Helicobacter pylori infection is thought to be the most common bacterial infection worldwide. Whilst the prevalence of H. pylori is decreasing rapidly in Europe, Australia and the USA, where on average 10-15% of the adult population are infected, it remains a significant problem in China, where serological studies in adults still show seroprevalence rates above 70%. Recent data from Auckland, New Zealand (2012), indicated high prevalence of infection in Maori (35%), Pacific peoples (31%) versus Europeans (8%).

H. pylori colonisation is associated with active gastritis but the vast majority (70%) of patients remain asymptomatic. H. pylori  remains on the surface and does not invade the epithelium of the gastric mucosa.  The bacteria are associated with peptic ulcers, gastric cancer and lymphoma. For an excellent review of upper GIT microbiota including Helicobacter and its associations with disease and health, see  Walker and Talley 2014.