Helicobacter pylori is a gram-negative, microaerophilic bacterium that inhabits various areas of the stomach and duodenum. It causes a chronic low-level inflammation of the stomach lining and is strongly linked to the development of duodenal and gastric ulcers and stomach cancer. Over 80% of individuals infected with the bacterium are asymptomatic.

More than 50% of the world's population harbour H. pylori in their upper gastrointestinal tract. Infection is more prevalent in developing countries.