Autism Spectrum Disorders on the Rise: Inside the CDC Report

More children than ever before are being diagnosed with autism spectrum disorders (ASD). The Centers for Disease Control and Prevention (CDC) has released the most comprehensive U.S. investigation of autism prevalence to date. The current CDC report, Prevalence of Autism Spectrum Disorders — Autism and Developmental Disabilities Monitoring Network, 14 Sites, United States, 2008, provides updated ASD prevalence estimates from the 2008 surveillance year, representing 14 Autism and Developmental Disabilities Monitoring (ADDM) community sites in the United States - Alabama, Arizona, Arkansas, Colorado, Florida, Georgia, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah and Wisconsin. In addition to prevalence estimates, characteristics of the population of children with ASD are described, as well as detailed comparisons of the 2008 surveillance year findings with those for the 2002 and 2006 surveillance years. Briefly, a child is included as meeting the surveillance case definition for an ASD if he or she displays behaviors (as described on a comprehensive evaluation completed by a qualified professional) consistent with the American Psychiatric Association's Diagnostic and Statistical Manual-IV, Text Revision (DSM-IV-TR) diagnostic criteria for any of the following conditions: Autistic Disorder; Pervasive Developmental Disorder–Not Otherwise Specified (PDD-NOS, including Atypical Autism); or Asperger Disorder.

The following are salient points culled from the full CDC report.

The current data confirm that the estimated prevalence of ASD identified in the ADDM network surveillance populations continues to increase. For 2008, the overall estimated prevalence of ASDs among the 14 ADDM sites was 11.3 per 1,000 (one in 88) children aged 8 years who were living in these communities during 2008. However, overall ASD prevalence estimates varied widely across all 14 sites (range: 4.8–21.2 per 1,000 children aged 8 years). Note: Because the ADDM Network sites do not make up a nationally representative sample, these combined prevalence estimates should NOT be generalized to the United States as a whole. The surveillance areas were not selected to be representative of the United States, nor were they selected to be representative of the states in which they are located.

Comparison of 2008 findings with those for earlier surveillance years indicated an increase in estimated ASD prevalence of 23% when the 2008 data were compared with the data for 2006 (from 9.0 per 1,000 children aged 8 years in 2006 to 11.0 in 2008 for the sites that provided data for both surveillance years). There was an estimated increase of 78% when the 2008 data were compared with the data for 2002 (from 6.4 per 1,000 children aged 8 years in 2002 to 11.4 in 2008 for the sites that provided data for both surveillance years).

Approximately one in 54 boys and one in 252 girls living in the ADDM Network communities were identified as having ASDs. ASD prevalence estimates were significantly (p<0.01) higher among boys than among girls in all 14 ADDM sites.

Changes in estimated ASD prevalence during 2006–2008 also varied by race within individual ADDM sites and when combining data from all sites. While ASD prevalence estimates in the overall population increased 23% for the 2-year period 2006–2008, and 78% during the 6-year period 2002–2008, the largest increases over time were noted among Hispanic children and non-Hispanic black children. The combined estimates indicated a 16% increase in ASD prevalence among non-Hispanic white children, a 42% increase among non-Hispanic black children, and a 29% increase among Hispanic children. It should be noted that better identification in these specific groups appears to explain only part of the overall increase.

Data on intellectual ability are reported for the seven sites having information available for at least 70% of children who met the ASD case definition. When data from these sites were combined, 38% of children with ASD were classified in the range of intellectual disability (e.g., IQ ≤70 or an examiner's statement of intellectual disability), 24% in the borderline range (IQ 71–85), and 38% had IQ scores >85 or an examiner's statement of average or above-average intellectual ability. Comparing IQ test data available in both the 2006 and 2008 surveillance years, the estimated prevalence of ASD with intellectual disability increased 12% on average, while the prevalence of ASD with borderline intellectual ability increased 22%, and the prevalence of ASD with average or above-average intellectual ability increased 13%.

The estimated ASD prevalence continues to rise in most ADDM Network sites, reflecting an important public health concern in the United States and underscoring the need for continued resources to identify potential risk factors and to provide essential supports for persons with ASD and their families. Unfortunately, many children with ASD do not receive a diagnosis until they reach preschool or kindergarten age, missing opportunities for earlier therapies that potentially could improve communication and socialization while these skills are developing. CDC is partnering with other federal and private partners in a coordinated response to identify risk factors for ASDs and to meet the needs of persons with ASDs and their families. Additional information is available at http://www.cdc.gov/autism.

The CDC cautions that data provided in this report are subject to some limitations. For example, while increases in awareness and access to services have improved the ability of the ADDM Network to identify children with ASD over time and likely contributes to the increase in estimated prevalence, the proportion of the increase attributable to changes in case ascertainment or attributable to a true increase in prevalence of ASD symptoms cannot be determined. Ongoing monitoring is an important tool to learn why more children are being identified with ASD and can provide important clues in the search for risk factors. 

The CDC report concludes that although multiple factors influence the identification of children with ASD and differences in prevalence estimates across sites, the data provided in this report indicate the need for further exploration of possible associations between overall ASD prevalence and improved identification among children without intellectual disability, children in all racial/ethnic populations, and both males and females, including potential interactions between these factors. 

The complete report is available at

http://www.cdc.gov/mmwr/preview/mmwrhtml/ss6103a1.htm?s_cid=ss6103a1_w

Lee A. Wilkinson, PhD, CCBT, NCSP is author of the award-winning book, A Best Practice Guide to Assessment and Intervention for Autism and Asperger Syndrome in Schools, published by Jessica Kingsley Publishers.

 © Lee A. Wilkinson, PhD