Background: Since humans have been infected with Helicobacter pylori for millennia, it has remained an enigma why the occurrence of gastric and duodenal ulcer rose suddenly during 19th century. The study aim is to present a mathematical model of H. pylori epidemiology that explains the peculiar long-term trends of ulcer disease.
Methods: Gastric and duodenal ulcer mortality data from England and Wales between 1911 and 2000 were used to validate a model based on two simple and straightforward assumptions about H. pylori infection. First, the infection rate fell in the general population between 1,800 and 2,000. Second, gastric ulcer was caused by H. pylori infection contracted between the ages 5 and 15 and duodenal ulcer was caused by H. pylori infection contracted after the age of 15. As the infection receded in the general population, the two fractions of subjects who became infected between the ages 5 and 15 or after the age of 15 increased among consecutive birth cohorts.
Results: The analysis of the actual long-term mortality from gastric and duodenal ulcer indicates an underlying birth-cohort pattern. These birth-cohort patterns of gastric and duodenal ulcer could be simulated by the interaction of two opposing time trends, namely a declining infection rate and a rising fraction of individuals acquiring their infection at increasingly older ages. The superimposition of a declining and a rising trend resulted in a bell-shaped curve of ulcer occurrence affecting consecutive birth-cohorts born between 1830 and 1970. Similar to the real data, the modelled cohort pattern of gastric ulcer preceded that of duodenal ulcer by 20 years.
Conclusion: The birth-cohort phenomenon of ulcer disease can be explained by a receding H. pylori infection accompanied by a simultaneous shift in its age of acquisition.