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Abstract
Although the incidence and prevalence of ulcerative colitis and Crohn's disease are
beginning to stabilize in high-incidence areas such as northern Europe and North America,
they continue to rise in low-incidence areas such as southern Europe, Asia, and much
of the developing world. As many as 1.4 million persons in the United States and 2.2
million persons in Europe suffer from these diseases. Previously noted racial and
ethnic differences seem to be narrowing. Differences in incidence across age, time,
and geographic region suggest that environmental factors significantly modify the
expression of Crohn's disease and ulcerative colitis. The strongest environmental
factors identified are cigarette smoking and appendectomy. Whether other factors such
as diet, oral contraceptives, perinatal/childhood infections, or atypical mycobacterial
infections play a role in expression of inflammatory bowel disease remains unclear.
Additional epidemiologic studies to define better the burden of illness, explore the
mechanism of association with environmental factors, and identify new risk factors
are needed.