Incidence of type 1 diabetes in Norway among children aged 0–14 years between 1989 and 2012: has the incidence stopped rising? Results from the Norwegian Childhood Diabetes Registry

Aims/hypothesis Our study aimed to describe the incidence of type 1 diabetes in children below 15 years of age in Norway during the period 1989–2012 and to assess the regional variation during 2004–2012. We further set out to estimate the completeness of ascertainment in the Norwegian Childhood Diabetes Registry (NCDR). Methods Incident cases of type 1 diabetes were registered in the NCDR and incidence rates were modelled using Poisson regression. Ascertainment for 2005–2008 was estimated using capture–recapture methodology by using data from the Norwegian Prescription Database (NorPD), a nationwide register established in 2004, which included insulin prescribed and dispensed at pharmacies to individual patients. Population data were obtained from Statistics Norway. Results Observed incidence rates for 1989–2012 suggested three distinct time segments: in 1989–1996, the average incidence rate was 22.6 per 100,000 person-years (95% CI 21.4, 23.7); in 1996–2004, the average incidence rate was 28.4 per 100,000 person-years (95% CI 27.3, 29.6); and from 2004 to 2012, the average incidence rate per 100,000 person-years was 32.7 (95% CI 31.5, 34.0). After adjustment for age and sex, the estimated change per year was 1.8% for 1989–1996 (95% CI −0.07, 3.6; p = 0.059), 3.4% for 1996–2004 (95% CI 2.2, 4.7; p