Since the 1990s, there's been a dramatic increase in autism (search) among school-age children.

The data are from the U.S. Department of Education, and the report hints that the increases seen with time are real.

Research has suggested that the rise in autism could be largely explained by changes in diagnosis, with children who might have been classified as mentally retarded or speech impaired before the 1990s now being classified as autistic.

Lead researcher Craig J. Newschaffer, PhD, says the Department of Education figures do not show this, but he adds that the increase in autism may never be fully understood.

“I don’t know if we are ever going to be in a position to explain what has gone on over the last decade,” he says. “The hope is that with the surveillance programs that are now in place we will be in a better position to understand future trends.”

Earlier findings from the CDC and others have suggested as much as a tenfold increase in autism and related disorders during the last decade of the 20th century.

The study does not answer the question as to why autism is increasing. But the national data don't show a decrease in other learning disabilities. Trends for mental retardation (search) and speech and language impairment remained unchanged.

This suggests the increase in autism is not the result of an across-the-board increase in special education classification, say the researchers.

Trend May Be Leveling Off

Newschaffer and colleagues from an autism tracking center at the Johns Hopkins Bloomberg School of Public Health analyzed national special education data collected from 1992 to 2001.

The findings are reported in the March issue of the journal Pediatrics.

The research offers intriguing early evidence that the upward trend in autism cases may be beginning to level off. But Newschaffer cautions that the finding may be misleading.

He says a change in 1997 that allowed children up to the age of 9 to be classified as “developmentally delayed” may explain the apparent leveling of autism cases. Before 1997 the diagnosis was used only for children 5 and under.

It is possible, Newschaffer explains, that children with this label who would have been reclassified as autistic after age 5 are now being diagnosed when they are older.

“We will need a few more years of data to determine if the rise in autism is really leveling off,” he says.

Early Diagnosis Is Key

The most recent figures indicate that as many as one in 166 children in the U.S. is autistic or has an autism-related disorder, such as Asperger syndrome.

Despite a growing awareness of the importance of early diagnosis, the new report suggests that many children are still being diagnosed at older ages.

Last month, the CDC launched a major public health initiative to promote early diagnosis by raising awareness about child development milestones.

“By recognizing the signs of developmental disabilities early, parents can seek effective treatments which can dramatically improve their child’s future,” CDC Director Julie Gerberding, MD, says in a news release.

The focus of the campaign is to get parents to keep track of important developmental milestones such as when their child learns to smile, when they recognize the word "no," when they learn to speak and play, and how they interact with others.

Pediatrician and epidemiologist Marshalyn Yeargin-Allsopp, MD, says the hope is that parents will learn to identify developmental delays as early as possible. Yeargin-Allsopp is conducting an ongoing study of autism prevalence trends for the CDC.

“Parents need to know the signs and bring those signs to the attention of their health care provider,” she says. “After all, parents know their children better than anyone. And providers can’t take a 'wait-and-see' attitude. They have to refer a child quickly for diagnostic assessment even if they just suspect a developmental delay so that a child can get intervention services as early as possible, if necessary.”

By Salynn Boyles, reviewed by Brunilda Nazario, MD

SOURCES: Newschaffer, C. Pediatrics, March 3, 2005; vol 115: pp 277-282. Craig J. Newschaffer, PhD, Center for Autism and Developmental Disabilities Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore. Marshalyn Yeargin-Allsopp, MD, National Center of Birth Defects and Developmental Disabilities, CDC, Atlanta. News release, CDC.