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Autism prevalence: Now estimated to be one in 88, and the antivaccine movement goes wild

Editor’s Note: Some of you might have seen this before, but it’s an important (and timely) enough topic that I figure it’s worth exposing to a different audience. It’s been updated and edited to style for SBM. Enjoy.

If there’s one thing that I’ve learned that I can always—and I do mean always—rely on from the antivaccine movement, it’s that its members will always be all over any new study regarding vaccines and/or autism in an effort to preemptively put their pseudoscientific spin on the results. It’s much the same way that they frequently storm into discussion threads after stories and posts about vaccines and autism like the proverbial flying monkeys, dropping their antivaccine poo hither and yon all over science-based discussions.

In any case, antivaxers are also known for not respecting embargoes. They infiltrate their way into mailing lists for journalists in which newsworthy new studies are released to the press before they actually see print and then flood their propaganda websites with their spin on the studies, either attacking the ones they don’t like or trying to imprint their interpretation on ones on which they can, all before the skeptical blogosophere—or even the mainstream press—has a chance to report. So it was late last week, when vaccine-autism cranks jumped the embargo on a CDC study that announced new autism prevalence numbers. This is nothing new; it’s the antivaccine movement’s modus operandi, which makes me wonder why the various journals don’t shut off the flow. The study, of course, was announced in press conferences and a number of news stories. No doubt by now many of you have seen them. The stories I’ve seen thus far have focused on the key finding of the CDC study, which is that the prevalence of autism in the U.S. has risen to approximately 1 in 88, a finding reported in the CDC’s Morbidity and Mortality Weekly Report.

This is how the CDC came up with the new prevalence:

The Autism and Developmental Disabilities Monitoring (ADDM) Network is an active surveillance system that estimates the prevalence of ASDs and describes other characteristics among children aged 8 years whose parents or guardians reside within 14 ADDM sites in the United States. ADDM does not rely on professional or family reporting of an existing ASD diagnosis or classification to ascertain case status. Instead, information is obtained from children’s evaluation records to determine the presence of ASD symptoms at any time from birth through the end of the year when the child reaches age 8 years. ADDM focuses on children aged 8 years because a baseline study conducted by CDC demonstrated that this is the age of identified peak prevalence. A child is included as meeting the surveillance case definition for an ASD if he or she displays behaviors (as described on a comprehensive evaluation completed by a qualified professional) consistent with the American Psychiatric Association’s Diagnostic and Statistical Manual-IV, Text Revision (DSM-IV-TR) diagnostic criteria for any of the following conditions: Autistic Disorder; Pervasive Developmental Disorder–Not Otherwise Specified (PDD-NOS, including Atypical Autism); or Asperger Disorder. The first phase of the ADDM methodology involves screening and abstraction of comprehensive evaluations completed by professional providers at multiple data sources in the community. Multiple data sources are included, ranging from general pediatric health clinics to specialized programs for children with developmental disabilities. In addition, many ADDM sites also review and abstract records of children receiving special education services in public schools. In the second phase of the study, all abstracted evaluations are reviewed by trained clinicians to determine ASD case status. Because the case definition and surveillance methods have remained consistent across all ADDM surveillance years to date, comparisons to results for earlier surveillance years can be made. This report provides updated ASD prevalence estimates from the 2008 surveillance year, representing 14 ADDM areas in the United States. In addition to prevalence estimates, characteristics of the population of children with ASDs are described, as well as detailed comparisons of the 2008 surveillance year findings with those for the 2002 and 2006 surveillance years.

The bottom line is that in the cohort born in 2000 approximately one in 54 boys and one in 252 girls living in the ADDM Network communities were identified as having an autism or ASD diagnosis. One thing that we should be clear on right here because it’s right in the report is that ADDM Network sites do not make up a nationally representative sample, which means that these prevalence numbers can’t be generalized to the whole U.S.

