"This is a large number of children and families affected by autism," study leader Marshalyn Yeargin-Allsopp, MD, chief of the CDC's developmental disabilities branch, tells WebMD.
"With nearly a doubling of prevalence since CDC started tracking in 1992, autism is officially becoming an epidemic in the U.S. We are dealing with a national emergency that is in need of a national plan," Mark Roithmayr, president of the advocacy group Autism Speaks, said at a CDC teleconference held to announce the findings.
More autism research and better services for people living with autism will be expensive. But the cost of autism already is astronomical, according to preliminary findings from an Autism Speaks-funded study by Martin Knapp, PhD, of the London School of Economics, and David Mandell, ScD, of the University of Pennsylvania.
At the new 2008 prevalence rate of one in 88 American children, autism costs the U.S. $137 billion a year. It has been estimated that 45% of Americans with autism have an intellectual disability. The lifetime cost for each person who has an intellectual disability related to autism is $2.3 million, Knapp and Mandell estimate.
Why the huge increase in autism? That isn't clear. A number of factors likely contribute to the increase, says Coleen A. Boyle, PhD, director of the CDC National Center on Birth Defects and Developmental Disabilities.
"We know that some of it is due to how children with autism are identified and served in their local communities," Boyle tells WebMD. "We do feel doctors are getting better at diagnosing autism. … But we don't know how much is due to better identification and diagnosis, how much is due to availability of services, and how much is a true rise in prevalence."
Roithmayr says there's a critical need to answer this question.
"The increase in prevalence is only partly explained by the broadening of the diagnosis, improved detection and more awareness," he said. "A large proportion of autism, some 50%, remains unexplained."
One hint comes from data showing that autism prevalence is higher in areas where doctors are better at diagnosing autism in kids with relatively high intellectual ability.
The CDC's huge multi-year Study to Explore Early Development (SEED), begun in 2008, is exploring various autism risk factors. The very first results should start coming out later this year. But since SEED follows kids from the time of their mother's pregnancy, it will take time for the study to mature.
It's known that autism results from a complex interaction between genetic and environmental influences. But it's not known which types of autism are most closely linked to which factors.