Federal health authorities have significantly raised their estimate of the prevalence of autism in children, concluding in a new study of 8-year-olds that 1 in 88 has some form of the disorder.
The analysis, based on a review of tens of thousands of health and school records in 14 states, was released Thursday by the U.S. Centers for Disease Control and Prevention. It is the latest in a series of studies showing autism rates climbing dramatically over the last decade. The previous estimate was 1 in 110.
While the new numbers are sure to fuel debate over whether a growing environmental threat is at work, researchers said the data suggest that rising awareness of the disorder, better detection and improved access to services can explain much of the increase, and perhaps all of it.
Dr. Daniel Geschwind, an autism expert at the University of California at Los Angeles, said he was initially surprised by the size of the increase — 25 percent in just two years.
"But when I looked at what seems to be driving it, it made total sense," he said.
He and other experts said vast differences in the rates among states included in the study are almost certainly a reflection of social and cultural factors that influence who gets a diagnosis.
"Public awareness has gone up and case identification has gotten better," said Dr. Young-Shin Kim, an autism expert at Yale University.
Nobody knows what causes autism, and there is no blood test, brain scan or other biological marker. It is diagnosed by its symptoms — social and communication difficulties starting in early childhood as well as repetitive behaviors or abnormally intense interests.
Autism rates have exploded since the 1990s as the definition expanded to include milder cases, efforts to identify the disorder intensified and publicly funded services became more widely available.
In response to rising public concern, the CDC set up a network of surveillance sites across the country. Researchers did not examine any children but instead periodically scoured health and special education records of hundreds of thousands of 8-year-olds in search of the signs of autism or an actual diagnosis.
In its first analysis, using data from 2000, it estimated that 1 in 150 children had some form of the disorder. By 2006 it was 1 in 110.
The latest estimate of 1 in 88, based on 2008 data, is already being touted as evidence that autism is an epidemic and that something in the environment is driving it.
"Autism is now officially becoming an epidemic in the United States," said Mark Roithmayr, president of the advocacy group Autism Speaks, who used the occasion to call for more government funding for research and treatment.
In all, the CDC identified 3,820 children as having some form of autism, out of 337,093 children in its surveillance area.
Though the overall rate was 1 in 88, it varied considerably among the 14 sites, from 1 in 47 in Utah to 1 in 208 in Alabama. The rates also varied by race, with prevalence at 1 in 127 for Hispanics, 1 in 98 for blacks and 1 in 83 for whites.
Such differences have long been a feature of the CDC numbers. The latest numbers, however, show the geographic and racial gaps narrowing.
Prevalence studies that rely on records are inherently limited, said Kim, the Yale autism expert.
In a study published last year, her research team attempted to screen all 55,000 children in a suburb of Seoul, South Korea, and found that 1 in 38 met the current definition for some form of autism.
Two-thirds had never been identified with autism or any other disability and, though they often struggled socially, they were in regular classrooms.
Had the researchers used the CDC methodology, Young-Shin said, they would have missed all of those cases.
Young-Shin and many other researchers see the boom in diagnosis as a positive step, a chance to bring help to children who would have been missed in the past.
But the Korea study also served as evidence for some researchers that the definition left too much room for interpretation.