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Vaccines Unrelated to Increase in Developmental Disorders

Canadian researchers rule out link between mercury-containing vaccines and autism

THURSDAY, July 6 (HealthDay News) -- Exposure to ethylmercury (thimerosal)-containing childhood vaccines is unrelated to increasing rates of pervasive developmental disorders (PDDs) such as autism and Asperger syndrome, according to a study in the July issue of Pediatrics.

Eric Fombonne, M.D., of Montreal Children's Hospital in Quebec, Canada, and colleagues surveyed 27,749 children born between 1987 and 1998 for PDD and thimerosal exposure.

The researchers found that PDD rates started to increase before the change from medium thimerosal exposure (1987-1991) to high exposure (1992-1995) and continued to rise at the same pace after thimerosal was excluded from Canadian vaccines in 1996. They also found that the PDD incidence was significantly higher in thimerosal-free children than in thimerosal-exposed children (82.7 per 10,000 versus 59.5 per 10,000).

"Using logistic regression models of the prevalence data, we found no significant effect of thimerosal exposure used either as a continuous or a categorical variable. Thus, thimerosal exposure was unrelated to the increasing trend in pervasive developmental disorder prevalence," the authors state. "Factors accounting for the increase include a broadening of diagnostic concepts and criteria, increased awareness and, therefore, better identification of children with pervasive developmental disorders in communities and epidemiologic surveys, and improved access to services," they conclude.

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