Rates of all forms of autism in the U.S. may be substantially higher than previously estimated, according to a new government report that found that 1 out of every 50 school-age children - roughly one on every school bus - has the condition.
That's dramatically higher than the 1 in 88 announced by a different government agency last year. The numbers keep climbing in part because of different methods of counting.
The present study asked 100,000 parents across the country a range of health questions, including whether their child had been diagnosed on the autism spectrum and whether he or she currently had the diagnosis. The autism spectrum includes autism, the most severe form, as well as Asperger's syndrome and pervasive developmental disorder-not otherwise specified (PDD-NOS).
The study looked at children ages 6-17 and was based on parent reports, while last year's study looked at 8-year-olds whose diagnosis was noted in school district or other official records.
The fact that the new study found such high rates implies that "there will likely be more demand for (autism-related) services than we had previously thought," said study author Stephen J. Blumberg, a senior scientist at the National Center for Health Statistics.
The new study, like most others, found that boys are four times more likely to have autism than girls.
The parents' answers to the two survey questions also suggests that 15% to 20% of children who were once diagnosed with autism no longer have the condition. Blumberg said the study cannot say whether they lost the diagnosis because they outgrew the condition, or because they were misdiagnosed in the first place.
The higher numbers recorded in the new study suggest that officials are getting better at counting kids with autism - not that more have the condition, several experts said.
"I don't see any evidence that there's a true increase in the prevalence of autism," said Roy Richard Grinker, a professor of anthropology at George Washington University, Washington, D.C.
Grinker said he's been anticipating a higher count in the United States since he published a 2011 study that found an autism rate of 1 in 38 in South Korean children. "I don't look at that and say 'that's so much higher than the U.S.' I look at that as 'the U.S. will catch up.'"
The new study found the biggest jump among older children with milder symptoms, suggesting that their autism wasn't caught until later in childhood. By definition, symptoms of autism must be present by age 3, affect a child's communication and social skills, and lead to restricted or repetitive behaviors such as rocking or hand-flapping.
Michael Rosanoff, associate director of research for the advocacy group Autism Speaks, said he thinks the new numbers reflect improved awareness of the condition over the past decade, leading to more diagnoses. Because these children weren't counted in earlier studies looking at school district support, it also suggests that many children who need help with their symptoms aren't getting it, Rosanoff said.
It is the children with milder symptoms who are most likely to be affected by a change in the definition of autism that will take place this spring. Rosanoff said this study adds urgency to the need to protect those children.
"We need to make sure that with the change in diagnostic criteria we're certain that individuals who require services will still have access to them," he said.