The epidemiology of microscopic colitis: a population based study in Olmsted County, Minnesota

Objective: Although the epidemiology of microscopic colitis has been described in Europe, no such data exist from North America. We studied the incidence, prevalence and temporal trends of microscopic colitis in a geographically defined US population. Design and setting: In this population based cohort study, residents of Olmsted County, Minnesota, with a new diagnosis of microscopic colitis, and all who had colon biopsies for evaluation of diarrhoea, between 1 January 1985 and 31 December 2001 were identified. Biopsies were reviewed for confirmation (cases) and to identify missed cases (diarrhoea biopsies). Main outcome measures: Incidence rates, age and sex adjusted to the 2000 US white population. Poisson regression assessed the association of calendar period, age and sex with incidence. Results: We identified 130 incident cases for an overall rate of 8.6 cases per 100 000 person-years. There was a significant secular trend, with incidence increasing from 1.1 per 100 000 early in the study to 19.6 per 100 000 by the end (p