title: The epidemiology of microscopic colitis: a population based study in Olmsted County, Minnesota.
abstract: 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.
  
  
  METHODS
  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).
  
  
  METHODS
  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<0.001). Rates increased with age (p<0.001). By subtype, the incidence was 3.1 per 100,000 for collagenous colitis and 5.5 per 100,000 for lymphocytic colitis. Collagenous colitis was associated with female sex (p<0.001) but lymphocytic colitis was not. Prevalence (per 100,000 persons) on 31 December 2001 was 103.0 (39.3 for collagenous colitis and 63.7 for lymphocytic colitis).
  
  
  CONCLUSIONS
  The incidence of microscopic colitis has increased significantly over time, and by the end of the study, the incidence and prevalence were significantly higher than reported previously. Microscopic colitis is associated with older age, and collagenous colitis is associated with female sex.
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Internal Medicine, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905, USA. pardi.darrell@mayo.edu
authors.forename: Darrell S
authors.initials: DS
authors.lastname: Pardi
authors.forename: Edward V
authors.initials: EV
authors.lastname: Loftus
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Smyrk
authors.forename: Patricia P
authors.initials: PP
authors.lastname: Kammer
authors.forename: William J
authors.initials: WJ
authors.lastname: Tremaine
authors.forename: Cathy D
authors.initials: CD
authors.lastname: Schleck
authors.forename: W Scott
authors.initials: WS
authors.lastname: Harmsen
authors.forename: Alan R
authors.initials: AR
authors.lastname: Zinsmeister
authors.forename: L Joseph
authors.initials: LJ
authors.lastname: Melton
authors.forename: William J
authors.initials: WJ
authors.lastname: Sandborn
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D046729:Colitis, Collagenous / Q000453:epidemiology; D046728:Colitis, Microscopic / Q000175:diagnosis / Q000453:epidemiology*; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008910:Minnesota / Q000453:epidemiology; D017678:Sex Distribution