Aid in the diagnosis of H. pylori infection; determine the cause of chronic type B gastritis or ulcers of the stomach or duodenum. What is Helicobacter Pylori? Helicobacter pylori (H. pylori) is a bacterium that causes chronic inflammation of the inner lining of the stomach (gastritis) in humans. This bacterium also is the most common cause of ulcers worldwide. H. pylori infection is most likely acquired by ingesting contaminated food and water and through person to person contact. In the United States, 30% of the adult population is infected. (50% of infected persons are infected by the age of 60.)One out of every six patients with H. pylori infection will develop ulcers of the duodenum or stomach. H. pylori also is associated with stomach cancer and a rare type of lymphocytic tumor of the stomach called MALT lymphoma.