More than one of every 100 local students have autism, a rate that has more than tripled during the last decade, according to new figures from the California Department of Education.
About 3,830 students in the four-county area were autistic in December 2011, up by 450, or 13 percent, from 2010. The rise occurred even as total enrollment in the region stayed flat.
Statewide, the number of autistic students rose by 6,000, or 9 percent, to almost 72,000. For perspective, the number of autistic students in California now outnumbers the total enrollment of Elk Grove Unified, the region's largest school district.
Theories for the rise, which is a nationwide phenomenon, include improved autism screening, broader definitions of the condition and a genuine increase in autism cases.
A widely-publicized University of California study concluded that changes in diagnoses patterns alone cannot explain the rise in the disease. Instead, the study postulated that environmental factors were partially to blame and called for more study of the effects of viruses, pesticides, chemicals and other substances on the development of autism.
This chart shows the number of students with autism in the four-county region over the last decade.