manifestations, including polyarteritis nodosa and membrano-proliferative glomerulonephritis. The prevalence of chronic HBV infection varies worldwide; it is highly endemic ([is greater than] 8% prevalence) in Africa, the Pacific Islands, parts of South America, and most of Asia, as well as in ethnically defined populations in Australia, New Zealand, and the USA. The high prevalence of infection is sustained by transmission during the perinatal period and early childhood. In populations with intermediate endemicity (2-8% prevalence), perinatal and early childhood transmission accounts for most HBV infection. Endemicity is low ([is less than] 2% prevalence) in Australia, New Zealand, Western Europe, and the USA. Most acute infections occur among adolescents and adults, but perinatal and early childhood infections contribute substantially to the prevalence of chronic infection, and populations in which HBV infection is highly endemic may reside in these areas. 2. Current burden and rating within the overall burden of disease Estimates derived from regional data on prevalence of infection in the general population indicate that 360 million people worldwide have chronic HBV infection: 78% in Asia; 16% in Africa; 3% in South America; and 3% in Europe, North America and Oceania combined. Of these 360 million HBV-infected people, 55-92 million (15-25%) are expected to die at 45-55 years of age from HBV-related CLD. An estimated 1 million people die annually from HBV-related CLD or PHC. Although etiology-specific death rates for CLD are not available in most countries, CLD or PHC is among the live leading causes of death among adults in many developing countries. In countries in which HBV infection is highly endemic, most CLD is HBV-related; in countries in which endemicity is low, such as the USA, 10-15% of CLD is HBV-related. 3. Feasibility (biological) of elimination/eradication Immunization with plasma-derived or recombinant hepatitis B vaccine confers a high level of protection against acute and chronic infection. Pre-exposure vaccination prevents [is greater than] 95% of infections, and postexposure vaccination of infants at risk for perinatal infection prevents 90-95% of infections. The initial vaccination series confers protection against chronic infection for at least 15 years, and HBV transmission has been eliminated in populations 10 years after introduction of routine infant vaccination. Most chronically infected persons remain so over their lifetime, but their potential infectivity decreases because of the decline in HBV titre ([HB.sub.e]Ag-positivity). The combined effects of immunization and declining infectivity make elimination of HBV infection feasible. Eradication of HBV infection requires sustained elimination of transmission over the number of years needed for persons with chronic infection to be no longer in the population. The increased use of effective antiviral agents to treat chronic HBV infection could hasten its elimination. …