Poster Session II - A272 EVOLUTION OF UC:CD INCIDENCE RATIOS ACROSS EPIDMIOLOGIC STAGES

TL;DR

The study shows that the ratio of ulcerative colitis to Crohn's disease incidence decreases over time as inflammatory bowel disease progresses through different epidemiologic stages.

Contribution

The novel contribution is the analysis of UC:CD incidence ratios across epidemiologic stages using global data and statistical modeling.

Findings

The UC:CD incidence ratio decreases significantly during stages 1 and 2 before stabilizing in stage 3.

Meta-analyses confirmed a progressive shift toward a 1:1 UC:CD ratio across stages.

Outliers were observed in Asia and northern latitudes, suggesting regional variations in IBD epidemiology.

Abstract

Inflammatory bowel disease (IBD) progresses through distinct epidemiologic stages: Stage 1 (Emergence), low incidence/prevalence; stage 2 (Acceleration in Incidence), rapid increasing incidence; stage 3 (Compounding Prevalence), stabilizing incidence and increasing prevalence. As IBD emerges in a population, ulcerative colitis (UC) incidence typically exceeds Crohn’s disease (CD) incidence, but over time the UC:CD incidence ratio approximates 1.

To examine changes in UC:CD incidence ratios across epidemiologic stages.

Stage classifications were previously determined by machine-learning classifier applied to data from 522 population-based studies of 82 countries (1920–2024). Population-weighted mean incidence (excluding zeros) was used to calculate annual, country-specific UC:CD ratios. Ratios were analyzed using a generalized additive model for location, scale, and shape (GAMLSS), accounting for overdispersion and skewness, with pairwise Wilcoxon rank sum tests and Bonferroni correction for between-stage comparisons. Average annual percent changes (AAPC) with 95% confidence intervals (CI) were calculated for each country within each stage. AAPCs were pooled by meta-analysis within stages. Outliers were defined using the Tukey method and are presented separately.

The GAMLSS model, adjusted for country, showed significant effects of epidemiologic stage on UC:CD incidence ratios (p<0.001), highlighting a progressive shift toward a 1:1 ratio (Figure 1). Significant differences were found between stages: Stage 1: Median: 3.62 (IQR: 3.9 [1.66–5.56]); Stage 2: Median: 1.8 (IQR: 2 [1.12–3.12]); Stage 3: Median: 1.56 (IQR: 1 [1.08–2.08]); all comparisons: p<0.001. Meta-analyses supported these results, decreasing in stages 1 and 2 before stabilizing in stage 3: Stage 1 (13 countries, 1954–2022) AAPC: −4.77 (95%CI: −8.59, −0.95); stage 2 (42 countries, 1952–2022) AAPC: −2.55 (95%CI: −4.04, −1.06); stage 3 (24 countries, 1970–2023) AAPC: −0.12 (95%CI: −0.66, 0.42). Outliers (n=81; 7.8%) were primarily observed in Asia and northern latitudes (Table 1) (eg, China, Faroe Islands).

The UC:CD incidence ratio significantly decreases during stage 1 and 2, then stabilizes in stage 3. Recognising stage-specific changes in the UC and CD incidence may clarify the epidemiologic evolution of IBD and guide research into environmental and diagnostic determinants.

A272 Table 1: UC:CD Incidence Ratio Outliers

CIHRThe Leona M. and Harry B. Helmsley Charitable Trust; International Organization for the study Inflammatory Bowel Disease (IOIBD)

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