Helicobacter pylori (H. pylori) is a spiral-shaped bacterium that is found in the gastric mucous layer or adherent to the epithelial lining of the stomach. H. pylori causes more than 90% of duodenal ulcers and up to 80% of gastric ulcers.nfection with H. pylori also causes duodenal and gastric ulcers. Infected persons have a 2- to 6-fold increased risk of developing gastric cancer and mucosal-associated-lymphoid-type (MALT) lymphoma compared with their uninfected counterparts. The role of H. pylori in non-ulcer dyspepsia remains unclear.