About 1 in 110 U.S. children suffers from autism spectrum disorders, a broad classification that includes autism, Asperger's syndrome and pervasive developmental disabilities, the Centers for Disease Control and Prevention reported today in its Morbidity and Mortality Weekly Report. The data, which were released on a provisional basis in October, coincide well with other estimates of autism prevalence, including a report in the journal Pediatrics that same month.
The new data represent a 50% increase from two years ago, when the agency estimated the prevalence of the disorder at about 1 in 150 children. At least some of the increase comes from better diagnosis of the disorder, but some apparently also comes from a complex mix of genetic and environmental factors -- although it is not clear what those factors might be. The new study did not investigate potential causes of the disorder, said lead author Catherine Rice, a behavioral health scientist at the CDC's National Center on Birth Defects and Developmental Disabilities. Other CDC groups are looking at potential causes, she said.
The study focused on children who were 8 years old in 2006, the most recent year for which data were available, because other studies have shown that most cases of autism spectrum disorders are diagnosed by that age. The researchers studied case records of children at 11 sites on the Autism and Developmental Disabilities Monitoring Network, which covers about 8% of U.S. children. Case records were reviewed to ensure that appropriate diagnostic criteria for the disorders were met, but the children were not studied directly.
The researchers found that 2,757 of 307,790 8-year-olds in the sites had an autism spectrum disorder, an overall prevalence of 9 per 1,000. Rates at individual sites ranged from a low of 4.2 per 1,000 in Florida to a high of 12.1 in Arizona and Missouri. Rice said it is likely the low rates represent an underreporting, but she had no explanation for the states with the highest rates.
Boys were about 4.5 times as likely as girls to be diagnosed with the disorder, which matches well with earlier studies that found about 80% of victims are male. That means that about 1 in 70 boys suffers from the disorder, compared with about 1 in 315 girls. The average age of diagnosis was 4.5, about five months earlier than had been the case in 2002.
-- Thomas H. Maugh II