The incidence of type 1 diabetes in children under 15 years of age is rising again-a nationwide study.

International incidence rates (IRs) and trends of childhood type 1 diabetes (T1D) vary. Recent data from Ireland and other high incidence countries suggested a stabilisation in IRs of T1D in children aged under 15 years. Our primary objective was to report the IR of T1D in children in Ireland from 2019 to 2021 and evaluate if age, sex and season of diagnosis had changed. Incident cases of T1D in those aged under 15 years were identified prospectively by clinicians nationally and reported to the Irish Childhood Diabetes National Register (ICDNR). Following case verification, capture-recapture methodology was applied, and IRs calculated. Numbers of children including age, sex and season of diagnosis per year were evaluated. There were 1027 cases, 542 males (53%). The direct standardised incidence rates (SIRs) increased by 21% overall and were 31.1, 32.2 and 37.6/100,000/year, respectively, with no significant sex difference. The highest IRs were in the 10-14-year category until 2021, then changed to the 5-9-year category (40% of cases). Whilst autumn and winter remain dominant diagnostic seasons, seasonality differed in 2021 with a greater number presenting in spring. CONCLUSION: The incidence of childhood T1D in Ireland is increasing, observed prior to the COVID-19 pandemic, and shifting to an earlier age at diagnosis for the first time. The pattern of seasonality also appears to have changed. This may reflect an increased severity of diabetes with important implications for healthcare providers. WHAT IS KNOWN: • Ireland has a very high incidence of T1D in childhood, which had stabilised following a rapid rise, similar to other high incidence countries. • The incidence rate is consistently highest in older children (10-14 years). WHAT IS NEW: • Irish IR is no longer stable and has increased again, with the highest incidence occurring in the younger 5-9 age category for the first time. • The seasonality of diagnosis has changed during the COVID-19 pandemic years of 2020-2021.

Is the incidence of type 1 diabetes in children and adolescents stabilising? The first 6 years of a National Register.

The Irish Childhood Diabetes National Register (ICDNR) was established in 2008 to define accurately the incidence and monitor the epidemiology of type 1 diabetes (T1D) in the Irish population. Here, we report data from the first 6 years of the National Register and compare with previous national data. Prospective national incident data regarding T1D in those under 15 years resident in Ireland were collected from 2008 to 2013 and national incidence rates (IRs) calculated. Ascertainment completeness was assessed using capture-recapture methodology. The period identified 1566 new cases of T1D, ascertainment reached 96.8 % in 2013. The standardised incidence rate was 27.5 in 2008 stabilising at 28.7 and 28.8 cases /100,000/year in 2012 and 2013. There was no evidence that the incidence changed significantly in the 6-year period either overall or for each age group and gender. There was evidence of a difference in the incidence of T1D across the age groups with the overall incidence highest in the 10-14 year age category. A strong seasonal association was demonstrated. CONCLUSIONS: This study confirms Ireland as a high-incidence country for type 1 diabetes whilst demonstrating that the previous marked increase in IR from 16.3 cases/100,000/year in 1997 has not continued. Ongoing monitoring through the robust mechanism of the ICDNR is required to clarify whether this is a fluctuation or if the incidence of T1D diabetes has stopped rising in our population. Alternatively, this apparent stabilisation may reflect a shift to a later age at diagnosis. "What is known :" • The incidence of Type 1 diabetes (T1D) is increasing in most populations worldwide although in certain high-incidence populations, it may be stabilising • There was a marked increase in T1D in Ireland between 1997 and 2008 • T1D incidence increases with affluence "What is New:" • The high incidence of T1D in Ireland has been confirmed at 28.8 cases/100,000/year in 2013 and has been effectively stable in the period 2008-2013 • Incidence is highest in Irish 10-14 year olds • Changes in incidence possibly reflecting life style and economic climate • Marked seasonality of diagnosis confirmed.