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Abstract

We thank Forss et al for their letter in response to our analysis on temporal trends in inflammatory bowel disease (IBD) and for raising important considerations in leveraging administrative data for epidemiologic research.1Agrawal M. et al.Gastroenterology. 2022; 163: 1547-1554Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar,2Forss A. et al.Gastroenterology. 2022; Google Scholar We recognize the variability and overall downward trend in the incidence of ulcerative colitis (UC) after an initial rise in a subgroup of patients aged ≥ 65 years. A potential explanation could be that in 2012, the International Classification of Disease, Tenth Revision code K52.3 for IBD unspecified/indeterminate colitis was introduced in Denmark. The code for IBD unspecified, as the name suggests, is applied in cases when the diagnosis may be ambiguous and can include non-IBD colitis, which notably is more common in the elderly. Inclusion of this code in the definition of UC is likely to contribute to false positives and artificially influence temporal changes considering that this code was introduced in 2012, which is within our study period of 1995–2016. For these reasons we did not include this code in our definition of UC. On the other hand, exclusion of this code from our definition of UC could potentially have led to the underestimation of UC incidence in the subgroup of patients aged ≥ 65 years. However, we found that during the study period, 2875 individuals had at least 1 registration with International Classification of Disease, Tenth Revision code K52.3. Of these, 978 individuals had a second Crohn’s disease or UC diagnosis code during follow-up, implying that a relatively small number of patients were diagnosed with K52.3 only (n = 1897). Therefore, the impact of misclassification, if any, is likely to be small. Other points support our inference. First, this code was introduced in 2012, and the downward trend in UC incidence in the elderly started a few years before that. Second, we conducted additional analyses to understand how incidence curves change on including the aforementioned code in the UC definition. We noted that the variability and downward trends persist. Last, on conducting sensitivity analyses with the application of different definitions of UC, we observed similar changes in UC incidence over time, corroborating a true change in incidence patterns. We take this opportunity to highlight the importance of a thoughtful and meticulous consideration of administrative codes to define outcome or exposure in epidemiologic research. Use of rigorous and consistent methodology, while also bearing in mind associated limitations, are key in leveraging administrative data for epidemiologic research and toward meaningful conclusions. We caution against haste in analysis or interpretation. Overall, our study reports on the rising IBD incidence across all age groups, alongside rising prevalence and aging of the IBD population over the last 2 decades. These findings are important because they pave the way toward understanding persistent risk factors for IBD and preparing healthcare systems for rising IBD burden and aging patients. Certainly, elderly-onset IBD is likely to represent a distinct subgroup with associated unique challenges and warrants inquiry in subsequent studies.3Jeuring S.F. et al.Inflamm Bowel Dis. 2016; 22: 1425-1434Crossref PubMed Scopus (105) Google Scholar The Burden of IBD: Comparing Denmark and SwedenGastroenterologyPreviewWe commend Agrawal et al1 for a well-conducted study on the incidence and prevalence of inflammatory bowel disease (IBD) in Denmark from 1995 to 2016. They found increasing prevalence and an age distribution shifting toward the elderly, consistent with previous findings from both Sweden and other countries.2,3 More surprising was the still increasing incidence of IBD and that the incidence of elderly-onset ulcerative colitis (UC) fluctuated in an extreme and implausible fashion during the study period. Full-Text PDF