A bacterium, first identified in 1982, which colonises the stomach of more than half the world's population. It usually causes no problem but has a tendency to produce inflammation – gastritis, which may progress in some people to peptic ulceration (see PEPTIC ULCER), and even to gastric cancer. The bacterium can be identified by detecting ANTIGEN in faeces, ANTIBODIES in saliva or blood or by a radioisotope breath test. Definitive diagnosis is by obtaining a biopsy of the stomach wall by ENDOSCOPY. It can be eradicated by treatment with PROTON-PUMP INHIBITORS and appropriate antibiotics. Because of increasing rates of bacterial resistance to the commonly used antibiotics, it is likely that immunisation against the organism will become standard in the distant future.