Atlanta About one in 150 American children has autism, U.S. health officials said Thursday, calling the troubling disorder an urgent public health concern that is more common than they had thought.
The new numbers are based on the largest, most convincing study done so far in the United States, and trump previous estimates that placed the prevalence at 1 in 166.
The difference means roughly 50,000 more children and young adults may have autism and related disorders than was previously thought - a total nationwide of more than half a million people.
Advocates said the study provides a sad new understanding of autism's burden on society, and should fuel efforts to get the government to spend hundreds of millions of additional dollars for autism research and services.
"This data today show we're going to need more early intervention services and more therapists, and we're going to need federal and state legislators to stand up for these families," said Alison Singer, spokeswoman for Autism Speaks, the nation's largest organization advocating services for autistic children.
The study by the U.S. Centers for Disease Control and Prevention was based on 2002 data from 14 states. It calculated an average autism rate 6.6 per 1,000, compared with an estimate last year of 5.5 in 1,000.
"Autism is more common than we believed," said Catherine Rice, a CDC behavioral scientist who was the study's lead author.
The research was based on 2002 data from all or part of 14 states. It involved an intense review of medical and school records for children and gives the clearest picture yet of how common autism is in some parts of the country, CDC officials said.
The results suggest 560,000 children and young adults have the condition.
However, the study population is not demographically representative of the nation as a whole, so officials cautioned against using the results as a national average. The study doesn't include some of the most populous states like California, Texas and Florida.
Also, the study does not answer whether autism has recently been on the rise - a controversial topic, driven in part by the contention of some parents and advocates that it is linked to a vaccine preservative. The best scientific studies have not borne out that claim.
"We can't make conclusions about trends yet," because the study's database is too new, Rice said.
Autism is a complex disorder usually not diagnosed in children until after age 3. It is characterized by a range of behaviors, including difficulty in expressing needs and inability to socialize. The cause is not known.
Scientists have been revising how common they think the disorder is. Past lower estimates were based on smaller studies. The study released Thursday is one of the first scientific papers to come out of a more authoritative way of measuring it.
"This is a more accurate rate because of the methods they used," said Dr. Eric Hollander, an autism expert at New York's Mount Sinai School of Medicine.
The study involved 2002 data from parts or all of 14 states - Alabama, Arizona, Arkansas, Colorado, Georgia, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah, West Virginia and Wisconsin.
Researchers looked specifically at children who were 8 years old because most autistic kids are diagnosed by that age. The researchers checked health records in each area and school records when available, looking for children who met diagnostic criteria for autism. They used those numbers to calculate a prevalence rate for each study area.
Included were autism-linked conditions like Asperger disorder, which some experts say might partly account for the higher rate.
Dr. Fred Volkmar, director of the Child Study Center at Yale University, said the educational records researchers relied on in some states may be misleading. Sometimes, if a child has problems that seem like autism, parents will push for an autism label to get additional educational services, he said.
Rates varied dramatically among states, in some cases. The rate was 3.3 per 1,000 in the northeastern Alabama study area and 10.6 per 1,000 in the Newark, N.J., metro area.
Researchers say they don't know why the rate was so high in New Jersey. They think the Alabama rate was low partly because of limited access to special education records.
The study was not an effort to find the cause of autism, still a point of debate. While many advocacy groups blame the vaccine preservative thimerosal, scientists are putting more focus on possible genetic causes, according to a recent Stanford University study.