of more than half of the world's population. While the bacteria are present in over half of the world's population, infection does not necessarily cause symptoms, and thus most cases are asymptomatic. It has been suggested that H. pylori plays an important role in the natural stomach ecology.

While H. pylori is the most common infectious cause of gastritis, there are other pathogens that can cause the disease. Uncommon causes include those of the genera Cytomegalovirus and ''Candida''.