Increasing Incidence and Prevalence of the Inflammatory Bowel Diseases With Time, Based on Systematic Review

Natalie A. Molodecky; Ing Shian Soon; Doreen M. Rabi; William A. Ghali; Mollie Ferris; Greg Chernoff; Eric I. Benchimol; Remo Panaccione; Subrata Ghosh; Herman W. Barkema; Gilaad G. Kaplan

Disclosures

Gastroenterology. 2012;142(1):46-54. 

In This Article

Materials and Methods

Search Strategy

We conducted a systematic literature search using a predetermined protocol and in accordance with the quality of reporting meta-analyses of observational studies (MOOSE).[10] We searched 2 computer-stored databases, MEDLINE (1950 to December 2010) and EMBASE (Excerpta Medica Database; 1980 to December 2010) for studies investigating the epidemiology of IBD. The detailed search strategy was developed in consultation with a research librarian and is outlined in Appendix 1 . The search was not limited by language or human subjects to ensure capture of all appropriate papers. The reference lists of relevant articles were also reviewed.

Selection Criteria

Two reviewers (N.A.M. and I.S.S.) independently conducted an initial screen of identified abstracts and titles. Abstracts were eliminated in this initial screen if they were not observational and did not investigate the epidemiology of IBD. Studies that did not report original data (eg, review articles) were also excluded. Abstracts meeting these criteria were eligible for full-text review, and articles were independently considered for inclusion in the review if they reported an incidence rate and/or prevalence of UC and/or CD or adequate information to calculate incidence rates or the prevalence. UC and CD were required to be reported separately for inclusion in the systematic review. Reports describing the incidence or prevalence of only pediatric-onset IBD (ie, age of diagnosis younger than 16 years) were excluded because a systematic review on the incidence of pediatric-onset IBD has been published.[11] Disagreement between reviewers was resolved by consensus with third party experts (D.M.R. and G.G.K.).

Data Extraction

Prevalence studies were identified to highlight the burden of IBD globally, whereas studies reporting incidence assessed the temporal evolution of disease diagnosis as well as patient characteristics at diagnosis, including age and sex. Two reviewers independently completed data extraction forms for each study. Data on prevalence per 100,000 population with 95% confidence intervals for the overall study period were collected. The incidence rates per 100,000 person-years with 95% confidence intervals for the overall study time period as well as incidence rates for the following were documented: (1) time trends, (2) age groups, and (3) sex ratios.

Summarization of Data

The incidence of IBD was summarized using incidence rates, defined as the number of cases in a population over the person-years at risk in the population. When incidence rates were adjusted for confounding factors, these estimates were reported. An average incidence rate was calculated when incidence rates were reported separately for male and female subjects, for race/ethnicity, or over multiple years. Prevalence of IBD was defined as the number of prevalent cases in a defined region per 100,000 population. All studies were organized by geographic region. Geographic maps were created using ArcMap version 9.3 (Geosoft Inc, Toronto, Canada) to evaluate worldwide differences in incidence and prevalence of IBD. Choropleth maps displaying differences in incidence rates and prevalence with changes in color intensity were used. Division of color shades was determined using quintiles of incidence and/or prevalence in a single map. Additionally, maps specific for incidence and prevalence were created separately. Incidence rates or prevalence values for local jurisdictions in Canada, the United States, the United Kingdom, and Spain were extrapolated to the entire province/state. For other countries where incidence rates or prevalence values were provided for local jurisdictions, the estimates were averaged and assigned to the entire country's jurisdictions. When incidence or prevalence for a region was reported in multiple studies, an average was calculated. Maps were divided into 3 periods: (1) before 1960, (2) 1960 to 1979, and (3) 1980 to 2006. Meta-analyses were not performed due to variability in study design of included studies.

We conducted time-trend analyses for studies that reported incidence rates for periods spanning at least a 10-year period with at least 3 time points. When the incidence rate was reported for a multi-year period, the midpoint of the time interval was selected. Temporal trends were calculated with joinpoint regression analysis whereby a series of permutations were used to assess whether the addition of joinpoints resulted in statistically significant linear changes in the direction or magnitude of the rates in comparison with a linear line.[12] Two joinpoints at most were considered. The parameter estimate used to summarize the trend over the fixed interval was the average annual percentage change according to a generalized log-linear model that assumed a Poisson distribution.

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