CDC: Rise in Autism Is (at Least) Partly due to Increased Recognition, Documentation

From 2002 to 2006, the prevalence of autism spectrum disorders (ASDs) increased significantly among 8-year-old American boys and girls.* This conclusion is based on a newly published, retrospective review from the CDC's Autism and Developmental Disabilities Monitoring (ADDM) Network. The CDC investigators ascribe the increased prevalence of ASDs to improved recognition and documentation, but they cannot dismiss a concomitant "true" increase in ASDs.

On the basis of an examination of health and education records at 11 US sites participating in the ADDM Network, the average prevalence of ASDs among 8-year-olds in 2006 was 9.0 per 1000 children (range, 4.2-12.1), or nearly 1%. Among the 10 US sites that provided data for both 2002 and 2006, the overall prevalence of ASDs increased significantly, by 57%. This finding contrasts with a comparison of data from 2000 and 2002, which revealed no significant increase in the overall prevalence of ASDs.

Below are the tabulated prevalence values for ASD at the 10 common sites, stratified by sex, ethnicity, and IQ. These data show consistent across-the-board increases in ASD among the assessed pediatric subgroups.

The CDC investigators note that the average prevalence of ASDs was higher at sites that had access to health and education records (10.0) than at sites with only health records (7.5). This observation suggests that more opportunities for ASD documentation increase the prevalence of the condition (artificially). Investigators also found that, generally, ASDs were recognized at younger ages in 2006 than in 2002. (And if I'm correctly reading the CDC data, they indicate that significantly more children with below-normal IQs are being classified as having ASDs—a phenomenon that may also explain an increased prevalence of ASDs.)

Most of the children identified as having ASDs in 2006 (70%-90%) displayed developmental problems (eg, language delay) before the age of 3 years; however, the average age at diagnosis was considerably later, at about 4½ years (suggesting lost time for crucial behavioral interventions). In 2006 assessment, most 8-year-olds with ASDs (76%-96%) were receiving special education through public-school programs, under a wide variety of rationales (eg, autism, emotional disturbance, learning disability, language impairment, etc).

The CDC advises that the ADDM Network surveillance sites were selected "on the basis of their ability to conduct active ASD records-based surveillance," and were not intended to be a nationally representative sample. However, the Network accessed the records of more than 300,000 children, representing nearly 8% of all 8-year-olds in the United States.

Data supporting the approximate 1% prevalence of ASDs include a 2007 parent survey and several contemporary international studies, says the CDC. 

* ASDs are defined on the basis of documented behaviors consistent with the DSM-IV-TR criteria for autistic disorder; pervasive development disorder, not otherwise specified; and Asperger disorder. The age of 8 years is identified as a "reasonable index age at which to monitor peak prevalence for ASDs." ASD symptoms are usually observed before the age of 3 years.

** The whopping increased prevalence of ASDs in Hispanic children is attributed to the increase in the Hispanic population overall and a prevalence increase of 144% in Arizona. The other Network sites did not reveal an increased prevalence of ASD among Hispanic children.