Background and methods: To investigate the acquisition rate of Helicobacter pylori infection among Finnish adults, we obtained, in 1991, serum samples from 181 subjects who were shown to have histologically normal, noninfected gastric mucosa in 1974-76.
Results: During the 15-year follow-up period 12 (6.6%) of the 181 subjects developed H. pylori antibodies (IgG), the overall annual acquisition rate being 0.44%. The acquisition rate correlated somewhat with age. Antibodies developed in 1(4.5%) of the 22 subjects less than 40 years old (in 1991) and in 4 (31%) of 13 subjects who were 70 years old or older. If it is assumed that H. pylori acquisition is a continuous and stable event through the whole life span, and the rate is similar in all birth cohorts, the observed annual acquisition rate of 0.44% or an increase of this rate with age does not explain the current prevalence of chronic gastritis in Finland. Extrapolations of the known and estimated prevalence rates of chronic gastritis in 1974/76 and 1991 indicated rather that the H. pylori acquisition is a birth-cohort-dependent phenomenon and that most of the acquisitions occurred in childhood in every cohort (generation). After being high in childhood (less than 20 years old), the acquisition rate exponentially slowed down with age in all cohorts.
Conclusions: Among adults the acquisition rate of H. pylori infection is low, and the main period of acquisition is childhood. The relationship between the acquisition rate and age is inverse and exponential.