A large study has found that the rate of children with autism in a portion of a South Korean city was more than double previous national estimates in other countries, leading researchers to call for similar reviews in the United States and abroad to better gauge the disorder's true extent.
The study, published Monday, found that 2.6 percent of the region's children were diagnosed with autism spectrum disorder, more than double the 0.7 to 1 percent now regularly found in other countries, including the United States.
Candice Burns Hoffman, a spokeswoman for the federal Centers for Disease Control and Prevention, said the agency was considering a total population survey in light of the study. The CDC estimates the U.S. rate by using medical and special education records.
"It's a massive study. I commend them for their work," said Kate McFadden, a University of Pittsburgh autism researcher who did not work on this project.
Researchers emphasized the study didn't say more people have autism than before, just that it appears more people are diagnosed as methods improve and the disorder's spectrum is expanded to include milder forms, such as Asperger's syndrome.
The American Journal of Psychiatry published the study, done by researchers from the Yale Child Study Center in New Haven, Conn., George Washington University in Washington, D.C., and institutions in Korea.
Funded largely by a grant from the advocacy group Autism Speaks, researchers attempted to do a "total population" study. Every child between 7 and 12 years old in Goyang City's Ilsan district, population 488,590, was screened for autism -- not just the high-risk groups already identified by schools.
"In previous studies, they targeted narrow groups of children who were high risk," said Young-Shin Kim, the lead researcher and an epidemiologist at the Yale center. "But ... we wanted to know what percentage of autism was in the total population of children."
Researchers contacted parents of 36,592 students, of which 63 percent eventually participated, as well as 35 percent of the parents of 294 high-risk students already receiving some disability support in the district.
In the end, 2.6 percent of the district's 7- to 12-year-old students registered on the autistic spectrum from severe to mild.
"A total population study will always yield somewhat higher rates," said Roy Richard Grinker, the study's senior author and a GWU professor of anthropology and international affairs. "We just didn't know it would be this high."
The figure surprised outside researchers and even the study's sponsors.
"It was a very provocative clue that maybe we can do better to identify children in the spectrum so they can get the services they need," said Andy Shih, Autism Speaks' vice president of scientific affairs.
Two-thirds of those deemed autistic were in regular classroom settings, not receiving support services. The remaining third were already in the district's disability register, receiving some assistance.
Grinker said the study's rate of high-risk students who were found to be autistic -- about 0.7 percent -- was about the same percentage as what CDC has estimated for the U.S. population.
Kim said that because South Korea's educational system is highly structured and has such large classrooms -- of 35 to 40 students -- autistic children would draw attention only if they acted out. Most students who screened positive in the study's first stage were identified through questionnaires from their parents.
Autistic students had an average IQ of 98, as did the rest of the students, so they'd probably pass their classes, Kim said.
"However, when we look back to our own childhoods and classrooms, we can all recall that one or two kids were not fitting in with the rest of the kids," she said. "... Now we have a proper name for these children, and we have ways to help them."