Researchers at UC Davis have identified 10 locations in California where the incidence of autism is higher than surrounding areas in the same region.
Most of the areas, or clusters, are in places where parents have higher-than-average levels of education.
The clusters are found primarily in the high-population areas of Southern California and, to a lesser extent, in the San Francisco Bay Area. The researchers said that, while children born within the clusters during the study period were more likely to be diagnosed with autism, the majority of the state's children with autism were born in adjacent areas outside the clusters.
For the rigorous study, published online today in the journal Autism Research, scientists examined nearly all of the approximately 2.5 million births recorded in California from 1996 through 2000. About 10,000 children born during that five-year period were later diagnosed with an autism, according to the state Department of Developmental Services.