Which of the following is incorrect about Helicobacter pylori

A、Helicobacter pylori infection is an infectious disease and contagious disease;
B、Helicobacter pylori eradication should be carried out in patients with H.pylori infection (whether adults or children);
C、Eradication of Helicobacter pylori can effectively prevent the occurrence of gastric cancer;
D、Helicobacter pylori is a gram-negative bacterium that infects more than half of the world's population