No, the autism prevalence did not go down in Denmark after the removal of thimerosal
Posted Feb 22 2013 9:11pm
Once there was an open question of whether the thimerosal containing vaccines, previously used for infants in the U.S. could be contributing to the increase in autism diagnoses being reported. Even with multiple studies showing no increased risk due to thimerosal exposure, there is still a group who not only believes in the mercury-induced epidemic, but they believe that there has been a concerted effort on behalf of the U.S. government and other groups to hide this “fact”.
An email obtained through a freedom of information act (FOIA) request is often cited in online discussions of not only the “fact” that the mercury-induced-epidemic is real, but that the government conspiracy is real. The email reportedly was made by one of the authors of a study from Denmark . The authors had used a sort of natural experiment: Denmark had phased out thimerosal from vaccines in the early 1990′s. They reported that the prevalence of autism continued to increase even with the phase out, thus indicating that thimerosal was not the driving force behind the increase.
The study, by Madsen, et al., was published in 2003. An email obtained by FOIA reportedly shows the authors removing data for the final years of the study period:
I need to tell you that the figures in the manuscript do not include the latest data from 2001….But the incidence and prevalence are still decreasing in 2001.
Sounds alarming, doesn’t it? Data which supposedly shows that autism rates actually dropped following the removal of thimerosal was removed from a paper. Well, I think they should have included the data, a possible explanation and done a follow-up study. That said, the statement really doesn’t bother me. Why? A few reasons but mainly because the data are clear that autism prevalence did continue to go up in Denmark. And much of that data are below.
First, what was the prevalence in the 1990s? Here’s a study from 2007. They were using data where from 2004 (followup through 2004):
Yes, they are showing ASD prevalence dropping in the 1990′s, which should be an admission that the prevalence went down after the removal of thimerosal! I guess they forgot to censor that paper. While ASD prevalence seems to be going down, Childhood Autism is relatively flat. Why would that happen, do you think? Here’s one reason: average age of diagnosis for autistic disorder (childhood autism) is lower than that for the other ASD’s. While autism is not as obvious as many would have us believe, childhood autism *is* more obvious than the other ASD’s (and even with that it gets missed). Consider 1998-1999. That’s only 5 years or so until the followup date from the study: 2004. Average age of diagnosis for ASD in Denmark was about 5 years . So, about 1/2 of the ASD kids born 1998-1999 were not diagnosed at the time of the study. More of the ASD kids born in 1995-1996 and even more of those from 1994-1995. So, what looks like a declining prevalence is most likely just an artifact of how many years of follow-up there were from birth to study date.
I’d say it is even more than “looks like”. Consider the studies below. These are the papers I could easily find that give autism prevalence values for Denmark. I give the title, with a link to pubmed, the year of the study, the birth cohorts reported and the prevalence.
Autism prevalence in the 1990′s?
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Birth cohort 1990-1996. Prevalence 0.26%
Autism prevalence for cohorts including kids born after 2000? More like 1%. Consider this first paper:
But there are more. The cohorts don’t always match between studies, and we don’t have individual years for kids born 2000 and later. But the prevalence is repeatedly reported as above the 0.26% found for the 1990′s.
In other words, the prevalence continued to go up.
The more early birth cohorts a given study uses, the lower the average prevalence. The more years included post 2000, the closer the prevalence is to 1%.
Sure, it would be great if we had data for prevalence by individual birth year going to 2000 and beyond. But there’s enough data above to make it clear that the autism prevalence in Denmark did not go down after 2000. Quite the contrary. Similarly, measures of autism prevalence in my home state, California, have continued to go up even after thimerosal was removed.
The idea that thimerosal caused an autism-epidemic is just not consistent with the facts. The same data people used over and over to make the argument that thimerosal causes autism–the various autism prevalence estimates–don’t support the idea any more. Thimerosal went away, autism prevalence continued to climb.
So I’m just not swayed when I read people write about how the autism prevalence went down in Denmark with the removal of thimerosal. It didn’t go down. It is sad that people are being misled to think there is still some substance to the mercury-epidemic idea. Cherry pick one email out of how many FOIA’d documents, present it out of context and play it up as something real–while ignoring the evidence that is right in front of you. This is not treating the autism community with respect. This is misleading people.