Oct. 5, 2009 -- About 1% of U.S. children, or about one in 91, may have autism or an autism spectrum disorder, according to two new national surveys.
The new estimate is a dramatic increase from the previously accepted number of one in 150. But experts who discussed the findings of the two new surveys -- one released today and the other due out before year's end -- urged caution in interpreting the new information about the developmental disorders.
A new survey by the CDC found that about 1% of U.S. children are affected by an autism spectrum disorder, says Ileana Arias, PhD, deputy director of the CDC.
No further details were available on the CDC survey, due to be released in full later this year.
The same prevalence, however, was found in the survey released today, says Michael D. Kogan, PhD, of the Maternal and Child Health Bureau of the Health Resources and Services Administration. With his colleagues, Kogan drew on data from the 2007 National Survey of Children's Health, a telephone survey of parents jointly conducted by the Health Resources and Services Administration and the CDC.
The parents of more than 78,000 children ages 3 to 17 were asked if their child had ever been diagnosed with autism or other disorders on the spectrum, such as Asperger's syndrome or pervasive developmental disorder. If parents answered yes, they were then asked if their child currently had an autism spectrum disorder (ASD) and if so, how severe the condition was -- mild, moderate, or severe.
In all, 1,412 said their children had ever been diagnosed with an ASD, and 913 said their child still had the condition. Next, Kogan's team took the number of children in the survey with ASD and the total number of children surveyed and computed estimates of autism spectrum disorder prevalence based on the general population.
''We estimate that the prevalence of ASD among children 3-17 in 2007 was around 110 in 10,000,'' Kogan says. "What this translates to is about one in every 100."
The survey also showed that white non-Hispanic children were more likely than black non-Hispanic or multiracial children to have the diagnosis, he says. Boys were four times as likely as girls to have ASD.
About 38% of the parents said they had been told previously their child had an ASD but that the child did not currently have the condition. The survey results are published in the journal Pediatrics.
Interpreting the New Autism Data
Experts are not certain what to make of the findings but urged caution in interpreting them. "In ASD, we don't know if the change in the numbers over time is a change in the actual condition," Arias says, or to other factors.
Among the other factors are that awareness of the condition is more widespread, she says, and the condition is now thought about on a continuum, so what is now considered a mild case may not have been diagnosed in past years.
"We also know from other studies that there has been a decreasing average age of diagnosis, which would lead to increasing prevalence at any one point in time," Kogan says.
In recent years, experts have also realized that ASD often coexists with other disorders, such as attention deficit hyperactivity disorder, and a child who previously was only diagnosed with ADHD may now have a diagnosis of both ADHD and ASD, for instance.
And what of the 38% of children who seemed to have shed their diagnosis? "We know that some children diagnosed at young ages won't meet the criteria as they age," Kogan says. Some parents surveyed may have been reporting a health care provider telling them they suspected ASD, rather than the actual diagnosis, he says.
In addition, some research has suggested that some children do have resolution from the condition and lose the diagnosis with age.
Second Opinion
Experts who reviewed the survey for WebMD say it is a carefully done report. They, too, are uncertain about what to make of the dramatic rise. "What it may be is that the numbers are the same but we are capturing a milder form [in the survey]," says Susan Hyman, MD, associate professor of pediatrics and division chief of neurodevelopmental and behavioral pediatrics at the University of Rochester and chairwoman of the American Academy of Pediatrics' autism subcommittee.
''The big take-home message is that autism spectrum disorders are more common than we thought 50 or 60 years ago," says Susan Levy, MD, a member of the autism subcommittee of the American Academy of Pediatrics and an autism expert at Children's Hospital of Philadelphia. The newer surveys, such as the one published in Pediatrics, suggest the disorders are more common, she says, than people thought even 10 years ago. Like all surveys, however, Levy says, it may not be completely accurate.
For parents, the message is clear, whether the increase in numbers turns out to be totally representative of the population or not, experts say. It's important to know potential signs of ASD and to consult a pediatrician as soon as possible to check out the child, experts stress. Among the potential signs are social interaction problems, language difficulties, or behavior problems such as repetitive behavior.