Definition: Hepatitis B is a viral disease process caused by the hepatitis B virus (HBV). The virus is endemic throughout the world. It is shed in all body fluids by individuals with acute or chronic infection. When transmission occurs vertically (from mother to child) or horizontally between small children during play, the infection nearly always becomes chronic. By contrast, when transmission occurs in adolescents/adults-usually via sexual contact, contaminated needles ("sharps"), and less often from transfusion of blood products-the infection usually resolves unless the individual is immunocompromised (e.g., infected with human immunodeficiency virus). Providing education about how to avoid risky behavior can play an important role in prevention.