Aim 2: Utilize gene-array technology for whole genome assessment of bacterial virulence genes and specific bacterial gene expression to allow characterization of virulence proteins associated with pediatric Hp infection. The Hp isolated from the prospectively enrolled infected children (cases) in Aim 1, Hp strains obtained in follow-up of the two established cohorts who remain infected, as well as a retrospective analysis of 125 banked pediatric isolates linked to clinical, demographic and epidemiological data will be characterized. Specific emphasis will be on the analysis of isolates found in the following three disease categories: ulcers, gastritis, atrophic gastritis.