DRAMATIC INCREASE IN INCIDENCE OF INSULIN-DEPENDENT DIABETES-MELLITUSIN WESTERN-AUSTRALIA

Objectives: To document and suggest possible reasons for a dramatic in crease in the incidence of insulin dependent diabetes mellitus (IDDM) in Western Australia in 1992. Patients: Children aged 0-14 years with IDDM diagnosed in Western Australia from 1985 to 1992 inclusive. Desig n: A population-based register in Western Australia, using name-identi fied data from two separate ascertainment sources, provided numerator data. Denominator data were estimated from census figures collected in 1986 and 1991 by the Australian Bureau of Statistics. The completenes s of case ascertainment was estimated by the capture-recapture method. Results: Case ascertainment for 1985-1992 was estimated as 99.6% comp lete. Between 1985 and 1991 the incidence of IDDM in the 0-14 year age group varied between 11.8 and 15.5 per 100 000 person-years without a significant increase. In 1992, however, based on the previous seven y ears, 52 cases would have been expected but 84 cases were observed, an incidence of 22.2 per 100 000 person-years. The increase in incidence occurred across all age groups and in both sexes. Place of residence at diagnosis, the prevalence of islet cell antibody positivity at diag nosis and the proportion of new cases with a first degree relative wit h IDDM were no different in 1992 than in preceding years. Conclusion: This is the first report of a significant increase in the incidence of IDDM in Australia. It appears to be a period, rather than a cohort, e ffect and provides further evidence for environmental antigens as dise ase triggers.