Baseline sera from 74 volunteers without a history of typhoid fever who were immunized orally with CVD 908-htrA were tested by enzyme-linked immunosorbent assay for immunoglobin G ( IgG ) antibodies to H. pylori , hepatitis A antibodies ( a marker of low socioeconomic status and exposure to enteric infections ) , and pepsinogen ( PG ) I and II levels ( measures of gastric inflammation ) .