How Common it is
An estimated 80,000 new cases a year; 1.25 million chronic carriers; death from chronic liver disease occurs in 15-25% of chronically infected persons.

How you catch it
Highly contagious. It's 100 times more infectious than HIV, the virus that causes AIDS. Highest rate of disease occurs in 20-49 year olds. Virus spreads through blood or body fluids (including during sex), through IV drug use, at a job involving exposure to human blood or body fluids. A fetus can get it from an infected mother. Theoretical risks: tattooing and manicures, although this seems to be very rare in this country.

How to prevent it
Vaccine (three doses, safe for pregnant women) now recommended for all babies, adolescents not already vaccinated, and adults at high risk. Immunoglobulin should be given to unvaccinated people within two weeks after exposure to infected blood or body fluids, and to newborns of infected mothers in addition to the vaccine.

How it affects you
In most adults the infection clears up completely. However, about 5 to 10% of infected adults (and 30 to 90% of children under age 5) develop a chronic form of the disease. Chronic infection increases risk of liver cancer and cirrhosis, and increases a pregnant woman's risk of miscarriage and premature labor. Interferon approved to treat chronic infections.