Hepatitis A is an extremely contagious infection of the liver. It is caused by the hepatitis A virus and causes inflammation of the liver which affects the liver’s ability to function. It is one of three of the most common types of hepatitis viruses: hepatitis A, hepatitis B, and hepatitis C. Hepatitis A is the mildest form of hepatitis. There are about 20,000 people in the United States who get hepatitis A every year.