A researcher studying rates of pervasive developmental disorder among children in the Canadian province of Quebec says there is no link between the prevalence of the disorder—of which autism is one type—and a mercury-based preservative once used in childhood vaccines.
Dr. Eric Fombonne, the director of pediatric psychiatry at the Montreal Children’s Hospital of the McGill University Health Center, studied 27,749 children born in Quebec from 1987 to 1998. Of those children, 180 were diagnosed with a pervasive developmental disorder, or PDD.
The numbers work out to a prevalence of one child in 155, an estimate “highly consistent with what we’ve seen in previous studies,” Dr. Fombonne said in an interview.
The rates of PDD prevalence rose over the time period studied, and continued to rise even after the mercury-based preservative, thimerosol, was removed from childhood vaccines in Quebec in 1996, Dr. Fombonne said. Children in Quebec received a dose of mercury in their childhood vaccines comparable to the amount received by children in the United States, he said.
“For the U.S. debate, this is very informative,” he said, referring to the long-running controversy over what some people suggest is a link between mercury exposure and autism.
Dr. Fombonne also measured PDD prevalence against the rate of vaccination for measles, mumps, and rubella. In the United Kingdom, a published report that linked the measles vaccine to autism caused some parents to refuse to have their children vaccinated. The MMR vaccine has never contained thimerosol.
The MMR vaccination rate dropped slightly in Quebec over the course of the study, but PPD rates continued to rise, eliminating a link between the measles vaccine and autism, Dr. Fombonne said.
The findings were published in the July issue of Pediatrics, the journal of the American Academy of Pediatrics.
In the report, Dr. Fombonne suggests that rates of PDD may be going up as doctors become more adept at diagnosing disorders such as autism and Asperger’s syndrome, another type of pervasive developmental disorder. And, though he said that his study and many others suggest there’s no link between autism and thimerosol, he cannot categorically rule out the suggestion that there is some environmental basis to autism and similar disorders.
“I’m open to looking at a new hypothesis,” he said.
A version of this article appeared in the July 26, 2006 edition of Education Week