Regular peaks and troughs in the Australian incidence of childhood type 1 diabetes mellitus (2000–2011)

Aims/hypothesis: The aim of this study was to determine the incidence and incidence rate trends for type 1 diabetes mellitus in children aged 0–14 years, Australia-wide, from 2000 to 2011. Methods: Cases of type 1 diabetes mellitus diagnosed in 0- to 14-year-olds were identified from the National (insulin-treated) Diabetes Register, with a 97% ascertainment rate. Annual age-standardised, sex- and age-specific incidences were calculated and Poisson regression was used to analyse the incidence by calendar year, sex and age at diagnosis. Non-linear temporal trends were analysed using sine and cosine functions applied to Poisson regression models for 3, 4, 5, 6 and 7 year cycles, and the Akaike information criterion was used to assess goodness of fit. Results: A total of 11,575 cases (6,049 boys and 5,526 girls) of childhood type 1 diabetes mellitus were registered between 2000 and 2011, giving a mean incidence of 23.6 per 100,000 person-years (95% CI 23.2, 24.0). The mean incidence was 4.9% (95% CI 1.1%, 8.8%) higher in boys than in girls. Compared with 0- to 4-year-olds, the mean incidence was 65% higher in 5- to 9-year-olds and 208% higher in 10- to 14-year-olds. A 5 year cyclical variation in incidence was observed overall, in both sexes and in all age groups. An average annual increase in incidence was observed only in the 10- to 14-year-old age group (increase of 1.2% per year [95% CI 0.4%, 2.1%]). Conclusions/interpretation: A sinusoidal pattern was observed in the incidence rate trend of childhood type 1 diabetes mellitus in Australia. The 5-yearly peaks and troughs in incidence rate trends observed Australia-wide corroborate findings previously reported for Western Australia and require further investigation.