Rising Incidence of Type 1 Diabetes in Germany: 12-Year trend analysis in children 0–14 years of age Free

Epidemiological studies from all parts of the world have reported increases in incidence of type 1 diabetes (1). In a 6-year population-based study that concluded in 1993 and was published in 1997, the incidence of type 1 diabetes in German children 0–14 years of age was reported to be 11.6 per 100,000 children a year (95% CI 10.9–12.2) (2). Using the Baden-Wuerttemberg (BW) incidence registry, data regarding 2,525 children with diabetes were analyzed over a 12-year period. Our objective was to determine the most recent trends in the incidence of childhood diabetes in Germany.

BW is a federal state in Southwest Germany. The total number of inhabitants was 10.4 million at the time of this research, and 1.8 million (16.9%) were younger than 15 years of age. This corresponds to 13.3% of the total child population in Germany. These population data were drawn from a national census in 1987 and the official yearly update thereafter.

Patients were registered according to European Diabetes (EURODIAB) Study criteria (3). They were included only if insulin treatment had begun before the 15th birthday and if the manifestation of disease occurred between 1 January 1987 and 31 December 1998.

All 31 pediatric departments in BW and 1 diabetes center participated in the study. Registration was done retrospectively for the time period between 1 January 1987 and 30 June 1997 and prospectively for the time period between 1 July 1997 and 31 December 1998. For the earlier time period, 2,121 hospital records were the primary data source. For the latter time period, 404 patients were registered prospectively. A separate secondary source of data was provided by a questionnaire distributed among members of the Diabetic Patients’ Association (Deutscher Diabetiker Bund). The degree of ascertainment was calculated according to the capture-mark-recapture method (4) and resulted in 97.0% for the primary data source and 97.2% when both data sources were combined.

Sex and age standardization was done according to EURODIAB criteria. The 95% CI limits were calculated for all incidence rates assuming a Poisson distribution, or if n was higher than 100, assuming a normal distribution. Trend analysis was performed using the linear regression model, because this mathematical model seems to best describe the incidence development as a function of time. The correlation coefficient is given as R², and the probability was calculated using Fisher’s test (represented as P).

The mean age and sex standardized incidence rate over 12 years was found to be 12.9 per 100,000 children a year (95% CI 12.4–13.4). The absolute increase in incidence was calculated with 0.44 per 100,000 children a year (0.26–0.62). This corresponds to an annual increase of 3.6%. Compared with the incidence in 1987, the overall increase in incidence over 12 years was 47.0%.

The mean incidence from 1987 to 1998 (12.9 per 100,000) was higher than that previously reported by the German Democratic Republic (7.4 per 100,000) (5) and by BW (2) in the early 1990s. For the children <15 years of age, incidence peaks up to 15.6 per 100,000 (Fig. 1) have not previously been seen in this region. In comparison with our earlier published incidence rate of 11.6 per 100,000 children a year (95% CI 10.9–12.2) from 1987 to 1993 in the same region, the incidence rate of 14.3 (13.5–15.0) from 1993 to 1998 was higher and clearly indicates the increasing incidence rate in German children during the last decade.

The increase of 3.6% per year in BW is higher than the international mean (2.5–3.0%), but similar numbers have been reported in Oxford, U.K. (3.7%), and in France (3.9%) (1).

As in most European countries, the increase in incidence cannot be easily explained. Whether environmental or genetic factors play a predominant role is a matter of controversial debate (6,7). Data on the incidence in the age-group ≥15 years of age are not available for our population. Thus, the observed trend may reflect a transition of the age at onset from children ≥15 years of age to children <15 years of age.

Knowing that a linear model may even underestimate the increase in incidence (1), one can make predictions by extrapolating the curve. Our calculations predict a doubling of the incidence rate within 20 years, reaching 24.7 per 100,000 children a year in the year 2020.