Did the inheritance of a pathogenicity island modify the virulence of Helicobacter pylori?

Strains of Helicobacter pylori from patients with peptic ulcer disease and gastric cancer contain a 40-kb fragment of DNA that is not present in isolates from carriers with asymptomatic infections. The discovery of the cag pathogenicity island suggests that virulence has evolved by quantum leaps through the inheritance of one or more DNA insertions.