Irva Hertz-Picciotto1, Lora Delwiche. 1. Department of Public Health Sciences, University of California, Davis, California 95616, USA. ihp@ucdavis.edu
Abstract
BACKGROUND: Autism prevalence in California, based on individuals eligible for state-funded services, rose throughout the 1990s. The extent to which this trend is explained by changes in age at diagnosis or inclusion of milder cases has not been previously evaluated. METHODS: Autism cases were identified from 1990 through 2006 in databases of the California Department of Developmental Services, which coordinates services for individuals with specific developmental disorders. The main outcomes were population incident cases younger than age 10 years for each quarter, cumulative incidence by age and birth year, age-specific incidence rates stratified by birth year, and proportions of diagnoses by age across birth years. RESULTS: Autism incidence in children rose throughout the period. Cumulative incidence to 5 years of age per 10,000 births rose consistently from 6.2 for 1990 births to 42.5 for 2001 births. Age-specific incidence rates increased most steeply for 2- and 3-year olds. The proportion diagnosed by age 5 years increased only slightly, from 54% for 1990 births to 61% for 1996 births. Changing age at diagnosis can explain a 12% increase, and inclusion of milder cases, a 56% increase. CONCLUSIONS: Autism incidence in California shows no sign yet of plateauing. Younger ages at diagnosis, differential migration, changes in diagnostic criteria, and inclusion of milder cases do not fully explain the observed increases. Other artifacts have yet to be quantified, and as a result, the extent to which the continued rise represents a true increase in the occurrence of autism remains unclear.
BACKGROUND:Autism prevalence in California, based on individuals eligible for state-funded services, rose throughout the 1990s. The extent to which this trend is explained by changes in age at diagnosis or inclusion of milder cases has not been previously evaluated. METHODS:Autism cases were identified from 1990 through 2006 in databases of the California Department of Developmental Services, which coordinates services for individuals with specific developmental disorders. The main outcomes were population incident cases younger than age 10 years for each quarter, cumulative incidence by age and birth year, age-specific incidence rates stratified by birth year, and proportions of diagnoses by age across birth years. RESULTS:Autism incidence in children rose throughout the period. Cumulative incidence to 5 years of age per 10,000 births rose consistently from 6.2 for 1990 births to 42.5 for 2001 births. Age-specific incidence rates increased most steeply for 2- and 3-year olds. The proportion diagnosed by age 5 years increased only slightly, from 54% for 1990 births to 61% for 1996 births. Changing age at diagnosis can explain a 12% increase, and inclusion of milder cases, a 56% increase. CONCLUSIONS:Autism incidence in California shows no sign yet of plateauing. Younger ages at diagnosis, differential migration, changes in diagnostic criteria, and inclusion of milder cases do not fully explain the observed increases. Other artifacts have yet to be quantified, and as a result, the extent to which the continued rise represents a true increase in the occurrence of autism remains unclear.
Authors: Irva Hertz-Picciotto; Lisa A Croen; Robin Hansen; Carrie R Jones; Judy van de Water; Isaac N Pessah Journal: Environ Health Perspect Date: 2006-07 Impact factor: 9.031
Authors: Rachel Nonkin Avchen; Lisa D Wiggins; Owen Devine; Kim Van Naarden Braun; Catherine Rice; Nancy C Hobson; Diana Schendel; Marshalyn Yeargin-Allsopp Journal: J Autism Dev Disord Date: 2011-02
Authors: Judith K Grether; Yinge Qian; Mary S Croughan; Yvonne W Wu; Michael Schembri; Loretta Camarano; Lisa A Croen Journal: J Autism Dev Disord Date: 2013-03
Authors: Laura A Schieve; Catherine Rice; Owen Devine; Matthew J Maenner; Li-Ching Lee; Robert Fitzgerald; Martha S Wingate; Diana Schendel; Sydney Pettygrove; Kim van Naarden Braun; Maureen Durkin Journal: Ann Epidemiol Date: 2011-10-13 Impact factor: 3.797