ATLANTA (ASRN.ORG)- About 1 in 110 children have autism, according to the government's latest estimate released by the Centers for Disease Control and Prevention.

It's a small change from a 1 in 100 preliminary estimate that CDC officials made in October from the same study. CDC officials said the latest number comes from a more complete analysis of reports from 11 states.

Until recently, the CDC had been saying autism occurred in 1 in 150 children. The new CDC estimate looks at 8-year-old children who had been diagnosed with an autism spectrum disorder in 2006.

The increase may be due in part to better diagnosis and changes in how well records were kept in the study sites, said Catherine Rice, a CDC behavioral scientist who worked on the new report.

"At this point it's impossible to say how much is a true increase and how much is identification," she said.

Doctors do not know what causes autism, but have been investigating possible genetic and environmental triggers. Results from the environmental research are still years away, Rice said.

Officials from the National Institute of Mental Health published results of a 2007 telephone survey of parents that concluded that 1 in 91 children had autism. At the same time, the CDC released to the media its preliminary results of 1 in 100 from its own research.

The study is based on medical and school records of nearly 2,800 children in communities in Alabama, Arizona, Colorado, Florida, Georgia, Maryland, Missouri, North Carolina, Pennsylvania, South Carolina and Wisconsin.

Autism is diagnosed by making judgments about a child's behavior; there are no blood or biologic tests. For decades, the diagnosis was given only to kids with severe language and social impairments and unusual, repetitious behaviors. The definition of autism has gradually expanded, and "autism" is now shorthand for a group of milder, related conditions.

Health officials have urged stepped-up screening of children for autism, saying early therapy can improve how well children develop. While researchers have found that parents often voiced concerns about a child's development before age 2, the average age of diagnosis is still about 4.

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