Objective: To determine the epidemiology of type 1 diabetes in children in Philadelphia from 1990 to 1994, and to identify whether an epidemic occurred during that time period.
Research design and methods: This is a descriptive epidemiological study using a retrospective population-based registry in Philadelphia, PA, a city with large white, African-American, and Hispanic (Puerto Rican) populations. All hospitals in Philadelphia that admit children were identified. All charts meeting the following criteria were reviewed: 1) newly diagnosed type 1 diabetes, 2) children 0-14 years of age, 3) children residing in Philadelphia at the time of diagnosis, and 4) those diagnosed from 1 January 1990 to 31 December 1994. Standard type 1 diabetes registry data were abstracted from the charts. Ascertainment of the completeness of the hospital registry was validated by data from the Philadelphia School District. Communicable disease records were reviewed to identify epidemics from 1987 to 1995.
Results: A total of 209 cases were identified, and the combined hospital and school registry was determined to be 96% complete. The overall age-adjusted incidence rate in Philadelphia was 13.3/100,000/year. The highest rate by race continues to be in the Hispanic population (15.5). The incidence in African-American children has increased markedly (12.8), particularly in the 10- to 14-year age-group (22.9). An epidemic of type 1 diabetes occurred from January to June 1993, approximately 2 years after a measles epidemic in Philadelphia.
Conclusions: The overall incidence of type 1 diabetes in Philadelphia is similar to other U.S. registries. The incidence in the Hispanic population continues to be among the highest of any U.S. ethnic group. The marked increase in incidence in the African-American population may be due in part to misclassification of cases actually having type 2 diabetes. The 1993 epidemic may have been due to beta-cell autoimmunity triggered by the measles virus.