The prevalence of parent-reported cases of autism is significantly higher now than it was just five years ago, according to new Centers for Disease Control and Prevention data released Wednesday.
From 2011 to 2012, 1 in 50 school-age children had a diagnosed autism spectrum disorder according to their parents -- up from 1 in 86 in 2007.
"[This] study provides growing evidence that [the] U.S. is underestimating the prevalence of autism spectrum disorder," Michael Rosanoff, associate director of public health research and scientific review at the non-profit Autism Speaks, said in an e-mail to HuffPost. Rosanoff did not work on the new report, but he had reviewed it.
The new figures came from the 2011 to 2012 National Survey of Children's Health, a national telephone survey conducted by the CDC. In this most recent survey, parents reported that 2 percent of 6- to 17-year-olds had a diagnosis for an autism spectrum disorder, which is higher than the 2007 estimate of 1.16 percent.
Overall, the increase was greater for boys than for girls, and among 14- to 17-year-olds than younger children.
The report's authors largely attribute the change to doctors identifying the disorder more often now than they did just a few years earlier. "Much of the prevalence increase from 2007 to 2011 [to] 2012 for school-aged children was the result of diagnoses of children with previously unrecognized ASD," they wrote.
"The way I read this [report] is that a large part of the increase is attributable to that," said Tristam Smith, a professor of neurodevelopmental and behavioral pediatrics at the University of Rochester Medical Center, referring to increased detection. "But is it the only thing? It's hard to say."
Last year, the CDC revised its go-to estimate of the prevalence of autism in the U.S., saying it now affects 1 in 88 children, up from 1 in 150 in 2002. That is the estimate most widely used by health care providers, public health officials and media outlets when quantifying the prevalence of autism in the U.S., and came from the CDC's Autism and Developmental Disabilities Monitoring Network, which collected data from health and special education records of 8-year-olds living in 14 communities across the country in 2008.
Because the two estimates used different approaches to identify cases, they are not directly comparable, but Rosanoff believes the new parental-report data suggests that "1 in 88" figure is low.
Autism spectrum disorders are a group of developmental disorders characterized by social, communication and behavioral challenges. There is no biological test for autism, nor do researchers know its cause, although a rapidly growing body of scientific research suggests it is a combination of genetic and outside or "environmental" factors.
Getting a clearer picture of autism's true prevalence will help researchers set a benchmark that allows them to better understand if the disorder is simply being identified more by doctors; if actual risk has increased -- or both, Smith said.
"We need to double-down on our efforts to get a full picture of what's going on," he argued. "I think it's very critical for understanding where to look for the etiology or etiologies of autism. It's also critical in service delivery." A lengthy December 2012 report by a federal advisory committee that oversees autism research found that there are significant gaps in how much services are studied as well as their availability.
"It's an important study," Smith concluded. "It definitely adds to the picture, but it also adds to the mystery of what's going on."