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Table 148-1

Epidemiology of IBD

Ulcerative ColitisCrohn's Disease
Incidence (North America) per person-years0-19.2 per 100,0000-20.2 per100,000
Age of onset15-30 and 60-8015-30 and 60-80
EthnicityJewish > non-Jewish white > African American > Hispanic > Asian
Male/female ratio0.51-1.580.34-1.65
SmokingMay prevent disease (OR 0.58)May cause disease (OR 1.76)
Oral contraceptivesNo increased riskOR 1.4
AppendectomyProtective (risk 13-26% lower)Not protective
Monozygotic twins6-18% concordance38-58% concordance
Dizygotic twins0-2% concordance4% concordance

Abbreviation: IBD, inflammatory bowel disease; OR, odds ratio.