Increasing Contribution of Adolescent Type 1 Diabetes Drives Incidence Rates in Poland - a 40-year-long Observational Study

Aims/hypothesis: 40-year-long longitudinal observation of long-term trends of type 1 diabetes incidence and prevalence in children in Central Poland  

Methods: This was a prospective observational study performed by a reference regional center for pediatric diabetes care for Lodz Province (currently 2·4M inhabitants, 360K children). We registered each case of new-onset type 1 diabetes admitted to regional pediatric diabetes centers between the years 1983 and 2022 in children between 0 and 14 y.o. The diagnosis was based on currently available guidelines. Cases of other types of diabetes (e.g., monogenic) were excluded upon identification from incidence and prevalence rates. Yearly data on the at-risk population were acquired from Poland`s General Statistical Office. Sex-specific data on population structure were available from 1989 onwards.  

Results: In the analyzed period, the incidence rate of type 1 diabetes increased tenfold from 3·29/100,000 (95%CI: 1·85-4·73) in 1983 to 32.43 (26·42-38·44) in 2022, with an average annual percentage change of 5·73% (95%CI: 4·99%-6·44%). Joinpoint analysis detected two distinct periods of increase: rapid in 1983-2005 (annual percentage increase of 7·38%, 95%CI: 6·30-10·52%) and a slower one in 2005-2022 (3·65%, 95%CI: -0·86-5·13%). Incidence rates among the youngest children (0-4 y.o.) were significantly lower than in 5-9 y.o. (β±SE: -0·567±0·059, p<0·0001) and 10-14 y.o. (β±SE: -0·520±0·060, p<0·0001). The incidence growth dynamic for the two older groups showed a consistent increase, whereas the incidence in 0-4 year-olds plateaued after 2007. Incidence rates varied seasonally, with the most cases diagnosed during the winter months (December, January, and February; mean difference from remaining seasons of 29±11·6 percentage points, p<0·0001). Corresponding with increasing incidence rate, estimated prevalence of type 1 diabetes increased over the years and reached 177·21/100,000 (95%CI: 163·18-191·24) for children 0-14 y.o., and  17·11 (95%CI: 9·2-25·02), 190·54 (95%CI: 165·03-215·75), 238·73 (95%CI: 211·7-265·76) for 0-4, 5-9, and 10-14 y.o., respectively. 

Conclusion/interpretation: Over the past 40 years, the incidence of type 1 diabetes in children in Central Poland has increased significantly, but the rate of increase appears to be slowing. As majority of patients with type 1 diabetes are 10 years old or older, with the most new cases occurring in that age group the healthcare systems should prepare for care of young adults who are extensive users of new diabetes technologies.