Biphasic annual periodicity in relapses of inflammatory bowel diseases. Gruppo di Studio per le Malattie Infiammatorie Intestinale.

We evaluate the periodicity in relapses of ulcerative colitis and Crohn's disease in this multicenter prospective study. In 275 relapses among 184 patients with inflammatory bowel disease, a statistically significant biphasic annual periodicity, with peaks in the spring and autumn, was documented only for ulcerative colitis relapses (p = 0.006). This finding may be important in understanding relapse risk factors and in terms of prevention.