A CAPTURE-RECAPTURE ESTIMATE OF INFLAMMATORY BOWEL-DISEASE PREVALENCE- THE FLORENCE POPULATION-BASED STUDY

Background. A recent population-based epidemiological study identified the patients with a diagnosis of ulcerative colitis or Crohn's diseas e resident in the metropolitan Florence area bz the period 1978-1992 a nd destined their vital status on 31 December; 1992. Aims. To estimate the completeness of Inflammatory Bowel Disease prevalent case ascerta inment in the study area. Subjects and methods. In a Registry, specifi cally developed during the study: 767 patients fulfilled the criteria for the definition of prevalent cases as of 31 December 1992, Ar the s ame time, we had access to an indepent source of potential patients: t he Regional Health Department kept a list of all Inflammatory Bowel Di sease patients allowed free access to specific health care provided on ly to selected diagnostic categories. We then compared the two differe nt sources and used a capture recapture analysis to estimate the numbe r of cases missed by both sources. Results. A total of 331 patients, w ere reported by both sources, 436 were found only in the Registry whil e a large group, of potential cases not present in our Registry was fo und out in the List. After careful confirmation of the diagnosis for e ach individual patient and contact with his/her physician, we identifi ed an additional 102 cases that were included in the final population series of 869 prevalent cases. This capture-recapture analysis led to a revised estimate of 1,003 prevalent cases, suggesting that 134 patie nts had been missed by both sources, resulting in an Inflammatory Bowe l Disease prevalence rare of 186 per 100,000. Conclusions. According t o this method our previous study underestimated the true prevalence of 13.4% (95% confidence interval: 9.8-16.6%). On account of some degree of negative dependence between the two sources the loss was probably in the lower range of this interval. Completeness of case ascertainmen t should be evaluated and discussed in all studies designed to provide population-based estimates for health care planning.