[Barry Marshall] spent the next several years trying to convince experts that H. pylori might be the culprit behind ulcers. He met indifference and disbelief, but eventually study after study strengthened the link between this bacterium, ulcers and inflammation of the stomach.

The controversy lies in the fact that even though most people with ulcers have H. pylori in their stomach, most people with H. pylori never develop ulcers. However, H. pylori does seem to play a part not only in ulcers but also in chronic inflammation of the stomach, and even stomach cancer.

Other incriminating evidence against H. pylori is this: Although standard treatment of ulcers with acid-blocking drugs works, the ulcers recur in most people once they stop taking them. But not in most people treated for H. pylori.