Seasonal variations in the onset of ulcerative colitis in Japan

Figure 1 A flow chart of Japanese ulcerative colitis patients. Among 265 Japanese patients with ulcerative colitis observed for more than 12 mo between 1994 and 2006, a total of 198 patients were enrolled in the onset evaluation. Of these, 165 patients relapsed (239 times), and their symptom scores were recorded each month for at least one year in the relapse evaluation.

Figure 2 Monthly variations in the onset of ulcerative colitis. The highest onset rate was observed in October (24/198, 12.1%), followed by March (23/198, 11.6%). The lowest onset rate was observed in July and August (10/198, 5.1%). The timing of ulcerative colitis (UC) onset was characterized by a monthly variation (χ²_{(2 df)} = 8.43, P = 0.015), with a peak during October and March and a trough during June and September.

Figure 3 Seasonal variations in the onset of ulcerative colitis. The highest seasonal onset rate was observed in the winter (57/198, 28.8%), followed by the spring (55/198, 27.8%), autumn (53/198, 26.8%), and summer (33/198, 16.7%). A seasonal pattern was also observed (χ²_{(3 df)} = 7.88, P = 0.048), as the onset rate was highest during autumn to spring (observed/expected: 53/49.36, 57/48.82, 55/49.91, respectively).

Figure 4 Monthly variations in the relapse of ulcerative colitis. The highest monthly relapse rate was observed in October (27/239, 11.3%), followed by May (23/239, 9.6%). The lowest relapse rate was observed in January (11/239, 4.6%). Variations in relapse were not found on a monthly basis (χ²_{(2 df)} = 1.31, P = 0.52).

Figure 5 Seasonal variations in the relapse of ulcerative colitis. The highest seasonal relapse rate was observed in the autumn (70/239, 29.3%), followed by the spring (66/239, 27.6%), summer (58/239, 24.3%), and winter (45/239, 18.8%). There was no variation in relapse on a seasonal basis (χ²_{(3 df)} = 5.75, P = 0.12).

Figure 6 Causes of ulcerative colitis relapse. In most cases (85.3%), the causes of ulcerative colitis (UC) relapse were not identified (none). However, in cases with an apparent cause, upper respiratory inflammation was the main factor responsible for UC relapse in our Japanese sample.