Estimating the prevalence of inflammatory bowel disease in Portugal using a pharmaco-epidemiological approach

To estimate inflammatory bowel disease (IBD) prevalence in Portugal from 2003 to 2007, and to obtain disease, sex and age specific estimates.

A pharmaco-epidemiological approach based on intestinal anti-inflammatory (IAI) drugs consumption was used. Proportion of patients taking IAI drugs and mean prescribed daily dose (PDD) were estimated from a sample of 513 IBD patients. Assumptions were made about unknown parameters and sensitivity analysis performed: drug compliance (80% in base case; range 70-85%) and proportion of sulphasalazine used in IBD (52%; range 40-80%). Sex and age specific estimates were based on a proposed methodological extension and results from a nationwide (n = 5893) cross-sectional study.

IBD prevalence increased from 86 patients per 100 000 in 2003 to 146 in 2007. Regions more affected were Lisboa and Porto (173 and 163 per 100 000 in 2007, respectively). Prevalence increased from 42 and 43 per 100 000 in 2003 to 71 and 73 in 2007, respectively for ulcerative colitis (UC) and Crohn's disease (CD). In 2007, prevalence was higher in the 40-64 age stratum for UC (99 per 100 000) and in the 17-39 stratum for CD (121). Prevalence was consistently higher in females.

Portugal is half way between countries with the highest and lowest IBD prevalence, but is steeply making the road to the highest-level group. Despite limitations of the proposed methods, assumptions were reasonable and estimates seem to be valid. Feasibility and comparability of this methodology makes it an interesting tool for future studies on IBD epidemiology.