The emphasis in red is mine, of course. This is from:Epidemiology of Microscopic Colitis Subtypes
Microscopic colitis (lymphocytic colitis or collagenous colitis) is a form of IBD that has not been studied epidemiologically in the United States until now. Using the Rochester Epidemiology Project in Minnesota (a medical records linkage system), 131 cases of microscopic colitis were identified over a 17-year period.[15] The mean age at diagnosis was 68 years, and 69% of subjects were women. Lymphocytic colitis, but not collagenous colitis, was found to be much more common among women (5.3:1). Age- and sex-adjusted incidence rates were about twice as high for lymphocytic colitis as for collagenous colitis. Additionally, incidence rates for microscopic colitis have been rising dramatically since 1985 (from 0.8/100,000 in 1985-1989, to 19.1/100,000 in 1998-2001). Such a rapid rise in incidence rates points toward an environmental (ie, infectious) etiology for this chronic disease.
http://www.medscape.com/viewarticle/480243
Of course, part of the rapid rise in incidence rates may be due to the fact that you can't find MC unless you look for it, and you can't find it unless you know how to find it.
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