Autism Increase Not Due to Better Diagnosis

Irva I. Hertz-Picciotto, Ph.D.
University of California Davis
NIEHS Grants P01ES011269 and R01ES015359

A study conducted by NIEHS-funded researchers at the University of California Davis found that the seven- to eight-fold increase since 1990 in the number of children born in California and later diagnosed with autism cannot be explained by changes in how the condition is diagnosed or counted. The researchers also conclude that the trend is not slowing and suggest that the research focus should shift from genetics to the multitude of chemical and infectious agents in the environment that could be involved in the rapid rise in the incidence of autism.

The results of the investigation show that the incidence of autism by age six in California increased from fewer than 9 cases per 10,000 children born in 1990 to more than 44 per 10,000 children born in 2000. Migration patterns and changes in diagnosis were ruled out as possible reasons for the increase. The results show that less than one-tenth of the increase can be attributed to the inclusion of milder cases of autism.

These researchers are currently involved in two large studies aimed at discovering possible environmental factors and gene-environment interactions responsible for autism. They are focusing on the potential effects of metals, pesticides, and infectious agents on neurodevelopment.

Citation: Hertz-Picciotto I, Delwiche L. The rise in autism and the role of age at diagnosis. Epidemiology. 2009 Jan;20(1):84-90.