One in 88 children is diagnosed with an autism spectrum disorder, or ASD, by age 8, according to a study released today by the U.S. Centers for Disease Control and Prevention -- a rate that has risen far above the 2006 estimate of 1 in 110.
But experts remain locked in debate about whether these numbers tell the whole story.
The CDC report, which analyzed data from 2008, indicates a 23 percent rise in diagnoses of ASDs over a two-year period.
The news could be most alarming for boys. The study reports that on average 1 in 54 boys was diagnosed with autism, compared to only 1 in 252 girls.
But what this rise actually means is still a mystery. Some doctors contacted by ABC News believe a broader definition of autism has contributed to rising rates.
"I think it has to do with changing diagnostic criteria, including mine over the years which have made me label many more children as being on the autism spectrum than say 10-20 years ago," said Dr. Isabelle Rapin, professor of pediatrics and neurology at the Albert Einstein College of Medicine. "Not only physicians, but parents, teachers, therapists and the public are much more aware of the symptoms of autism, and I suspect some may apply the diagnosis based on one symptom, which is inadequate."
Dr. Lisa Shulman, also at the Albert Einstein College of Medicine, echoed this concern.
"Over the years, children with autistic disorder remain a relatively small group in our center," said Shulman, director of Infant and Toddler Services at Einstein and an associate professor of pediatrics. "It is the group of children with milder social-communicative impairment and without a large array of mannerisms and atypical interests consistent with an ASD diagnosis that has increased significantly."
The data was collected by The Autism and Developmental Disabilities Monitoring network, an organization funded by the CDC to track autism rates. For this report, the ADDM reviewed medical records of 8-year-old children from 14 different areas across the country.
The study focused specifically on 8-year-olds because most autism spectrum diagnoses are made by the time a child reaches their eighth birthday. The signs of autism are often seen much earlier, however. Some experts believe that the first hints of abnormal behavior can be seen as early as 6 to 12 months.
"If parents suspect something is wrong with their child's development, or that their child is losing skills, they should talk to their pediatrician or another developmental expert," said Rebecca Landa, director of the Center for Autism and Related Disorders at the Kennedy Krieger Institute in Baltimore, Md., in a news release. Landa has published a list of 10 infant behaviors to watch for that may herald a developmental problem.
Still, experts say that parents need not start analyzing their babies just yet.
According to the CDC, a child should only be diagnosed with an Autism Spectrum Disorder (ASD) if they meet criteria for one of three diseases outlined in The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, commonly referred to as the DSM-IV.
These are Autistic disorder, Pervasive developmental disorder -- not otherwise specified, or Asperger disorder. Generally, the CDC describes them as, "a group of developmental disabilities characterized by impairments in social interaction and communication and by restricted, repetitive, and stereotyped patterns of behavior." The CDC has also published extended definitions for these disorders online.
A proposed change for the upcoming fifth edition of the DSM would include Asperger disorder as a sub-category of Autistic disorder. It is not known how this change might affect autism reporting in the future, but research is under way to answer this question.
Autism Cases Rise; Overdiagnosis, or Something Else?
But as for the new research, the CDC was quick to caution that these results may not be applicable to the whole country, as data from only certain sites around the nation was collected. This means that the CDC report relies on the records of many different providers across the country.
Numbers aside, scientists are still searching for what causes autism in the first place.
David Amaral, director of research at the UC Davis M.I.N.D. Institute and past president of the International Society for Autism Research, suggests that this new CDC report "will continue to fuel concerns that environmental factors, which are perhaps largely unidentified, may be increasing the prevalence of autism."
In particular, when asked about vaccines -- which have been a lightning rod for some advocacy groups in past years -- experts are quick to point out that studies have shown no connection to autism.
"As we know from political campaigns, stating a claim repeatedly can lead to a public belief in the concept since these conclusions are not always based on rational thought processes but also on emotional thinking and preconceived notions," says Dr. Max Wiznitzer, associate professor of pediatric neurology at Rainbow Babies and Children's Hospital in Cleveland, Ohio.
"It is clear that more parents are asking questions about vaccines and autism ... with most being reassured when given accurate information and being allowed to be part of the decision making process."
And some doctors said the increase in mild cases being identified may have a silver lining for parents.
"A diagnosis of autism spectrum disorder is no longer the 'kiss of death' it used to be," Rapin said, adding that in some situations, "parents are often eager for the diagnosis because services may be better than for other disorders."