Epidemiology

According to a Swedish study, the prevalence of microscopic colitis among patients undergoing colonoscopy for evaluation of chronic watery diarrhea is between 10% and 20%.[10][11]​ Microscopic colitis accounts for almost 20% of cases of chronic diarrhea in patients >70 years.[11][12]​ The estimated incidence rate of microscopic colitis worldwide is 11.4 cases per 100,000 person‐years.[6] In the UK, the incidence is estimated to be around 18 cases per 100,000 population per year.[13] Studies from North America and Europe suggest a rising incidence in the late 20th century.[14] However, data from the early 2010s suggest that incidence rates have stabilized.[10][15]​ In North America and Europe, the incidence of the collagenous colitis subtype ranges from 0.6 to 16.4 cases per 100,000 person-years, while the incidence of the lymphocytic colitis subtype ranges from 0.6 to 16 cases per 100,000 person-years.[6] Geographic variations in the incidence of microscopic colitis have been reported, although conclusions cannot be made due to the limited number of studies and the lack of direct comparative studies from different countries for the same time period.[6]

More than 75% of patients diagnosed with microscopic colitis are over 45 years of age.[16] The median age at diagnosis for collagenous colitis is 64.9 years, similar to lymphocytic colitis (median 62.2 years); a raised incidence of microscopic colitis is observed with increased age.[10] Microscopic colitis can also affect children, particularly those with autoimmune diseases and those frequently taking medications associated with microscopic colitis, such as nonsteroidal anti-inflammatory drugs.[16] However, it is very rare in pediatric populations.[4]

The risk of developing microscopic colitis is higher in women than men.[10] In three large studies, the average proportion of females with microscopic colitis was 72%.[17][18][19] In case series, a female to male incidence ratio of 2.8 to 4.1 was reported for collagenous colitis and 1.7 to 2.6 for lymphocytic colitis.[17][19][20]

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