Demography and presentation of chronic hepatitis B virus infection.

Currently, >350 million people worldwide are affected by chronic infection with the hepatitis B virus (HBV). Chronic infection may cause cirrhosis and hepatocellular carcinoma; HBV infection is responsible for 328,000 cancer deaths per year. In areas of high HBV endemicity, most infections occur early in life; infected children do not mount an effective immune response and exhibit immune tolerance, so that the risk of chronic infection is high. In areas of low endemicity, infections tend to be in adults within defined risk groups, and the risk of chronicity is much lower. Population migration from areas of high endemicity to areas of low endemicity is creating pockets of HBV infection in areas of low general prevalence, necessitating improved efforts to screen, vaccinate, and treat. Chronic HBV infection is a complicated, nonlinear disease with a variable course of progression; predictors of progression include the duration of time in the immunoactive phase of disease that follows the immune tolerant phase when hepatocytes are attacked. Additionally, the duration of a high viremic state, with ongoing clinical hepatitis and possibly concurrent infections (e.g., hepatitis C, human immunodeficiency virus), influence outcome. Targeted vaccination of high-risk groups has many limitations. Universal childhood vaccination to prevent chronic infection and its sequelae is the only approach that will lead to the global elimination of chronic HBV infection.