ATLANTA -- As many as one in 50 U.S. school age children have a diagnosis of autism, up 72 percent since 2007, but much of the increase involves milder cases, suggesting the rise is linked to better recognition of autism symptoms and not more cases, government researchers said on Wednesday.
Overall, the telephone survey of more than 100,000 parents found about 2 percent of children ages 6 to 17 have autism, up from 1.16 percent in 2007, the last time the study was conducted.
"That translates to 1 million school age children ages 6 to 17 who were reported by their parents to have autism spectrum disorder," said Stephen Blumberg, a senior scientist at the National Center for Health Statistics, a part of the U.S. Centers for Disease Control and Prevention, who led the study.
As with prior estimates, boys were much more likely to be diagnosed with autism than girls, with 1 in 31 school-age boys, or 3.2 percent, having an autism diagnosis, compared with 1 in 143, or 0.7 percent of girls, having a diagnosis.
"Boys were more than 4 times as likely as girls to have autism spectrum disorder," Blumberg said.
He said the increase among boys accounted for nearly all of the overall increase in autism diagnoses.
The new findings differ sharply from autism data released just a year ago by the CDC, which said 1 in 88 children in the United States had autism, a spectrum of disabilities that can range from highly functioning individuals to those with severe speech and intellectual disabilities.
In general, individuals with autism struggle with difficulties in communication, behavior and social interaction.
In the current study, the researchers surveyed parents of children age 6 to 17 as part of the 2011-2012 National Survey of Children's Health or NSCH. They compared their findings to the same study done in 2007, which found 1 in 86 children had an autism diagnosis.
The estimate from last year involved a review of medical and educational records of 8 year olds in 14 sites around the country. Data in the records were last collected in 2008, so the finding of 1 in 88 is not far off from the 1 in 86 figure in 2007, the starting point of the current study.
Blumberg said much of the increase in the estimates from the current parent survey was the result of diagnoses of children with previously unrecognized autism.
Increased awareness of autism differences in children and better detection of autism symptoms by doctors, especially in children with milder cases, likely accounts for the increased diagnoses.
"We think the improved recognition is really a recognition of autism spectrum disorders in children with previously unrecognized autism as opposed to new cases," Blumberg said
Symptoms of autism can be seen in children as young as 18 months of age, and doctors are urged to conduct a screening for developmental delays on all children by age 2. But doctors often fail to detect mild cases of autism until children enter school, when parents become aware of their child's troubles making friends and teachers notice differences in the child's ability to interact socially, the team said.
"This is not saying anything about an increased risk for autism but rather that the NSCH is capturing more of the cases that had been missed previously," said Michael Rosanoff of the advocacy group Autism Speaks.
For families, the findings mean detection of autism, particularly milder forms, is improving but could still happen earlier.
"Even mildly affected children who are in general education settings can struggle without and benefit from appropriate autism spectrum disorder services," he said in an e-mail.
While scientists believe genetics account for 80 to 90 percent of the risk for developing autism, a growing number of studies are beginning to suggest that a father's age at the time of conception may play a role by increasing risks for genetic mistakes in the sperm that could be passed along to offspring.
And new research by a British team found that older fathers are more likely to have grandchildren with autism, suggesting that risk factors for autism may build up over generations.