Alpha diversity showed that the richness indices (Ace, Chao and Observed OUTs) of gastric microbiota were significantly higher in CAG patients than in nCAG patients (P < 0.05) in the patients with Hp-I infection; however, among the patients with Hp-II infection, no differences of the richness indices were observed between CAG patients and nCAG patients (P > 0.05). Here, HP is linked to infection.