From Scientific American:
California scientists have discovered clusters of autism, largely in the Los Angeles and San Francisco areas, where children are twice as likely to have autism as children in surrounding areas. The 10 clusters were found mostly among children with highly educated parents, leading researchers to report that they probably can be explained by better access to medical experts who diagnose the disorder. Because of the strong link to education, the researchers from University of California at Davis said the new findings do not point to a localized source of pollution, such as an industry, near the clusters.
“I suspect access to services plays the major role,” said Irva Hertz-Picciotto, senior author of the study published Tuesday in the journal Autism Research.