Epidemiology of IDDM in Switzerland: Increasing incidence rate and rural-urban differences in Swiss men born 1948-1972

Abstract

OBJECTIVE To determine the incidence of insulin-dependent diabetes mellitus (IDDM) in Switzerland by undertaking a retrospective analysis of the registry of the Swiss army, which contains updated medical files for all male Swiss citizens. Nationwide data for IDDM epidemiology have not been available in Switzerland. RESEARCH DESIGN AND METHODS Every male Swiss citizen is obliged to enlist in the Swiss military service at 19 years of age, when a personal, continuously updated medical file is established. Diabetes is an exclusion condition for military service and is clearly marked in the file. A total number of 514,747 files, corresponding to birth year cohorts 1948-1950, 1955-1957, 1962-1964, and 1970-1972, have been manually checked for the diagnosis of IDDM. RESULTS IDDM was identified in 926 cases in the four groups of three age-cohorts. The incidence at ≤15 years (per 100,000/year) was 4.5 in the age cohorts 1948-1950 and 7.2 in the age cohorts 1970-1972 (P < 0.005). An additive age-cohort Poisson regression model fits the nationwide incidences adequately, neither a period effect nor age X cohort interactions being required. In the oldest age cohorts, the age-specific incidence of IDDM was calculated up to the age of 43 and was ∼7/ 100,000/year in men between 20 and 40. In these age cohorts, we found an ∼50% higher risk to develop IDDM at age ≤19 for men living in an urban region and a significantly (P < 0.005) increased incidence between 20 and 40 years in rural regions compared with urban regions. CONCLUSIONS The incidence of IDDM in Switzerland is comparable to other countries in central Europe and has been increasing in the last 20 years. This is in accordance to most recent epidemiological studies worldwide. In addition, the data suggest exogenous factors inducing IDDM at a younger age in urban regions.