H. pylori (previously known as Campylobacter pyloridis) is a type of bacterium that infects the stomach and is a common cause of peptic ulcers. H. pylori bacteria can be passed from person to person through direct contact with saliva, vomit, or fecal matter. It can also be spread through contaminated food or water. Infection is normally acquired during childhood and goes undiagnosed until symptoms of peptic ulcers appear. H. pylori infection is very common and is present in about half the people in the world.