IBD prevalence in Lothian, Scotland, derived by capture-recapture methodology

Abstract

Objective: IBD prevalence is estimated to be rising, but no detailed, recent UK data are available. The last reported prevalence estimate in the UK was 0.40% in 2003. We aimed to establish the current, and project future, prevalence in Lothian, Scotland.

Design: We conducted an all-age multiparameter search strategy using inpatient IBD international classification of disease (ICD-10) coding (K50/51)(1997-2018), IBD pathology coding (1990-2018), primary and secondary care prescribing data (2009-2018) and a paediatric registry, (1997-2018) to identify 'possible' IBD cases up to 31/08/2018. Diagnoses were manually confirmed through electronic health record review as per Lennard-Jones/Porto criteria. Autoregressive integrated moving average (ARIMA) regression was applied to forecast prevalence to 01/08/2028.

Results: In total, 24 601 possible IBD cases were identified of which 10 499 were true positives. The point prevalence for IBD in Lothian on 31/08/2018 was 784/100 000 (UC 432/100 000, Crohn's disease 284/100 000 and IBD unclassified (IBDU) 68/100 000). Capture-recapture methods identified an additional 427 'missed' cases (95% CI 383 to 477) resulting in a 'true' prevalence of 832/100 000 (95% CI 827 to 837).Prevalence increased by 4.3% per year between 2008 and 2018 (95% CI +3.7 to +4.9%, p<0.0001). ARIMA modelling projected a point prevalence on 01/08/2028 of 1.02% (95% CI 0.97% to 1.07%) that will affect an estimated 1.53% (95% CI 1.37% to 1.69%) of those >80 years of age.

Conclusions: We report a rigorously validated IBD cohort with all-age point prevalence on 31/08/2018 of 1 in 125, one of the highest worldwide.

Keywords: Crohn’s disease; epidemiology; inflammatory bowel disease; ulcerative colitis.

Figure 1

Information sources used for IBD case identification. The number of unique cases of putative IBD identified from each information stream, and overall, during the described capture period. All gastroenterology secondary care outpatient appointments between 01/08/2017 and 01/08/2018 at the largest Lothian IBD centre (Western General Hospital) were screened in addition to estimate accuracy of our search strategy. All ‘possible’ cases were then submitted to manual review of the electronic medical record.

Figure 2

The point prevalence of IBD in Lothian on 31/08/2018. True and false positive cases were identified from ‘possible’ cases in figure 1 and used to define accuracy rates for each information stream (Table 3). True positives were screened for prevalent (Lothian postcode) and live (linkage to national datasets) cases to report point prevalence on 31/08/2018.

Figure 3

Age group prevalence breakdown by sex and IBD classification. Prevalent IBD cases were subdivided into age groups by IBD diagnosis into all IBD (red) and UC, CD or IBDU (blue). Percentage prevalence is reported for age-appropriate population data derived from National records for Scotland, 2016-based projections for 2018. CD, Crohn’s disease; IBDU, IBD unclassified.

Figure 4

Incidence, mortality and age at diagnosis by IBD subtype changes between 2008 and 2018. Incident cases were identified by using the date of diagnosis obtained during case verification. Mortality data were obtained from national registry linkage. Incidence and prevalent IBD cohort mortality (A), with IBD subtype incidence breakdown (B), age at diagnosis for prevalent cases on 31/08/2018 overall (C) and for IBD subtype (D). CD, Crohn’s disease; IBDU, IBD unclassified.

Figure 5

Projected IBD prevalent cases±95% CI from 2018 to 2028. Retrospective prevalence data were imputed monthly from 01/01/2008 to 31/08/2018 to model age-group projected future prevalence to 31/08/2028 (A), with absolute prevalent case number per age group for actual prevalence on 31/08/2018 and projected prevalence on 01/08/2028 (B). 2016-based population projections were obtained from 2018 to 2028 from National records for Scotland data.