Researchers learned autism cases continued to increase in California after the mercury-containing preservative thimerosal was eliminated from most childhood vaccines, the American Medical Association said Monday in a release.

The report, published in the AMA's Archives of General Psychiatry, said some scientists have suggested exposure to thimerosal, a preservative containing 49.6 percent ethylmercury by weight, has contributed to the upswing in reported cases of autism spectrum disorders.

Thimerosal was eliminated from most vaccines by 2001.

Dr. Robert Schechter and Judith K. Grether of the California Department of Public Health studied the prevalence of children with autism in California from 1995 through March 2007.

Using data provided by the California Department of Developmental Services, they estimated the prevalence of autism for children ages 3 to 12 years increased throughout the study period.

"Parents of autistic children should be reassured that autism in their child did not occur through immunizations," Dr. Eric Fombonne of the Montreal Children's Hospital said in an accompanying editorial.