History and epidemiology of hepatitis A virus.

Hepatitis A was clearly recognized as an entity separate from other types of hepatitis during World War II, but only later did studies provide convincing evidence of the prevalence and transmission of hepatitis A virus (HAV). Disease incidence varies over time and geography, with wide differences from country to country and even within cities. Noted recently is a shift in prevalence in cases from childhood to adulthood. Incidence figures are unreliable. Epidemiology of the disease is best defined by measurement of anti-HAV antibodies. HAV is a very stable virus, frequently found in urban sewage. Infections occur early in life when sanitation is poor and living conditions crowded, but improvements in sanitation and hygiene have delayed infection, resulting in increasing numbers of adults susceptible to HAV. Transmission of HAV by blood is rare. High-risk persons include injection drug users, institutionalized persons and their caretakers, and those who travel from low-prevalence to high-prevalence countries.