U.S. Autism Estimates Rise by 30 Percent for Kids
Researchers say increase could be due to better diagnosis of the developmental disorder
Autism experts believe the increase reported by the CDC is more likely due to improved detection of the disorder, particularly among children at the higher-functioning end of the autism spectrum.
For example, almost half of children identified with autism spectrum disorder in the new study have average or above average intellectual ability, compared to one-third of children a decade ago.
"We are looking much more carefully, and we are getting better at finding kids at both ends of the spectrum, in particular the higher end of the spectrum," Nishawala said.
At the same time, the experts believe there are likely even more kids with autism than reported, given possible flaws in the CDC's surveillance system.
"We feel the way the CDC measures autism misses cases and is under-representing it," Rosanoff said. "This new number doesn't surprise us, but we feel it still may not be an accurate reflection of the true public health challenge."
The CDC network tallies cases that come to the attention of physicians or educators, which then are verified through a comprehensive evaluation and a review of school and medical records. But if the case doesn't attract attention, or if records aren't available to substantiate the diagnosis of autism, then the network will overlook that case, Rosanoff said.
For example, autism rates vary widely from state to state, ranging from one in 175 children in Alabama to one in 45 children in New Jersey -- an indication that some states are doing a better job of detecting and tracking autism. So, the total estimate could be skewed, Rosanoff said.
"All of the variation in prevalence between sites is due to the quality of records between sites," he said. "Those sites with better records have higher prevalence. In places where detection isn't as good, you're going to have a lower number."
These discrepancies also could explain why white children are much more likely to be diagnosed with autism, Nishawala said.
The new CDC report found that white children were approximately 30 percent more likely to be identified with autism than black children and almost 50 percent more likely than Hispanic children.
The CDC report was published in the March 28 issue of the agency's Morbidity and Mortality Weekly Report.
On Wednesday, researchers reporting in the New England Journal of Medicine said children with autism show key "patches of disorganization" in the outer layers of the brain. The researchers said this offers more evidence that the developmental disorder begins in the womb.
Researchers have managed to find a few hundred genes that are linked to autism risk. And although there is no definite environmental culprit, studies have tied certain factors during pregnancy to an increased risk, including exposure to high levels of air pollution, low intake of the B vitamin folate and viral infections.