Abstract Chris Amaechi

Helicobacter Pylori and stomach cancer mortality in England & Wales; the cohort effect.
¹C. Amaechi, ²M. Law
¹VU Medical Center Amsterdam, The Netherlands, ²Wolfson Institute of Preventive Medicine, St Bartholomew’s and the Royal London Hospital School of Medicine and Dentistry

Introduction
Stomach cancer remains one of the most common forms of cancer for men and women. Determinants of risk for stomach cancer are smoking and diet. Another major determinant of risk is Helicobacter pylori infection. Long-term infection of the stomach with this bacterium may lead to chronic atrophic gastritis, a possible pre-cancerous change of the lining of the stomach. H pylori is usually acquired in the first few years of life and stays in its host for life. The most important risk factors for infection are overcrowding and poor hygiene in the childhood home. As living conditions improved over the last century, H pylori prevalence has likely dropped. During the same period, stomach cancer mortality has also decreased. This paper, therefore, aims to explore the extent to which the decrease in stomach cancer mortality can be explained by the fall in prevalence of H pylori infection.

Material and Methods
A retrospective cohort study was carried out by analyzing data on mortality in England and Wales from 1940 to 2000. Trends in stomach cancer mortality for ten birth cohorts were observed and the risk of death from stomach cancer for each cohort calculated. This was then compared with an estimate of H pylori prevalence for each cohort to determine if there was any observable association.

Results
Each cohort at each age group showed a lower mortality than the cohort preceding it. For men, the cumulative risk of death from stomach cancer dropped from just above 7.1% in the earliest cohorts to 0.3% in the 1960 cohort. The female cohorts showed a drop from 5.1% to 0.2%. Combined, the risk of death dropped from 6.1% to 0.23%. A gradual but steady reduction in H pylori prevalence was observed from 1910 to 1960. The prevalence in 1910 was 78% compared to prevalence in 1960 of 23%.

Conclusion
Based on our findings, the fall in H pylori prevalence at best accounts for about a third of the decline in risk of death from stomach cancer. Other factors like smoking and diet have contributed to the decline in stomach cancer mortality. The extent of their contribution remains largely unknown. Future work should attempt to shed more light on these issues.

Keyword(s): Helicobacter Pylori, Cohort effect