Incidence of a clinical diagnosis of the irritable bowel syndrome in a United States population

Background: The incidence of irritable bowel syndrome is uncertain. We aimed to determine the incidence of clinically diagnosed irritable bowel syndrome in the community. Methods: Using the Rochester Epidemiology Project, all diagnoses of irritable bowel syndrome made among adult residents of Olmsted County, Minnesota, over a 3-year period were identified. The complete medical records of a random sample of the potential subjects were reviewed for the 10 years prior to the irritable bowel syndrome diagnosis and any patient who had received a previous diagnosis of irritable bowel syndrome was excluded (prevalent cases). Results: The diagnostic index listed 1245 possible irritable bowel syndrome patients; 416 patient charts were reviewed and, of these, 149 were physician diagnosed incident cases of irritable bowel syndrome. The age- and sex-adjusted incidence rate was 196 per 100 000 person-years and increased with age (P = 0.006). The age-adjusted annual incidence per 100 000 in women was higher than in men: 238 vs. 141 (ratio 3:2; P = 0.005). The overall symptom frequency at the time of diagnosis was abdominal pain (73%), diarrhoea (41%) and constipation (16%). Conclusions: The incidence of a clinical diagnosis of irritable bowel syndrome in adults was estimated to be two per 1000 per year, increased with age and was higher in women than men. As many people with irritable bowel syndrome do not seek care, the true incidence of irritable bowel syndrome is likely to be higher.