ATLANTA -- About one in 150 American children has autism, an urgent public health concern, said U.S. health officials Thursday who reported on the largest study done so far on the troubling disorder.
The new numbers, based on 2002 data from 14 states, are higher than previously reported.
Advocates said the study provides a sad new understanding of how common autism is, and should fuel efforts to get the government to spend hundreds of millions of additional dollars for autism research and services.
"This data today shows 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 more services for autistic children.
The study by the U.S. Centers for Disease Control and Prevention calculated an average autism rate 6.6 per 1,000. That compares with last year's estimated rate of 5.5 in 1,000.
The research involved an intense review of medical and school records for children in all or part of 14 states and gives the clearest picture yet of how common autism is in some parts of the country, CDC officials said.
However, those states are 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 is increasing -- a controversial topic, driven in part by the contention by some parents and advocates that autism 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, said Catherine Rice, a CDC behavioral scientist who was the study's lead author.
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 estimates from smaller studies have ranged from 1 out of every 10,000 children to nearly 1 in 100.
Last year's estimate of 5.5 out of every 1,000 U.S. children was based on national surveys of tens of thousands of families with school-age children. That fit into a prevalence range found in other recent studies.
The CDC also has been developing an alternate way of measuring autism prevalence, building a network of university and state health departments for ongoing surveillance of autism and developmental disabilities. The study released Thursday is one of the first scientific papers to come out of that effort.
"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 that year. They said most children with autism are identified for medical or educational services by that age.
The researchers checked health records in each area and school records when they were made available, looking for children who met diagnostic criteria for autism. They used those numbers to calculate a prevalence rate for each study area.
The rates varied from 3.3 per 1,000 in the study site in Alabama, which was made up of the state's 32 northernmost counties, to 10.6 in the site in New Jersey, which involved four counties, including metropolitan Newark.
Researchers say they don't know why the rate was so high in New Jersey. They think the Alabama rate was low at least partly because researchers had limited access to special education records there.