Posted on 09/03/2003 8:41:09 PM PDT by Pan_Yans Wife
A new study from Denmark tends to discount widely held fears that a mercury-based preservative formerly used in childhood vaccines may be responsible for the rapid rise in diagnoses of autism.
In the study, published this week in the journal Pediatrics, a team of Danish doctors counted all the diagnoses of autism in the country from 1971 to 2000. They found no decrease after 1992, when Denmark became the first country in the world to ban the preservative, thimerosal.
Rather, autism diagnoses continued to skyrocket on the same trajectory that began in the late 1980's, rising from less than one case per 10,000 Danish youngsters in 1990 to more than three a decade later.
American vaccine makers began phasing out thimerosal in 1999, and a similar American study is planned, said Dr. Robert L. Davis, a professor of epidemiology and pediatrics at the University of Washington.
But Dr. Davis added that evidence from the Danish study was clear-cut. "If you remove cars from highways, you'll see a marked decrease in auto-related deaths," he said. "If thimerosal was a strong driver of autism rates, and you remove it from vaccines, you should have seen some sort of decline — and they didn't."
Other American experts also praised the findings. Dr. Neal A. Halsey, director of the Institute for Vaccine Safety at Johns Hopkins, called the report "helpful and important."
And Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University in Nashville, said the study "adds to the whole mosaic of studies that have addressed this." He noted, "Each is imperfect, but they all add up to this theme: thimerosal is not the culprit."
But Safe Minds, a New Jersey parent group that argues that mercury may be the culprit if children are genetically hypersensitive to it, attacked the study's methods. It said the researchers "artificially boosted" the number of cases by adding outpatients and those at a large Copenhagen clinic to earlier inpatient figures. The group also said that two scientists in the study worked for the Danish vaccine manufacturer, suggesting a conflict of interest.
Dr. Kreesten Meldgaard Madsen of the Danish Epidemiology Science Center, who led the new study, replied that in Denmark a diagnosis of autism must be made by a psychiatrist and registered with the health system, which categorizes any patient who even visits a hospital for a test as an "inpatient." To make sure, Dr. Madsen said, he excluded the outpatients — and still found the same upward trend in autism diagnoses.
Danish vaccines are not made by profit-seeking corporations but by the government health agency, the State Serum Institute, which he compared to the Centers for Disease Control and Prevention in the United States. He said he invited the two scientists onto his team because they provided the government's data.
"We could have had funding from private companies that make vaccine," Dr. Madsen said. "But I didn't want it."
Thimerosal fell under suspicion because the first symptoms of autism — introversion, unresponsiveness and repetitive behavior — often appear in the same years that children get most of their shots.
Dr. Madsen said he was skeptical that thimerosal could be the cause. It is 50 percent ethyl mercury by weight, but the symptoms of mercury poisoning are very different. Victims often have difficulty walking and forming words, restricted vision, deadened nerves, psychosis or depression and slightly shrunken brains. Children with autism typically have larger-than-average brains, a tendency to echo words or be silent, hypersensitivity to noise, social aloofness and no vision problems.
Thimerosal kills bacteria and fungi, and banning it made vaccines more expensive, because more come in one-dose bottles or have shorter shelf lives.
Like many other researchers, Dr. Madsen said he believed that autism started in utero.
The syndrome was described and named only in 1943, "and my guess is that diagnosis plays a significant part," Dr. Madsen said.
As pediatricians became more aware of autism in the 1990's and behavioral tests were developed, he said he believed that children once considered odd but normal, as well as children for whom the diagnosis would once have been mental retardation, were classified as autistic.
I've always believed this to be the main reason that cases of autism have seemingly increased.
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