In general, the following statements can be made to summarize prevalence of H. pylori in Western countries:
H. pylori affects about 20% of persons below the age of 40 years, and 50% of those above the age of 60 years.
H. pylori is uncommon in young children.
Low socio-economic status predicts H. pylori infection.
Immigration is responsible for isolated areas of high prevalence in some Western countries.
Studies of sera from epidemiologists and Californians show that a 50% decline in the prevalence of H. pylori has occurred in the United States since 1968.