Helicobacter pylori (H. pylori) infection is a bacterial infection that causes stomach inflammation (gastritis), peptic ulcer disease, and certain types of stomach cancer. Helicobacter pylori infection is the most common cause of gastritis and peptic ulcer disease worldwide. Infections are very common and increase with age. By age 60, about 50% of Americans will be infected. However, recent studies show that fewer young people are becoming infected with Helicobacter pylori. Infection is very common in whites, Hispanics, and Asians. Helicobacter pylori infects the lining of the stomach and can also be found in stool, saliva, and plaque on teeth. Helicobacter pylori can be spread from person to person, especially if an infected person does not wash their hands thoroughly after defecating. Because many people can spread germs through kissing or other close contact, infections tend to cluster among family members and people living in nursing homes and other supervised facilities.