H. pylori mixed infections have been found to involve more than one allele of either the s-region or m-region of vacA [22–24]. The rates of mixed infections may differ in cag-PAI of H. pylori isolated from the corpus and antrum  or there may be discrepancies in the antimicrobial susceptibility tests . The rates of mixed infections vary from 0% to 85% in different populations worldwide [14, 22, 26–28]. However, the prevalence of H. pylori mixed infections isolated from patients in Taiwan remains unknown. In this study, we characterized six isolates from each patient using genotyping analysis. The association between mixed infections in H. pylori clinical isolates from Taiwanese patients and disease severity was assessed.