The CDC estimates that about one in 68 US children has autism spectrum disorder, according to findings published in the March 28 issue of Morbidity and Mortality Weekly Report Surveillance Summaries. This prevalence is a 30% increase from the CDC’s estimate of one in 88 children using 2008 data.
The findings also show that autism spectrum disorder continues to be more prevalent in boys than in girls: one in 42 boys had autism spectrum disorder in the latest report, compared with one in 189 girls.
The increased prevalence could be attributed to improved clinician identification of autism, a growing number of autistic children with average to above-average intellectual ability, or a combination of both factors, said Coleen Boyle, PhD, Director of the CDC’s National Center on Birth Defects and Developmental Disabilities (NCBDDD).
The CDC analyzed 2010 data collected by its Autism and Developmental Disabilities Monitoring (ADDM) Network, which provides population-based estimates of autism spectrum disorder prevalence in children age 8 at 11 sites in the United States based on records from community sources that diagnose and provide services to children with developmental disabilities.
Of the 11 sites studied, seven had information available on the intellectual ability of at least 70% of children with autism spectrum disorder. Of the 3,604 children for whom data were available, 31% were classified as having intellectual disability (IQ of 70 or lower), 23% were considered borderline (IQ = 71 to 85), and 46% had IQ scores of greater than 85, considered average or above average intellectual ability.
“We recognize now that autism is a spectrum, no longer limited to the severely affected,” said Marshalyn Yeargin-Allsopp, MD, Chief of the Developmental Disabilities branch of NCBDDD. “There are children with higher IQs being diagnosed who may not even be receiving special education services, and the numbers may reflect that.”
Non-Hispanic white children were 30% more likely to be diagnosed with autism spectrum disorder than were non-Hispanic black children and about 50% more likely to be diagnosed with autism spectrum disorder than were Hispanic children.
Dr. Boyle stressed the importance of early screening and identification of autism spectrum disorder in children (it can be diagnosed by the time a child reaches age 2) and urged parents to take action if a child shows any signs of developmental delays.
“Community leaders, health professionals, educators, and childcare providers should use these data to ensure that children with autism spectrum disorder are identified as early as possible and connected to the services they need,” said Dr. Boyle.
To help promote early intervention in autism spectrum disorder, the CDC will be launching an awareness initiative called “Birth to Five, Watch Me Thrive,” which aims to provide parents, teachers, and community members with information and resources about developmental milestones and screening for autism.
“Most children with autism are not diagnosed until after age 4,” said Dr. Boyle. “The CDC will continue to promote early identification and research. The earlier a child is identified and connected with services, the better.”
The CDC cited several limitations to the report. First, the surveillance sites were not selected to be representative of the entire United States. Second, population denominators used for this report were based on the 2010 decennial census. Comparisons with previous ADDM findings thus should be interpreted with caution because ADDM reports from nondecennial surveillance years are likely influenced by greater error in the population denominators used for those previous surveillance years, which were based on postcensus estimates. Third, three of the nine sites with access to review children’s education records did not receive permission to do so in all school districts within the site’s overall surveillance area. Fourth, findings that address intellectual ability might not be generalizable to all ADDM sites. Finally, race and ethnicity are presented in broad terms and should not be interpreted as generalizable to all persons within those categories.
—Madhu Rajaraman