CDC: National autism rates 30% higher than previous estimates

The number of US children diagnosed with autism spectrum disorders was 30% higher than previous estimates reported; whereas 2012 estimates reported that 1 in 88 children were likely to be diagnosed with ASD, the CDC's Morbidity and Mortality Weekly Report shows that 1 in 68 children were diagnosed with ASD in 2010.

Consistent with previous estimates, ASD remained five times more common among boys than girls, and white children were more likely to be diagnosed with ASD than black or Hispanic children.

Surveillance methods

The Autism and Developmental Disabilities Monitoring (ADDM) Network is an active surveillance system that provides estimates of the prevalence of ASD in children 8 years old from 11 ADDM sites in the United States. Overall ASD prevalence estimates varied among sites from 5.7 to 21.9 per 1,000 children aged 8 years.

Researchers noted that ADDM Network sites do not provide a representative sample of the entire United States, and the combined prevalence estimate presented in the report cannot be generalized to all US children aged 8 years.

Coleen Boyle.
Photo by the CDC.

In a CDC telebriefing, Coleen Boyle, PhD, MS Hyg, director of the National Center on Birth Defects and Developmental Disabilities, said the CDC autism tracking method provides the most complete picture of ASD in communities across the United States.

Findings were consistent with previous estimates that showed diagnostic patterns. “Most children with autism are not diagnosed until after age 4, even though autism can be diagnosed as early as 2,” Boyle said. “The earlier a child is identified, the better. The CDC encourages parents to take a proactive stance in tracking their child’s developmental milestones.” Per the results, the median age of earliest-known ASD diagnosis was 53 months and did not differ significantly by sex or race/ethnicity.

Intelligence, function rates

The survey also identified an emerging trend for the diagnosis of high-intelligence and high-functioning ASD. Study findings confirmed that 31% of children with ASD were classified as having IQ scores in the range of intellectual disability (IQ≤70), 23% in the borderline range (IQ=71-85) and 46% in the average or above-average range (IQ>85).

“Over the last decade, the most notable change in the characteristics of children identified with autism is the growing number who have average or above average intelligence, from one third in 2002 to nearly 50% in 2010,” Boyle said. She suggested that doctors are becoming more skilled at identifying autism symptoms, that there could be a growing number of children with autism and higher intellectual ability or that it may be a combination of the two factors.

“There is an urgent need to do more research, and an urgent need to put these findings to work for children and families. More is understood now about autism than ever before, but these numbers are an important reminder of the need for answers,” said Boyle.

For more information on new CDC ASD care initiatives, Boyle encouraged families and physicians to visit www.cdc.gov/milestones.