[Epidemiology of Helicobacter pylori infection in Japan]

The prevalence of H. pylori infection in Japan is extremely low at an early age, as in other developed countries, and subsequently shows a rapid increase until it reaches a plateau of about 70% at 50 years of age. This phenomenon is thought to occur because people about 50 years old were born soon after World War II and spent their childhood in conditions of poor hygiene. It is suggested that H. pylori infection leads to histological chronic gastritis regardless of the strain of this organism, and after that the course of the disease does depend on the environmental factors such as diet, duration of or age at H. pylori infection, the virulence of H. pylori strains, and host factors including genetic make-up in Japan.