Seasonal variations in the clinical of presentation of Crohn's disease and ulcerative colitis.

Epidemiological evidence that Crohn's disease could be a transmissible condition is limited. The case histories of 211 patients with Crohn's disease and 201 patients with ulcerative colitis have been scrutinized to ascertain whether there is a seasonal variation in the onset of symptomatic disease. Crohn's disease has a peak onset in January and July whereas ulcerative colitis has a possible peak of onset in December. A hypothesis is proposed that these findings provide epidemiological evidence, suggesting that Crohn's disease could be a transmissible condition, and that Crohn's disease and ulcerative colitis may not be aetiologically related.