Is Helicobacter pylori good or bad?

Helicobacter pylori remains a controversial organism with regards to humans, with its epidemiology still being unclear nearly two decades after its discovery. The association between H. pylori infection and subsequent development of chronic active gastritis, peptic ulcer disease, gastric cell carcinoma, and B cell mucosa-associated lymphoid tissue (MALT) lymphoma has been well established. Current studies, however, suggest that fewer than 20 % of all infected patients will develop any consequences from their infection. Hence, should the infection be considered a disease not at all or, on the contrary, is the microorganism harmful in only some circumstances? This article attempts to weigh the currently available evidence supporting that H. pylori may be good and not always bad.