Acute hepatitis B

**Definition:** Acute liver injury and inflammation caused by recent and short-term (less than 6 months) infection with hepatitis B virus (HBV). Transmission is by sexual, blood and body fluid contamination (parenteral spread), and from mother to baby at the time of birth (vertical transmission). Diagnosis is confirmed by presence of recent acquisition of HBsAg, ideally with IgM-anti-HBc in serum. Clinical features, if they occur, are characterised by anorexia, nausea and fever, with jaundice in severe cases.

**Long definition:** Acute hepatitis B is acute liver injury caused by infection with hepatitis B virus (HBV), which is a double-stranded and circular DNA hepadnavirus. The disease is transmitted parenterally (direct transfusion of blood and blood products, accidental or deliberated needle puncture including intravenous drug abuse, tattooing, acupuncture, and ear piercing) or by sexual contact. HBV surface antigen (HBsAg) is usually positive in the acute phase of the disease and acute HBV infection is diagnosed by the presence of high-titer serum IgM anti-HBc. Although acute hepatitis B is usuallyself-limiting, a fulminant course is more common than for hepatitis A. Further, chronic infection may occur in 2-5% of adults, but in most young children (under age of 3 years), and is also more common in renal failure and with HIV infection or other immunodeficient states. Acute liver failure is occurs in ~1% of cases. A varying proportion of cases (>90% of babies, <5% if adults, higher with immune deficiencies) develop chronic HBV infection, with or without liver disease.