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Ann Epidemiol. 2009 Nov;19(11):808-14. doi: 10.1016/j.annepidem.2009.04.005. Epub 2009 Jun 21.

Autism spectrum disorders in preschool-aged children: prevalence and comparison to a school-aged population.

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  • 1Department of Biostatistics, Bioinformatics, and Epidemiology, Medical University of South Carolina, Charleston, SC 29425-8350, USA.



The purpose of this study was to determine the prevalence and case characteristics of children with autism spectrum disorders (ASDs) among 4-year-olds and to compare findings to previous prevalence estimates for 8-year-olds in the same geographic area.


South Carolina (SC) has been a participant in the Centers for Disease Control and Prevention's active, population-based, multiple-site ASD surveillance network for 8-year-olds since 2000. The 8-year-old methodology, designed to identify children both with and without prior diagnosis, was applied in SC with modification to include information sources for younger children.


The ASD prevalence among 4-year-olds in 2006 was 8.0 per 1000 (95% confidence interval [CI], 6.1-9.9), or 1 in 125. In comparison, ASD prevalence among 8-year-olds in the same geographic area was 7.6 (95% CI, 5.7-9.5) in 2000 and 7.0 (95% CI 5.1-8.9) in 2002. Developmental concerns were documented at earlier ages across time, and while most cases received services, only 20% to 29% received services specific to ASD.


Findings should provide useful information for the planning of health/education policies and early intervention strategies for ASD.

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