Both duodenal and gastric ulcer disease are closely associated with Helicobacter pylori infection. An infected individual has an estimated lifetime risk of 10-20% for the development of peptic ulcer disease, which is at least 3-4 fold higher than in non-infected subjects. H. pylori infection can be diagnosed in 90-100% of duodenal ulcer patients and in 60-100% of gastric ulcer patients. Subjects infected with a cytotoxin-producing bacterial strain, or a strain possessing cagA, are at a higher risk of duodenal ulcer. Other factors that may influence the peptic ulcer risk in infected subjects are the amount of gastric acid production (which is increased in duodenal ulcer disease and decreased in gastric ulcer disease), the presence of gastric metaplasia in the duodenal bulb, smoking, and genetic factors (e.g. blood group O and lack of the secretor gene). After eradication of the infection, the risk of recurrence of ulcer disease is reduced to below 10% for gastric ulcer disease and to approximately 0% for duodenal ulcer disease.