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The Prevalence of Autism Spectrum Disorders

Are they really on the rise?

Studies during the past decade have indicated an increase in the number of children diagnosed with autism. A recent report from the CDC is the largest to date on the prevalence of autism spectrum disorders (ASDs) among U.S. children.

In a population-based study in 2000, 14 sites in different states participated in a surveillance program to identify 8-year-old children with ASDs. Investigators reviewed medical records and psychoeducational evaluations for special education services to identify behaviors consistent with the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) criteria for autism, pervasive developmental disorder, or Asperger syndrome.

Among a population of more than 407,500 children, 2685 (0.66%) had ASDs. The prevalence of ASDs ranged from 3.3 to 10.6 per 1000 children (most sites ranged from 5.2 to 7.6); the overall mean prevalence was 6.6 per 1000 children (1/152 children). Five sites identified a significantly higher prevalence of ASDs among non-Hispanic white children compared with non-Hispanic black children. The male-to-female ratio at the various sites ranged from 3.4 to 6.5 boys to 1 girl, and the median age of earliest documented ASD ranged from 49 to 66 months. Among the six sites with prevalence data for both 2000 and 2002, the prevalence of ASDs remained stable in four and was higher in two.

Comment: Despite this study’s many strengths (use of multiple sites in different states, two sources of data on behavior, standardized review of records with documented interrater reliability, and use of DSM-IV-TR diagnostic criteria), it lacks clinical reassessment of children to determine current case status and data on ASD subtypes.

The reported increase in ASD prevalence from 1/1000 in the early 1990s to 1/152 in 2002 has generated much concern. But is this prevalence actually increasing among children? Several potential reasons might explain the apparent increase. The clinical definition of autism has expanded to include a wider spectrum of behaviors and developmental criteria. Clinicians, teachers, and parents are more aware of autistic behaviors. Children with coexisting mental retardation and autism may now have a primary diagnosis of autism rather than mental retardation. Finally, more services are available in schools and in the community. My hunch is that these factors play a large role in the increase in ASD prevalence, perhaps in some communities more than others.

— Martin T. Stein, MD

Published in Journal Watch Pediatrics and Adolescent Medicine March 21, 2007

Citation(s):

Centers for Disease Control and Prevention (CDC). Prevalence of autism spectrum disorders — Autism and developmental disabilities monitoring network, 14 sites, United States, 2002. MMWR Surveill Summ 2007 Feb 9; 56:12-28.

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