THE COHORT EFFECT AND HELICOBACTER-PYLORI

A total of 631 serum samples collected in 1969, 1979, and 1989 from ad ults and children were screened for Helicobacter pylori by Western blo t analysis. Results showed that H. pylori seroprevalence has become le ss frequent over the 20-year period. By studying seropositivity by yea r of birth, the magnitude of a cohort effect of H. pylori seropositivi ty was estimated. The odds of being seropositive decreased by 26% per decade, P = .008 (95% confidence interval, 8%-41%). Estimates of serop revalence adjusted for both age-specific variation and the cohort effe ct suggest that most seropositivity in adults occurs by the age of 15 years. The implication of these findings is that H. pylori infection i s becoming less frequent and is predominantly acquired in childhood.