A new government survey finds that more than 2 percent of U.S. kids have been diagnosed with autism — or 1 in 45 children aged 3 and older.
That seems like a startling increase from the last estimate of 1 in 68 kids.
But the researchers are quick to point out that the latest survey was done in a new way, asking parents different questions about their kids and any diagnosis of autism. They say it's probably the most accurate estimate yet, and stress that it almost certainly doesn't show some big increase in autism actually occurring among children.
Instead, they say, it's clear that doctors are changing the way they diagnose autism, and that parents are far more likely than in years past to seek a diagnosis for their kids.
"One in 45 is what we think is the most accurate parental report of autism to date. I think within this report we found that the way that we ask the parents about autism spectrum disorder can have an impact on the way the parents respond to the question," said Benjamin Zablotsky, an epidemiologist at the National Center for Health Statistics who helped lead the study.
"We feel we are asking the question in a better way than before," he said.
It's a hot topic in the U.S., with many parents and advocacy groups saying something must be happening to make so many kids develop autism. Other experts say it's almost certainly more likely that the condition is being recognized and diagnosed more often.
Zablotsky's team got their data from detailed surveys of 35,000 U.S. households. Parents of children aged 3 to 17 were asked specifically if their child had ever received a diagnosis of autism.
"The estimated prevalence of ASD (autism spectrum disorder) based on 2014 data was 2.24 percent, a significant increase from the estimated annualized prevalence of 1.25 percent based on 2011-2013 data," they wrote in their report released Friday.
"In contrast, the prevalence of other developmental disorders declined significantly from 4.84 percent based on 2011-2013 data to 3.57 percent based on 2014 data," they wrote.
"It's a high number and it's a scary number," said Michael Rosanoff, director of public health for the advocacy group Autism Speaks. "It's another piece of evidence suggesting we are under-reporting the prevalence of autism in the U.S."
Earlier questionnaires were a bit more complicated, with parents being asked if a child had ever been diagnosed with a developmental disorder, including autism. This may have been confusing, Zablotsky said.
"In previous years, it is likely that some parents of children diagnosed with autism spectrum disorder reported this developmental disability as other developmental disorders instead of, or in addition to, ASD," his team wrote.
Dr. Lisa Shulman, an autism specialist in the pediatrics department of the Albert Einstein College of Medicine, said it's often hard to clearly define autism to parents, and difficult for people to remember what diagnosis a child got.
"That is definitely the take-home message. It's hard to get a number," Shulman told NBC News.
Autism spectrum disorder refers to a large range of conditions, from the relatively mild symptoms of Asperger's to severe and profound intellectual deficits and an inability to communicate with others. Symptoms often overlap with other disorders such as attention deficit/hyperactivity disorder, cerebral palsy or various learning disorders.
The Centers for Disease Control and Prevention has been studying how common autism is for years now, since parents began worrying that perhaps something kids were exposed to — notably vaccines — might cause autism. Many studies have shown vaccines do not cause autism, and CDC has promised to try to find out what is causing it.
Every year, the number of cases diagnosed goes up. In the latest study before this one, CDC found a 30 percent spike in autism diagnoses among 8-year-olds between 2008 and 2010 to 1 in 68 children.
There are certainly genetic links, and some evidence that infections in pregnancy, such as influenza, might play a role, as well.
Laurie Alderman, a research scientist in George Washington University's Department of Special Education and former coordinator of autism services for Arlington County Public Schools in Virginia, says she doesn't think there's much more autism now than there was 30 or 40 years ago.
"These kids have always been there," Alderman told NBC News. "I started teaching in 1979 and I have always had students who were a little quirky, a little odd, a little rigid."
Some kids were just kept in classrooms with everyone else. Others were classified as disabled. "These kids were in special education because they had 'mental retardation' or a physical disability, a learning disability, ADHD," she said.
Now autism is something commonly talked about, and there's growing evidence that kids can be helped.
"There are so many more professionals who can diagnose autism now," Alderman added. "It used to be when I started out and parents were asking about this you had to go to major medical center to get an autism diagnosis."
Children are also diagnosed at much younger ages than before, she noted.
And parents now know they can get services for their children with an autism diagnosis, all the experts agree.
"Money follows diagnosis. And there's a lot more money that's attached to a diagnosis of autism than there would be to a diagnosis of developmental language disorder or ... a learning disability to give you an example," said Dr. Max Wiznitzer, a child neurologist at Rainbow Babies & Children's Hospital in Cleveland. "And with more money, you can provide more services."
Wiznitzer agrees that kids now diagnosed with autism would have had "another label" in the past.
"We're just changing a child's diagnosis from, let's say, intellectual disability and mental retardation to autism spectrum disorder," he said.
"Certainly one reason for the increase over time is that parents do come seeking the diagnosis," Shulman added.
The findings fit in with other studies seeking to show whether autism is actually occurring more frequently, or simply being recognized and diagnosed more often. A team at Penn State University also found that children are being reclassified from something broad, like pervasive developmental disorder, to the more specific autism.
And the NCHS found earlier this year that as many as 9 percent of children diagnosed with autism don't actually have it.