Still, other physicians point out that esophageal cancer is rare, whereas stomach cancer is the 14th-leading cause of cancer death worldwide. Beyond the effects of physicians treating H. pylori with antibiotics, the microbe is losing ground as community water supplies become cleaner and as overall hygiene improves. H. pylori infection is less common among the well-off than the poor, and less common in small families than large ones. These factors in part explain why it's less prevalent in developed countries than in developing countries. Since 1968, the number of people in the United States infected with H. pylori has dropped by 50 percent.
Similar trends are apparent in other developed countries.
A few studies have begun to differentiate the effects of H. pylori on different segments of the gastrointestinal tract. The work focuses on a virulent strain of H. pylori carrying a gene called cagA . This strain is more likely than others to cause ulcers and stomach cancer and also to prevent diseases of the upper stomach and esophagus, Blaser contends. Last year, a group of researchers working with Blaser showed that people with reflux disease, Barrett's esophagus, and esophageal cancer were less likely to be infected with cagA strains than people without these diseases were. The distribution of other strains isn't known.