California Experiencing Unusual Increase in Autism Diagnoses

Intrigued by the increasing number of autistic children in California, researchers set out to determine what factors could be to blame. After all, it’s quite surprising to see how the state’s autistic prevalence has gone from fewer than nine in 10,000 for children born in 1990 to more than 44 in 10,000 for children born in 2000. Initially, study authors speculated that the increase might have something to do with how the condition was diagnosed or counted, but the UC Davis M.I.N.D. Institute study shows that these factors are not relevant.

The study, published in the January 2009 issue of Epidemiology, “correlated the number of cases of autism reported between 1990 and 2006 with birth records and excluded children not born in California” using the “Census Bureau data to calculate the rate of incidence in the population over time and examined the age at diagnosis of all children ages two to 10 years old.” Researchers eliminated migration as a potential cause, and also determined that only 24% of the increase could be attributed to being diagnosed at an earlier age. In addition, researchers pointed out that California’s increasingly diverse population is not a factor because autism rates are fairly similar in all ethnic groups. Therefore, the study’s authors suggest that “research should shift from genetics to the host of chemicals and infectious microbes in the environment that are likely at the root of changes in the neurodevelopment of California's children.”

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