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Friday, 21st January 2005
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Over the past 20 years, there has been speculation about a
connection between immunizations and an increase in autism.
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ROCHESTER, Minn. -- Over the past 20 years, there has
been speculation about a connection between immunizations
and an increase in autism. However, a study by Mayo Clinic
researchers published in the January issue of Archives of
Pediatrics and Adolescent Medicine suggests the increase
may be due to improved awareness, changes in diagnostic
criteria and availability of services, not environmental
factors or immunizations.
"This study is the first to measure the incidence -- the
occurrence of new cases -- of autism by applying consistent,
contemporary criteria for autism to a specific population over a
long period of time," says William Barbaresi, M.D., a Mayo Clinic
developmental pediatrician and one of the study authors. "In doing
so, the study accounts for improvements in the diagnostic criteria
for autism, the medical community's improved understanding of this
disease and changes in federal special education laws."
The study found that the increase in the incidence of autism in
Olmsted County, Minn. coincided with broadening of the diagnostic
criteria for autism and new federal special education laws including
autism as a disability category. Both events occurred many years
after immunizations were mandated for school entry. Broader, more
precise diagnostic criteria for autism were introduced in 1987.
Prior to these new criteria, children with autism may have been
given less precise diagnoses such as "developmental delay" or
"mental retardation," and children with milder symptoms of autism
may not have been identified at all. The 1991 federal special
education laws improved the availability of educational services for
children with autism.
The study used data from the Rochester Epidemiology Project, a
database of all inpatient and outpatient records in Olmsted County,
Minn. The database diagnoses are indexed for computerized retrieval,
allowing researchers to identify subjects with any developmental
disorder. Researchers found 3,000 children with at least one of 80
diagnoses related to autism. Of the 3,000 children, 124 actually met
the current diagnostic criteria for autism. Reviewing the medical
and school history of this group showed that the incidence of autism
was stable until 1988-1991, then increased after new laws and new
diagnostic criteria were implemented.
Sources
Mayo Clinic.
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