<p>Helicobacter Pylori (H. pylori) is a bacterium that lives in the human stomach. Infection does not usually produce symptoms, and spreads through saliva and fecal material. Prevalence increases with age, but differs dramatically among populations. In the USA, prevalence is less than 20 per cent at 20 years old and about 50 per cent at 50 years, which may be typical of high-income countries, while in Korea, it is 50 per cent at 5 years and 90 per cent at 20 years, and in Japan it reaches 85 per cent by middle age.</p><p>H. pylori colonises the gastric mucosa and elicits both inflammatory and immune lifelong responses, including the release of various bacterial and host-dependent cytotoxic substances. H. pylori infection greatly reduces the bioavailability of vitamin C. this may play a role in the development of stomach cancer in the presence of dietary and other factors that are a cause of this cancer. In studies of precancerous lesions or gastric atrophy, eradication of H. pylori promoted regression of these cancer precursors.</p><p>Some people develop stomach cancer without apparent infection with H. pylori. Reported percentages of non-cardia cancers that test positive for H. pylori range from approximately 60 to 95 per cent, averaging around 86 per cent, but those with distal stomach cancer who test negative for H. pylori may have undergone a loss of infection associated with the atrophic gastritis, and consequently a decline in antibody titre. It can be regarded as a necessary cause for those stomach cancers arising in the distal region of the stomach.</p><p>The longer the time of infection, and the greater the impact on the gastric mucosa, the more likely it is that stomach cancer will develop and take a severe form. The exact site of the cancer is most likely to be where the mucosa is most affected. Those who develop extensive gastritis and gastric atrophy are at increased risk of developing cancer.</p><p>It was famously linked with stomach ulcers by two Australian researchers (Barry Marshall and J. Robin Warren)-one of whom deliberately infected himself to prove the theory- who were awarded the Nobel Prize for their discovery in 2005. The World Health Organization also classes the H. pylori as a leading cause of stomach cancer. Preventing stomach cancer by eradicating H. pylori in high-risk regions should be a priority.</p>
