High incidence of Crohn's disease in Canterbury, New Zealand: Results of an epidemiologic study

Background: Inflammatory bowel disease (IBD) has increased exponentially in industrialized nations over the last 50 years. Previous New Zealand studies have shown that IBD is less common than in other countries; however, clinical observations suggested a high incidence and prevalence of IBD in Canterbury, particularly Crohn's disease (CD). Aim: This study aimed to determine the descriptive epidemiology of IBD in Canterbury. Methods: Canterbury IBD patients, recruited using multiple strategies, gave informed consent, permission for clinical record review, completed a questionnaire, and were bled for DNA extraction as part of the Canterbury IBD Project. Cases were confirmed using standard criteria, and completeness of recruitment was validated using capture-recapture methods. Demographic and phenotypic data were extracted from case notes. One thousand four hundred twenty patients (715 CD, 668 ulcerative colitis [UC]) were recruited (>91% of Canterbury IBD patients). Results: In 2004, age-standardized (World Health Organization World Standard Population) IBD, CD, and UC incidence rates were 25.2, 16.5, and 7.6/100,000/year, respectively. The IBD, CD, and UC point prevalences on 1 June, 2005 were 308.3, 155.2, and 145.0/ 100,000, respectively. CD patients were more likely than UC patients to be female (61.4% vs. 47.1%) and to be younger (median age, 39.9 years vs. 43.7 years). The percent of IBD patients who were white was 97.5%. Conclusion: IBD is at least as common in Canterbury as in other western regions. CD incidence and prevalence are amongst the highest ever reported and are higher than for UC. IBD population characteristics are otherwise similar to other countries. The Canterbury IBD Project will be a valuable tool for future population-based IBD epidemiology and genetics research.