Hepatitis E is endemic to developing countries in tropical areas with poor sanitation. The main regions of endemism include central and southeast Asia, North and West Africa, and Mexico. In such areas, HEV may be responsible for more than half of acute, sporadic hepatitis cases. Large outbreaks are almost universally associated with fecally contaminated drinking water. It is unclear how the disease remains in the population between these outbreaks. Person to person transmission may maintain the infection, but such transmission is relatively rare (CDC "Hepatitis E Virus"). Primates, pigs, cows, sheep, goats, and rodents are also susceptible to the disease. In endemic areas 42-67% of goats, cows, and sheep are seropositive for HEV, but it is unclear whether any of these species act as a reservoir (WHO “Hepatitis E”).
The prevalence of HEV antibodies in humans is higher in non-endemic areas and lower in endemic areas than initially expected. In the U.S. about 2% of people possess anti-HEV immunoglobulins; the source of their infection is unknown. The majority of symptomatic hepatitis E cases occur in travelers returning from endemic areas, but the prevalence of antibodies indicates that exposure and subclinical infection may occur within the United States. In endemic regions, approximately 3-26% of people have anti-HEV antibodies. These antibodies are not found in infants and young children, while young adults have the highest prevalence (Knipe 3058). In general, infections occur most frequently in people between the ages of 15 and 40 (CDC Fact sheet:Viral Hepatitis E ).