OBJECTIVE: The main objective is to study whether the month of birth is associated with the development of Crohn's disease (CD) in the Israeli Jewish population. BACKGROUND: It was suggested that perinatal exposure to infectious agents may have a role in the pathogenesis of CD. Due to the seasonal nature of some infections, a linkage between birth dates and a risk to develop CD would support such a hypothesis. Previous studies that addressed this question were conducted in Europe and differed in their findings. METHODS: Birth dates of 844 Jewish ulcerative colitis (UC) and CD patients from three medical centers representing the north, central, and the south of Israel were compared with the monthly rates of birth during the same period of time. The standard incidence ratio was used to define the risk to develop either disease according to the month of birth. The Score method was used for the evaluation of seasonality trends. RESULTS: Birth during the winter period in Israel was associated with increased risk to develop CD, whereas birth during the spring was associated with a reduced risk. The Score method for seasonality showed a significant peak during winter time in these patients (z = 2.02, p = 0.021). No such seasonal variation was noted for UC patients. CONCLUSIONS: A seasonal pattern was observed in the risk to develop CD but not UC. The findings may support the involvement of environmental factors in the pathogenesis of CD.
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