HAV: general epidemiology, routes of transmission and groups at risk

Hepatitis A is an infectious disease caused by the hepatitis A virus (HAV). It is endemic throughout the world, though a few countries or regions report only sporadic infections. According to global estimates, 1.4 million people contract the disease each year. Hepatitis A normally occurs as an enteric infection acquired through contact with contaminated fecal matter. Iinfection is usually spread by the fecaloral route, i.e. by ingesting contaminated food or water or by direct person-to-person contact. Inadequate water treatment systems are a major source of transmission. In addition, mollusk-like oysters and clams that trap and concentrate HAV in sewage-contaminated water are another significant source of infection if they are eaten raw or cooked at temperatures below 185° F (85° C) for 1 minute. However, even adequately cooked food can be contaminated through inappropriate handling. Hepatitis A virus distribution is worldwide, but the different levels of risk for the disease are directly related to levels of sanitation and hygiene. The prevalence of hepatitis A virus has decreased substantially over the past few decades in many parts of the world. Improvements in socioeconomic status and sanitation (including household income, education, water quality and quantity, and hygiene) are largely behind the decreasing rate of anti-HAV seroprevalence in the population. With these improvements in sanitation, a shift in age of infection towards older age groups has been observed in many countries, with a resulting increase in symptomatic illness. As well, minor cyclical variations of incidence have appeared, with peaks occurring during the fall and winter that primarily involve people who travel to endemic countries during the summer holidays.