It's a large increase since the last report but experts stress it doesn't necessarily mean more children are developing autism.
Instead, the numbers suggests that more children are being diagnosed as they get older – probably because of many factors, including increased awareness and more services both to diagnose children and help them, the researchers said.
"Our findings suggest that the increase in prevalence may be due to increased recognition of autism spectrum disorders in recent years, especially when the symptoms were mild," Stephen Blumberg of the National Center for Health Statistics, which published the report, said in a telephone interview.
"Parents are more aware. Professionals are more aware. There may be more access to diagnostic services."
Autism describes a range of conditions and disorders – some of which a few years ago were not even recognized as conditions. It can range from the very mild social awkwardness seen in some cases of Asperger's syndrome, to severe and debilitating symptoms that prevent children from interacting in a normal way, prevent learning and often require medication. Some children with autism were classified as mentally retarded in years past, while others struggled quietly with no idea they could benefit from therapy.
Parents should not worry that something new has been happening to kids, says Dr. Marshalyn Yeargin-Allsopp of the Centers for Disease Control and Prevention, which is monitoring autism in several ways. "We don't want them to be frightened by the numbers. We want them to recognize that there are things they can do that make a difference in their child's life," she said.
Image: School girl, via Shutterstock