The estimated prevalence of autism spectrum disorders at sites across the country that are tracking prevalence rates among 8-year-old children increased by 23% between 2006 and 2008, according to a report published March 29 by the Centers for Disease Control and Prevention.

An estimated 1 of every 88 children had an ASD in 2008 at the 14 sites, which are part of the Autism and Developmental Disabilities Monitoring (ADDM) Network, an active surveillance system established by the CDC in 2000 to collect data on ASDs and other developmental disabilities in the United States. That represents a 23% increase from 2006, when 1 in 110 children had an ASD, and almost an 80% increase from 2002.

In 2008, prevalence was five times more common in boys, with 1 of every 54 boys affected by an ASD, compared with 1 of every 252 girls, another finding of the study that is included in the report, published in the March 30 issue of Morbidity and Mortality Weekly Report (MMWR 2012;61:1-19).

The study evaluated data from 14 sites in the United States in 2008, and compared the results with those of previous years. Cases are based on the presence of ASD symptoms at any time from birth through the end of the year a child turns 8 (as described in a child’s education and health records, not from parent or professional reports), that meet DSM-IV-TR diagnostic criteria for autistic disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS, including atypical autism), or Asperger’s disorder.

“Some of the increase is due to the way children are identified, diagnosed, and served in our local communities, although how much is due to these factors is not known,” Coleen A. Boyle, Ph.D., director of the CDC’s National Center on Birth Defects and Developmental Disabilities, said during a telebriefing held to announce the report’s results. She said that research on the risk factors and causes of autism needs to be continued, and pointed out that tracking the prevalence also helps identify potential risk factors and helps guide research on the potential causes of autism.

The median age at diagnosis was 4 years among those tracked in 2008, compared with 4.5 years in 2006, she said. The number of children diagnosed by age 3 years increased from 12% of those born in 1994, to 18% of those born in 2000, according to the report.

During the briefing, Dr. Susan L. Hyman, chairperson of the Autism Subcommittee of the American Academy of Pediatrics (AAP), said that although the age of diagnosis for the children in 2008 was younger than in previous reports, “it’s not early enough.” She referred to the AAP recommendation that all children be screened for autism at 18 and 24 months, so that children with autism can be identified and referred for appropriate treatment and services sooner.

“While there are a number of potential reasons for this increase, the nature of the sites where the data have been collected support that the notion that these trends are not just explained by the broadened definition of autism in the change from the DSM-III-R to the DSM-IV in 1994, or to ascertainment,” Dr. Robert L. Hendren, director of child and adolescent psychiatry at the University of California, San Francisco, said in an interview. What continues to be frightening about the increase is that it is unexplained, he said, adding “we see increases in obesity and diabetes, and we have good theories about why. We don’t for autism.”

Dr. Hendren, professor and vice chair of the department of psychiatry at UCSF, said more research that looks at the gene-environment interaction etiology of autism is needed. “And we need stronger, broadly available targeted treatments for autism that are accessed early and broadly. We also need to help the growing adolescent and adult population with these disorders to live as fulfilling a life as possible.”

Dr. Paul H. Lipkin, associate professor of pediatrics at Johns Hopkins University, Baltimore, said, “The rise is likely related in part to improved recognition to the signs and symptoms of [autism spectrum disorder] by professionals, parents, and the general public over the past decade.

“It remains unclear whether there are unrecognized biological or environmental factors affecting early childhood development and adding to this increased prevalence,” he said in an interview.

“By looking at 8-year-old children, the CDC is assuring that the identified children are those with ongoing special health care and educational needs, rather than a group whose symptoms may remit,” said Dr. Lipkin, who also is the director of the Center for Development and Learning at the Kennedy Krieger Institute in Baltimore.*

In addition to sex differences, the report found wide variations in prevalence estimates by sites, and by racial and ethnic groups. For example, the prevalence of ASDs ranged from 1 of every 210 children in Alabama to 1 of every 47 children in Utah. And at all the sites, the estimated prevalence in non-Hispanic white children was significantly higher than the prevalence in non-Hispanic black children and Hispanic children overall, with one exception: In Florida, the prevalence was significantly higher in Hispanic children than in non-Hispanic white or non-Hispanic black children.

The estimated prevalence of ASD was also significantly higher at sites where there was access to education sources, compared with the sites that only had health sources to help identify cases.

In 2008, the 14 sites covered an area that included a total of about 337,000 children aged 8 years, representing about 8% of the 8-year-olds in the United States. Although the report notes that the ADDM sites are not nationally representative and the results should not be generalized to the United States overall, Dr. Boyle said these trends are comparable to the prevalence estimates in other national surveys.

The ADDM sites are in Alabama, Arizona, Arkansas, Colorado, Florida, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah, West Virginia, and Wisconsin.

No conflicts of interest were reported.

More information about autism, including a link to the report, is available from the CDC.