Seasonal variations in onset of symptoms in Crohn's disease

BackgroundSeasonal variations in onset of symptoms have been reported in ulcerative colitis but not in Crohn's disease.Aim.To investigate whether our inflammatory bowel diseases patients presented seasonal variations in onset of symptoms.Patients and methodsPatients with a diagnosis of inflammatory bowel diseases established between 1995 and May 2004, and consecutively observed from June 2003 to May 2004, were included in the study. Onset of symptoms (year, season and month) was recorded. Expected onsets with a uniform distribution during the year were calculated and compared to observed onsets. Statistical analysis: chi-square test, odds ratio (95% confidence interval).ResultsOverall 425 inflammatory bowel diseases patients were enrolled. Onset of symptoms (year and season) was established in 353/425 patients (83%; 150 Crohn's disease; 203 ulcerative colitis). Onset of symptoms in inflammatory bowel diseases patients as a whole occurred more frequently in spring–summer compared to autumn–winter (odds ratio 1.39; 95% confidence interval 1.03–1.87; p < 0.03). This variation was observed in Crohn's disease (odds ratio 1.59; 95% confidence interval 1.00–2.51; p < 0.05) and a similar trend, although not significant, was observed in ulcerative colitis (odds ratio 1.27; 95% confidence interval 0.86–1.88; p = 0.27).ConclusionsThese data indicate that onset of Crohn's disease symptoms occurred more frequently during spring-summer. A similar trend was observed in ulcerative colitis. Environmental factors, such as associated infections, smoking, use of drugs and seasonal changes in immune function may be responsible for triggering the clinical onset of inflammatory bowel diseases.