Before I dig into the report a bit more and discuss the reaction of the antivaccine movement to it, let’s first note one thing that you will not (and I did not) see in the various hysterical reactions to the study that I’ve seen thus far. You will not see any of the usual suspects emphasize mercury in the thimerosal preservative that used to be used in vaccines in the context of the report (although one does foolishly mention it, see below). The reason is obvious. If autism prevalence is still rising (or even if it’s staying the same), it’s yet another death blow to the hypothesis that mercury in vaccines causes autism. After all, thimerosal was removed from nearly all pediatric vaccines back in 2001, but the process began in 1999 after the CDC and the American Academy of Pediatrics’ vaccine advisory committee advised that thimerosal be removed from childhood vaccines. By 2000 the process was under way. If mercury in vaccines were a cause of autism, we’d expect to start to see a decline in autism prevalence. Even if the cause of this apparent increase in autism prevalence is better detection, broadening of the diagnostic criteria, and increased awareness, this report is not good news for those who believe that mercury in vaccines cause autism.

Now that that one point is out of the way, let’s see what the various antivaccine groups are saying about the report. For instance, the Canary Party, which seems to be tightly affiliated with Generation Rescue and the antivaccine crank blog Age of Autism, jumped the gun the day before the report was released and declared:

This week, the Canary Party expects CDC to announce a new autism prevalence rate of 1 in 88. As boys are diagnosed with autism at four times the rate of girls, this translates to 1 in 48 boys. That new rate would be an increase from the previous 1 in 110 reported two years ago by the CDC’s ADDM (Autism Developmental Disabilities Monitoring) Network. This would only be the latest uptick in the autism rate reported by CDC, as the disorder was diagnosed in 1 in 10,000 in the 1960s, and the rate was virtually zero before 1930.

This first paragraph reveals a depth of ignorance that surprises me even from antivaccinationists. There’s a reason that autism prevalence was “virtually zero” before 1930, and that’s because autism wasn’t defined as a distinct clinical entity until 1943, when Leo Kanner published his seminal paper describing the characteristics of autism. While it’s true that the word “autism” was used as early as 1911, when Eugen Bleuler, a Swiss psychiatrist, used the term to refer to one group of symptoms of schizophrenia, the word has meant different things throughout the years, which is why such historical comparisons are almost meaningless before the early 1990s. Ironically, this little bit of history gives me the lead-in to introduce the biggest question about this newly reported prevalence statistic: Is this a “real” increase in autism and ASD diagnoses, “real” meaning that biologically there is a real increase; i.e., it can’t be explained by reasons other than biology? Or is it the increase in autism and ASD diagnoses due to improved diagnosis, screening, and awareness? The antivaccine movement has put all its money on a real increase. The reason is simple. Without a “real” increase in autism prevalence, there is no vaccine-autism hypothesis because in that case there isn’t even correlation to confuse with causation. You can see this in Ginger Taylor’s list or rhetorical questions:

How did we go from one in 10,000 children born 50 years ago being diagnosed with autism to 1 in 88 diagnosed today? Why do the Centers for Disease Control refuse to call the avalanche of autism diagnoses in the U.S. anything more than an “urgent public health concern?” Why is the federal agency downplaying a national emergency with special wording created just for autism – Urgent Public Health Concern – a label that is not used to describe any of the thousands of other disorders and conditions the agency tracks? When dozens of published research papers and multiple congressional hearings have shown that the primary causes of autism are environmental, and include vaccines and their components, why has CDC failed to offer any advice to new parents on how to decrease the chance of a child developing autism? Why has CDC chosen not to even attempt to identify which children are the subset vulnerable to these environmental exposures so that they can be handled with greater care?

Note that “environmental exposure” is code for “vaccines” among antivaccinationists. If that isn’t clear to my regular readers by now, it never will be. The above paragraph makes it as clear as clear can be. SafeMinds echoes the same theme in its press release:

  • Growth in autism rates this dramatic can only be driven by environmental factors.
  • The majority of cases of autism are caused by environmental exposures coming before and/or after birth. This makes them preventable. Until we do a better job of eliminating the soup of toxic pollution our children are exposed to, increases in prevalence like this will likely continue. Autism has been associated with mercury, pesticides and air pollution.

