Since its discovery around 30 years ago, Helicobacter pylori has been identified as one of the most common bacterial infections in the world. The bacteria colonise the mucus lining of the stomach, usually from early childhood and throughout life. In most cases, people infected with H. pylori remain unaware of it and have no symptoms. In some cases however, the infection leads to life-threatening disease. Between 10 and 15 per cent of those infected will suffer from ulcers in the stomach or duodenum, and in as many as two per cent of cases the result will be gastric cancer