Autism cases continued to increase in the US state of California after the mercury-containing preservative thimerosal was eliminated from most childhood vaccines in 2001, according to a new report in which doctors studied the prevalence of children with autism in California from 1995 through March 2007.
“The estimated prevalence of autism for children at each year of age from three to 12 years increased throughout the study period,” the authors reported. Per 1,000 children born in 1993, 0.3 had autism at age three, compared with 1.3 per 1,000 births in 2003. The highest estimated prevalence- 4.5 cases per 1,000 births- was reached in 2006 for children born in 2000.
“Although insufficient time has passed to calculate the prevalence of autism for children six years and older born after 2000, the prevalence at ages three to five years has increased monotonically for each birth year since 1999, during which period exposure to thimerosal has been reduced,” the doctors also reported.
As well as analysing the prevalence of autism by birth year, researchers also examined the rate among children aged three to five years based on quarterly reports. Prevalence increased each quarter from January 1995 through March 2007, including after 2004, when the researchers estimate that exposure to thimerosal during infancy and early childhood declined. Over the same time period, the rate of all developmental disabilities also increased, but at a slower rate.