This is a complicated issue, as you might imagine, as various bloggers, such as Steve Novella, have pointed out. However, this part is relatively simple. The antivaccine movement assumes that the huge increase in diagnoses indicates a real increase in the prevalence of autism. They do this because the vaccine-autism hypothesis needs an “autism epidemic” in order to claim correlation between vaccines and autism, as tenuous and biologically implausible as the correlation might be. The more its members can gin this up as some sort of “public health emergency,” the better the chance they can convince the credulous that there is an autism “epidemic.” It might. It might not. What is being almost willfully ignored here is the simple fact that the number of diagnoses of a condition does not necessarily accurately reflect the “true” prevalence in a given population. This is particularly true for a condition like autism and ASDs, where the diagnostic criteria are not nearly as “hard” as in other conditions. In fact, you can see just what I’m talking about if you look at the reaction of the antivaccine movement to the proposed DSM-5, which in its current form tightens the diagnostic criteria for autism and ASDs. You might remember a couple of months ago that the antivaccine crankosphere was in a real lather over the proposed changes, claiming they are a “conspiracy” to hide the autism epidemic (and thus, of course, to exonerate vaccines as its cause) by changing the diagnostic criteria. (Whenever diagnostic criteria are tightened, usually the number of diagnoses for the condition covered by those criteria decreases.) Add to that the fact that there are now a lot of government benefits that depend on a diagnosis of autism or ASD, and there are lots of reasons why the antivaccine movement needs to spin this report to its purpose.

To try to put the results in context, the CDC published an accompanying commentary from the director of NIMH, Thomas Insel, that describes why these results do not necessarily indicate a “true” increase in autism in the population and why it could very well just mean we’re picking up more autism. After invoking a study from South Korea with a high autism prevalence, as well as a British study that found a pretty constant prevalence among all age ranges, suggesting that prevalence hasn’t changed much over the last 50 or 60 years, comparing it to a California study that concluded that only 26% of the increase can be accounted for by better awareness and detection, Insel writes:

This takes us back to the central question: has the number of children with ASD increased or not? Total population epidemiological studies suggest much or all of the increase is due to better and wider detection. Studies of administrative and services data suggest that better detection cannot fully explain the profound and continuing increase. Are we seeing more affected or more detected? The question is vitally important, but there is not one, simple answer just as autism is not a single, simple disorder.

Antivaccinationists argue that increased diagnosis and screening alone can’t explain such a large increase in genetic diseases; hence, autism is not a genetic condition but rather due to environment (cough, cough, vaccines). However, they are quite wrong in the premise behind their argument. If there’s a single rule I’ve learned over the last couple of decades, it’s that whenever a mass screening programs for a condition is undertaken, more people will acquire that diagnosis—sometimes many, many more. For example, let’s look at cancer, specifically breast cancer, since that’s what I know best in medicine. I did a talk a while back part of which addressed this very issue; so I had to look up the data. Specifically, I looked at ductal carcinoma in situ (DCIS), which is a premalignant precursor of breast cancer. Basically, it’s cancerous cells that haven’t broken out of the breast ducts yet. Back in the early 1900s, DCIS was rare because by the time it grew large enough to be a palpable mass, it almost always had become invasive cancer. Enter mammography. Now, thirty years or so after mass mammographic screening programs began, DCIS is common. Indeed, approximately 40% of breast cancer diagnoses are in fact DCIS. Indeed, a recent study found that DCIS incidence rose from 1.87 per 100,000 in the mid-1970s to 32.5 in 2004. That’s a more than 16-fold increase over 30 years, and it’s pretty much all due to the introduction of mammographic screening. Think of something like hypercholesterolemia. Fifty years ago, it was an uncommon diagnosis. Changes in diagnostic criteria and screening have lead to an explosion in diagnoses, with large proportions of the population being on statins. Heck, as I pointed out just the other day, before the 1920s doctors didn’t routinely measure systolic/diastolic blood pressure ratios; so there were few, if any, cases of hypertension because doctors weren’t looking for it.

