BACKGROUND: Conflicting data have been reported about the seasonal variation of inflammatory bowel diseases (IBD). The purpose of the present analysis was to assess the occurrence of seasonal variations in the endoscopic diagnosis of Crohn's disease (CD) and ulcerative colitis (UC). METHODS: The Clinical Outcomes Research Initiative (CORI) uses a computerized endoscopic report generator to collect endoscopic data from 73 diverse practice sites throughout the United States. We utilized the CORI database to analyze the date-specific occurrence of colonoscopy, as well as the colonoscopic diagnoses of CD and UC. Time trends were analyzed by autocorrelation, linear, and nonlinear regression. RESULTS: Between January 2000 and December 2003, the number of colonoscopies increased 4.1-fold. The proportion of colonoscopies with a CD diagnosis fell by 28%, and the proportion of colonoscopies with a UC diagnosis fell by 50%. The occurrence of neither CD nor UC was shaped by any clear-cut seasonal periodicity. However, the trends of the two diseases revealed strikingly similar patterns with four resembling peaks superimposed on their monthly fluctuations. CONCLUSIONS: Endoscopic diagnosis of IBD is unaffected by any seasonal variation. The decline in the diagnostic rate of colonic IBD may reflect a relative increase in the utilization of colonoscopy for colon cancer screening. The similarity in the monthly fluctuations of both IBD suggests that their incidence or flare-ups may be influenced by identical exogenous risk factors.
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