Autism spectrum disorders: How prevalent are they, really?

When Contemporary Pediatrics published an article on the need for early autism screening in October 2005, the authors gave a figure for the prevalence of autistic spectrum disorder (ASD) as 1 in 500. That figure was promptly challenged in a letter to the editor from Raymond Gallup, a parent advocate and founder of the Autism Autoimmunity Project. The "actual statistic," wrote Reader Gallup, is 1 in 166-a considerably more alarming number. Actually, as the authors' reply indicated, prevalence estimates current at that time ranged from a low of 1 in 500 to a high of 1 in 166-and that variability was a sure indication of how much remained unknown about this developmental disorder.

Now the CDC has released new data on findings on 8-year-old children living in 14 communities surveyed in 2002. The new data show ASD rates in the 14 sites that range from 1 in 303 to 1 in 94, which averages out to an ASD prevalence rate of one in every 152 children (Prevalence of Autism Spectrum Disorders: Autism and Developmental Disabilities Monitoring Network, 14 sites, US 2002. MMWR Surveil Sum 2007;56[SS-1])-an even higher rate than earlier studies had revealed.

The new study identified children with ASD through screening and abstraction of evaluation records at health facilities for all 14 sites, and from psychoeducational evaluations for special education services for 10 of the sites. Children whose records documented behaviors consistent with the Diagnostic and Statistical Manual of Mental Disorders criteria for autistic disorder, pervasive developmental disorder not otherwise specified, or Asperger's syndrome were classified as having ASDs. The studies "do not provide a national estimate, but they do confirm that ASD in the areas surveyed are more common than previously thought," says Dr. Marshalyn Yeargin-Allsop, chief of the CDC's autism program. Prevalence studies like this one provide a better sense of the seriousness of the problem, but do not shed light on etiology. For that, parents and physicians will have to wait for data from another ongoing, multi-state CDC study, designed to identify risk factors for ASD and other developmental disabilities.