Approximately 1% of 8-year-old children in the United States meet criteria for an autism spectrum disorder, based on results of a nationwide study of 8-year-olds conducted in 2006.
“No single factor explains the change in prevalence,” said Catherine Rice, Ph.D., of the National Center on Birth Defects and Developmental Disabilities. Dr. Rice presented the study results in a telebriefing.
The study included health and education records from 11 communities throughout the United States participating in the Autism and Developmental Disabilities Network (ADDM). The project was funded by the Centers for Disease Control and Prevention. Dr. Rice and her colleagues at the CDC focused on 8-year-olds because most children with autism spectrum disorder (ASD) have been identified by this age. A team of clinicians reviewed the records to confirm ASD diagnoses and identified 2,757 children who met criteria for ASD (MMWR 2009;58[SS-10]:1–24).
The prevalence of ASD among 8-year-olds increased by an average of 57% between 2002 and 2006, based on data from 10 reporting communities that participated in the study in both years. This increase might be attributable to improved diagnostic techniques, but “a true increase in the risk for children to develop ASD symptoms cannot be ruled out,” the researchers said.
Increases in ASD occurred across sex, ethnicity, and cognitive function, but the most consistent pattern was the increase in ASD among boys, Dr. Rice said. Overall, the prevalence of ASD was 1 in 70 boys and 1 in 315 girls, which amounts to a four to five times higher prevalence in boys, compared with girls.
Dr. Rice advised all primary care physicians who suspect ASD in a child to refer the child for further diagnostic evaluation or intervention.
The researchers did not conduct in-person evaluations of each child, and the results were limited by variations in record keeping. The study was not designed to evaluate causes of ASD, but the findings suggest that more research is needed to determine how genetic and environmental factors interact to cause ASD spectrum symptoms, the researchers wrote.