CHICAGO (Reuters) — US researchers have identified ten locations in California that have double the rates of autism found in surrounding areas, and these clusters were located in neighbourhoods with high concentrations of white, highly educated parents.

Researchers at the University of California Davis had hoped to uncover pockets of autism that might reveal clues about triggers in the environment that could explain rising rates of autism, which affects as many as one in 110 US children.

But the findings likely say more about the US health care system than the causes of autism, said researcher Irva Hertz-Picciotto of UC Davis' MIND Institute, whose study will be released online today in the journal Autism Research.

Advocacy groups have been clamouring for treatment options and for better research to show what might be causing an apparent increase in autism cases.

Hertz-Picciotto and colleagues used a research technique that has been effective at identifying cancer clusters.

"This kind of analysis sometimes turns up clues about environmental factors," she said in a telephone interview.

The researchers looked at about 2.5 million births recorded in California from 1996 through 2000. About 10,000 of those children were later diagnosed with an autism spectrum disorder, according to the state's department of developmental services.

Using data from birth records, the team found a strong link between parental education and the high rates of autism.

"In this particular case, we found 10 clusters of autism across the state of California. When we looked further, we discovered virtually all of them were areas where there was a higher level of education among the parents who were giving birth in those years," Hertz-Picciotto said.