What is the causal relationship of H. pylori to upper gastrointestinal disease?  

A strong association between H. pylori and upper gastrointestinal disease has been reported. The causal relationship between H. pylori and chronic superficial gastritis is well established. 

The evidence for this statement is as follows:

Virtually all H. pylori-positive patients demonstrate antral gastritis.

Eradication of H. pylori infection results in resolution of gastritis.

The lesion of chronic superficial gastritis has been reproduced following intragastric administration of the isolated organism in some animal models and oral administration in two humans.  

The strongest evidence for the pathogenic role of H. pylori in peptic ulcer disease is the marked decrease in the recurrence rate of ulcers following the eradication of infection. The prevention of recurrence following H. pylori eradication is less well documented for gastric ulcer than for duodenal ulcer, but the available data suggest similar efficacy. 

In the case of duodenal ulcer, it is curious that in some studies the organism is more often present in the antrum than in the duodenum, where the ulcer is found. Suggested mechanisms by which an antral organism causes a duodenal lesion include bacterial colonization of gastric metaplasia in the duodenum, secondary changes in gastric acid or duodenal bicarbonate secretion, or changes caused by products of the infecting organism and/or the inflammatory response of the host. Further studies are needed to clarify the mechanisms of bacterial pathogenesis and host responses leading to duodenal ulceration.

To date, there is no convincing evidence for an association of H. pylori infection with nonulcer dyspepsia. The prevalence of H. pylori infection is no higher in patients with nonulcer dyspepsia than in the general population. Although some patients with nonulcer dyspepsia may have symptoms related to the presence of H. pylori, there are no data to demonstrate how to identify such a subset. Studies are needed to determine whether H. pylori-infected patients with nonulcer dyspepsia would benefit from treatment of the infection.