Beth Bullen, a 44-year-old registered nurse in Caledonia, N.Y., is no stranger to autism spectrum disorders, or ASD. Her 10-year-old son has a severe form of autism, while her 13-year-old son has Asperger's syndrome.
"How they wrote, how they organized, their handwriting, their delay in crawling and walking -- that's when bells and whistles started going off," she said. "My oldest son didn't walk until he was 2, and didn't crawl until he was 15 months old. My younger son was majorly speech delayed."
So when the U.S. Centers for Disease Control and Prevention released a report on Friday stating that almost 1 percent of American children had ASD, she said she was not shocked by the numbers.
"I don't think any of us parents are surprised, because I don't think what's common knowledge is that there are quite a few families that have children on the autism spectrum," Bullen said. "I have talked to families who have children with 3 or 4 children on the spectrum. I think we all know someone who is on the autism spectrum."
But while some parents might not have been shocked, those in the medical community say the numbers give pause.
"These numbers always sort of take our breath away," said Dr. Janet Farmer, professor and director of academic programs at the Thompson Center for Autism and Neurodevelopmental Disorders at the University of Missouri. "I think those of us in the scientific community are quite shocked by this."
The report, based on data collected by the CDC's Autism and Developmental Disabilities Monitoring Network in 2006, tracked prevalence of autism spectrum disorders in children 8 years of age from 11 areas of the U.S., including parts of Alabama, Arizona, Colorado, Florida, Georgia, Maryland, Missouri, North Carolina, Pennsylvania, South Carolina, and Wisconsin.
Health and education records were reviewed to identify children with ASD, including autistic disorder, pervasive developmental disorder not otherwise specified, and Asperger disorder.
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What the report found was that across 11 sites in the United States, ASD prevalence in 2006 ranged from about one out of 80 children to one out of every 240 children, with an overall prevalence of one in 111 youngsters.
The findings appear in the Dec. 18th Morbidity and Mortality Weekly Report.
The overall estimate is slightly lower than that from a study using data from the 2007 National Survey of Children's Health -- one in every 91 children -- published just last October.
However, among 10 sites that reported data in both 2002 and 2006, there was an average 57 percent increase in ASD prevalence. No single factor could explain the rise, researchers said.
The new report also found that overall ASD prevalence was 4.5 times higher in boys than in girls: about one in every 70 boys and one in every 315 girls. From 2002 to 2006, prevalence increased 60 percent in boys and 48 percent in girls.
The researchers acknowledged that some of the increase could be attributed to better detection – but they added that the numbers also suggest that the overall increase cannot be attributed to detection alone.
ABC News Senior Health and Medical Editor Dr. Rich Besser said on "Good Morning America" Friday that, unfortunately, doctors and researchers are not much further along in their understanding of the underlying causes of this apparent surge.