Age at acquisition of Helicobacter pylori infection: comparison of a high and a low prevalence country.

Helicobacter pylori (HP) is now generally accepted as the main aetiological agent in chronic active gastritis and peptic ulcer. Infection with HP is widespread, but the routes of transmission are still unclear. Several studies have shown increasing prevalence of antibodies against HP with age. In developing countries, age at peak incidence of seroconversion is probably considerably lower than in developed countries. We performed a cross-sectional study to determine the age at maximum incidence of seroconversion to HP in a high-prevalence country (Ethiopia) and in a low-prevalence country (Sweden). Sera from 242 Ethiopian children, aged 2-14 years and from 295 Swedish children aged 1-15 years were analysed using an enzyme linked immunosorbent assay (ELISA) for detecting immunoglobulin G (IgG) antibodies. In Ethiopia, a comparison was made of a local and a reference strain for preparation of the antigen, but there was little difference in outcome. A comparison between antigen prepared from the reference strain and the pooled antigen used in the Swedish study also showed little difference. The sharpest rise in seroprevalence was found in the age range 2-4 years. Among 4-year-olds, some 60% had already seroconverted, and among 12-year-olds almost 100% had done so. In Sweden, the sharpest rise appeared between the ages of 9 and 10 years. Above 10 years of age seroprevalence was around 20%. Infection with HP is acquired in early childhood in Ethiopia, but somewhat later, although still before the teens, in Sweden. To determine properly the risk factors for infection with HP, possible exposure must be assessed around the age of seroconversion, since seropositivity may remain for a long time but environmental factors may have changed since primary infection.