Introduction to epidemiology and risk of hepatitis B

The most important modes of transmission of hepatitis B virus (HBV) are sexual, needle stick (both accidental or through intravenous drug use), blood transfusion or from mothers to newborns. The outcome of HBV infection mainly depends on the immune response of the host but is also influenced by the capability of the virus to escape defence mechanisms by integration into the genome of the host's hepatocytes. These factors affect whether HBV infection leads to acute hepatitis or remains asymptomatic, whether the infection resolves to immunity or becomes chronic and whether chronic clinical sequellae such as chronic hepatitis, liver cirrhosis or hepatocellular carcinoma develop. The epidemiological status of a given country with regard to HBV depends on socioeconomic factors, the proportion of individuals with risky life styles, the pre-existing prevalence of HBV, the vaccine programme available and compliance to hygienic measures.