In other words, if you don’t look for something, you won’t find it, and if you do look for something, you will find a lot more of it than you expected. It is quite possible that that is what’s happening with autism, but such a narrative doesn’t fit into the vaccine-autism idea. The antivaccine movement needs an increasing apparent autism prevalence. It needs it so bad that SafeMinds will even post hysteria like this:

The prevalence of autism is rising at about 12% a year. That means:

  • The number of children with autism will double every 6 years.
  • In 5 years, autism could affect 1 in 50 children or 1 in 31 boys.
  • There will be at least one child with autism in every classroom in America.
  • Let’s consider what that means in numbers of children affected:
  • Approximately 4 million babies are born each year in the United States. That means that each year, at current rates, 45, 454 children will be diagnosed with autism. That also means:
  • In 5 years, if we don’t find a cause and rates continue to increase, 80,000 children per year will be diagnosed with autism. How many children have to be affected before our country takes action? 5 percent? 10 percent?
  • Can anyone with a conscience claim that this isn’t an epidemic?
  • SafeMinds believes that most cases of autism are preventable and treatable. We demand action to protect our children.

This is fear-mongering, pure and simple. It also assumes that autism prevalence can continue to increase exponentially. No condition or disease can do that; incidence and prevalence always eventually level out and reach an equilibrium. If they didn’t, then sooner or later 100% of a population would be affected. In any case, pay special attention to the last bullet point. This is in reality an appeal to divert scarce research dollars away from scientifically promising avenues to the scientifically discredited vaccine-autism hypothesis (indeed, later in the press release, SafeMinds states emphatically in its press release that vaccine studies “cannot be taken off the table.” To support this assertion, SafeMinds trots out a hoary host of antivaccine tropes, including the Poul Thorsen gambit, the “no studies” (that I like) gambit, the “too many too soon” gambit, and several others. Amusingly, SafeMinds even trots out the mercury gambit, even though, as I described above, if anything the CDC report should put the final nail in the hypothesis that mercury in the thimerosal preservative in vaccines causes autism. The Canary Party’s press release echoes many of the same antivaccine tropes, particularly the spurious claim that vaccines safety is inadequately tested.

In fact, the antivaccine movement is going all out. For example, the Canary Party is taking advantage of the press given to autism episodes today, World Autism Day, to hold a press conference demanding “action.” What “action” do they demand? Well, here’s a sample of its announcement of the press conference, which is to be streamed live:

The organizations call for three urgent action steps:

  1. Secretary Sebelius should declare a national health emergency and order the NIH and CDC to shift their research focus to prevention efforts, especially investigation of long overlooked environmental factors.
  2. The Government Accounting Office should initiate a study of past research funding that has ignored environmental causes. We need to understand whether this was the result of lobbying to avoid possible liability that might be uncovered with examination of environmental triggers.
  3. The U.S. House of Representatives Government Reform Committee should initiate promised hearings as soon as possible on the failure of federal health agencies in appropriately responding to this epidemic. It has been about ten years since this Committee examined the role of the federal authorities in the autism epidemic.

We can think of no other instance of any comparable epidemic that has gone on so long without Congressional oversight. Grassroots organizations represented at the press conference: Age of Autism, AutismOne, Autism Action Network, Autism File, The Canary Party, Center for Personal Rights, The Coalition for Safe Minds, Elizabeth Birt Center for Autism Law and Advocacy, Focus Autism, National Autism Association, Talk About Curing Autism.

Interesting that Generation Rescue isn’t listed as supporting the press conference. Neither is Barbara Loe Fisher’s NVIC. Maybe they recognize a loser when they see one, although Age of Autism is for all intents and purposes a wholly owned subsidiary of . In any case, notice the harping on “environmental” factors. Remember what I’ve said many times before. In antivaccine lingo, “environmental factors” is code for “the vaccines done it,” and antivaccinationists are milking these CDC numbers for all they’re worth.

So is the “real” prevalence of autism and ASDs increasing? Damned if I know. I do, however, know that, even if it is, it’s not an “epidemic” any more than DCIS is an “epidemic.” Diagnostic substitution, increased screening and awareness, all topped off with strong incentives to place the diagnosis of autism or ASD on children contribute to an apparent skyrocketing autism prevalence. In reality, as the South Korean and British studies strongly suggest, if there is a “real” increase, it’s probably a relatively small one. Show me strong evidence of a “real” increase, and I’ll change my mind. Failing that, finally I also know that the antivaccine movement is so invested in the concept of an “autism epidemic” because it supports its delusion that vaccines cause autism that no study and no amount of data will ever convince them otherwise.

Posted in: Neuroscience/Mental Health, Public Health, Science and the Media, Vaccines

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