The largest U.S. study of childhood autism to date has found that about 1 in 150 have the disorder — a higher prevalence than previous national estimates.
The autism rate was about 6.6 per 1,000 in the new study based on data from 2002. It was released Thursday by the U.S. Centers for Disease Control and Prevention. Last year, the agency had estimated the rate was about 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.
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.
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 kids. That fit into a prevalence range found in other recent studies.
More accurate count
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.
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.
