Elsevier

Annals of Epidemiology

Volume 19, Issue 11, November 2009, Pages 808-814
Annals of Epidemiology

Autism Spectrum Disorders in Preschool-Aged Children: Prevalence and Comparison to a School-Aged Population

https://doi.org/10.1016/j.annepidem.2009.04.005Get rights and content

Purpose

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.

Methods

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.

Results

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.

Conclusions

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

Introduction

Autism spectrum disorders (ASDs) are a group of developmental disabilities characterized by pervasive deficits in socialization and communication, as well as unusual behaviors or interests (1). The most recent estimates of ASD prevalence among 8-year-old children in the United States are from the Centers for Disease Control and Prevention's (CDC) Autism Developmental Disabilities and Monitoring (ADDM) Network and range from 3.3 to 10.6 per 1,000 children across the 14 Network sites, with an overall mean prevalence of 6.6 per 1000 (2). Based on other ADDM Network findings as well as a similar surveillance program among 8-year-old children in the metropolitan Atlanta area, this estimate places ASD as the second most prevalent serious developmental disability behind intellectual disability (intellectual disability, 12 per 1000 (3); cerebral palsy, 3.3 per 1000 (4); hearing loss and visual impairment, 2.1 per 1000 each (3)).

The purpose of this study was to determine the prevalence and case characteristics of children with ASD among a population of 4-year-olds and to compare findings with previous surveillance of 8-year-olds in the same geographic area. In addition to providing population-based information on the frequency of ASD among younger children, findings should be useful to program planners and decision makers in developing health/education policies and early intervention strategies.

Section snippets

Methods

South Carolina (SC) has been a member of the ADDM Network since its inception, conducting surveillance using standard ADDM Network methodology 2, 5, 6 among children aged 8 years across multiple birth-year cohorts. Description and results from SC's surveillance of 8-year-old children have been previously published 2, 6, 7. The surveillance of 4-year-old children reported in this study used the same methodology as these previous studies, modified to include state-specific sources for younger

ASD Prevalence among 4-year-old Children and Case Characteristics

In 2006, in the three-county subregion of the SC ADDM surveillance area, the total prevalence of ASDs in children aged 4 years was 8.0 per 1000 (95% confidence interval [CI], 6.1–9.9; 65 confirmed cases in a population of 4-year-olds numbering 8,156). Among males the prevalence was 13.0 per 1,000 (95% CI, 9.5–16.4); among females, the prevalence was 2.8 per 1000 (95% CI, 1.1–4.4), resulting in a male-female ratio of 4.7 to 1. The white-to-black prevalence ratio was 1.5 to 1 (36 cases missing

Discussion

Results of this study indicate that, for the region studied, the prevalence of ASDs among children aged 4 years in 2006 was 8.0 per 1000, with a male-to-female ratio of 4.7 to 1. Of the 66% of confirmed cases with cognitive functioning data, 44% had an IQ score of 70 or above (7% unspecified severity). Aside from core diagnostic criteria, characteristics most commonly reported were hyperactivity or attention problems (72%), odd response to sensory stimuli (68%), temper tantrums (59%),

Conclusion

The surveillance of ASDs at an earlier, preschool age provides valuable information for the subsequent planning, implementation, and evaluation of resources and interventions for children with ASDs. The prevalence of ASDs among 4-year-olds in 2006 was 8 per 1000, or 1 in 125. This is somewhat higher, but within 95% confidence limits, of the prevalence for 8-year-olds in the same geographic area in the years 2000 and 2002. While most of these children were receiving special education services, a

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