Stomach cancer risk, which is linked to diet (World Cancer Research Fund/American Institute for Cancer Research, 2007), smoking (Secretan et al., 2009) and H pylori infection (International Agency for Research on Cancer, 1994) was strongly correlated with higher population density, higher levels of unemployment and lower levels of educational attainment, for both men and women. Crowded housing appears to be related to higher rates of H pylori infection (Brown, 2000), consistent with the observed association with population density. There was no significant difference in risk between NI and RoI. Overall geographical variation was marked, and similar for men and women. For women a band of higher risk was seen from north Dublin, through Louth, Cavan, Monaghan and west Fermanagh to Donegal. This increased risk was almost entirely on the RoI side of the border. For men, there was no area of increased risk in Fermanagh, and the high relative risk was almost entirely confined to RoI. For both men and women there was an area of higher risk in Belfast city (which presumably explains the similar risk in RoI and NI despite the pattern described above) and for women a few isolated areas of higher risk in west Kerry, west Galway and Wicklow.
As H pylori is easily diagnosed and treated, the relationship between H pylori prevalence rates and geographical variation in stomach cancer should be investigated at a community level.
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