High incidence of inflammatory bowel disease in Australia: a prospective population-based Australian incidence study.

Background: To date, there have been no population-based epidemiological studies published from Australia concerning the incidence of inflammatory bowel disease (IBD). Our hypothesis was that the incidence of IBD in Australia is at least as high as other industrialized countries, given similar genetic and environmental risk factors.

Methods: A prospective, population-based IBD incidence study was conducted between April 2007 and March 2008 in Greater Geelong, Victoria, Australia. According to 2006 Australian Census data, this comprises an at-risk population of 259,015. Cases were ascertained from multiple overlapping sources. All local general practitioners, gastroenterologists, surgeons, and pediatricians were contacted every 2 months to identify new IBD cases. The Royal Children's Hospital in Melbourne, local endoscopy and pathology centers were also searched to ensure completeness of case capture. Standard IBD case definitions were used with clinical, endoscopic, and histological criteria.

Results: In all, 76 new cases of IBD were identified during the 1-year period. There were 45 cases of Crohn's disease, 29 of ulcerative colitis, and 2 of indeterminate colitis. The crude annual incidence rates for IBD overall, Crohn's disease, ulcerative colitis, and indeterminate colitis were 29.3 per 100,000 (95% confidence interval [CI] 23.5-36.7 per 100,000), 17.4 per 100,000, 11.2 per 100,000, and 0.8 per 100,000, respectively. When directly age-standardized to the World Health Organization standard population the overall IBD incidence rate was 29.6 per 100,000.

Conclusions: This is the first prospective, Australian population-based IBD incidence study. The incidence rates are among the highest reported in the literature of IBD.