Hepatitis A is a liver disease caused by the hepatitis A virus (HAV). The incubation period of hepatitis A is usually 14–28 days. Symptoms of hepatitis A range from mild to severe, and can include fever, malaise, loss of appetite, diarrhea, nausea, abdominal discomfort, dark-colored urine, and jaundice (a yellowing of the skin and whites of the eyes). Infected children under 6 years of age do not usually experience noticeable symptoms, and only 10% develop jaundice. Among older children and adults, infection usually causes more severe symptoms, with jaundice occurring in more than 70% of cases. Because of the often asymptomatic or subclinical course of hepatitis A infection, estimated incidence rates are often underestimated. Review data from 1990 to 2005 suggest a global increase from 117 million HAV infections in 1990 to 121 million infections in 2005.