An Autism Epidemic: What a Wonderful Thing
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An Autism Epidemic: What a Wonderful Thing

“Worldwide Autism Epidemic!” screams the headline. I wish it were true. If we were in the midst of an epidemic of autism, then something, or someone, would be to blame, and with a bit of sleuthing we could eliminate the problem, and prevent even more children from suffering. And, if the epidemic were man-made, we could punish the guilty. Alas, there is precious little scientific evidence to support the notion of an autism epidemic.

In order to explain, I need to define three terms: incidence, prevalence, and epidemic. Incidence is the rate of occurrence of new cases of a disorder (number of new cases of flu per week, for example). An epidemic is defined as an increase in incidence. Prevalence is a percent – in this case, the percent of persons identified with autistic spectrum disorder (ASD; the catchall term that includes autism, Asperger Syndrome, and pervasive developmental disorder, not otherwise specified). The prevalence of ASD – that is, the percent of people with an ASD diagnosis – has increased dramatically over the past decade. But that tells us nothing about incidence. Imagine that a policeman pulls you over, glances at your dashboard, and declares, “I’m giving you a ticket.” “How fast was I going?” you ask. “I don’t know,” he replies; “my radar gun is broken. But I see that you have a full tank of gas, so I’m giving you a speeding ticket.” Sounds pretty silly, doesn’t it? However, people who leap from the increase in prevalence of ASD (the so-called autism “explosion,” which is quite real) to a claim that we’re in an epidemic (increased incidence) make the same error of logic as our misguided police officer. What accounts for the increase in prevalence, and what difference does it make whether it’s a change in prevalence rather than incidence?

The increase in prevalence of ASD can be traced to broadening case definitions, and improved detection of individuals (adults as well as children) with milder forms of ASD, such as:

• FACT: Prevalence depends on our definition of what constitutes a “case.” Let’s say we wish to determine the prevalence of tall stature among adults. If we define “tall” as anyone over 7 feet, the prevalence is perhaps 1 in 1000. If we expand the definition to include anyone over 6 feet 6 inches, the prevalence jumps, to perhaps 1 in 100 – a tenfold increase in prevalence, but no one is an inch taller than before. Over the past 40 years, this is exactly what has happened with ASD. With each successive edition of the Diagnostic and Statistical Manual of the American Psychiatric Association, and the International Classification of Diseases of the World Health Organization, the criteria for diagnosis of ASD have expanded – from a uniformly severe disorder to a condition with extremely mild forms. Each time the diagnostic criteria have expanded, the prevalence of ASD has jumped – but no one is any more disabled than they were before, and babies with ASD aren’t being born any faster than before.

• FACT: Prior to 1990, the number of children with autism in the school system according to federal data was zero. Not because they weren’t there, but because it was not until 1990 that the federal government added autism as a diagnosable and reimbursable condition, as part of the Individuals with Disabilities Education Act (IDEA). Prior to IDEA, children with ASD were labeled something else – typically, “emotionally disturbed.” There was no check-box on the federal reporting forms for “autism,” and even if a school wanted to report the data, there would be no federal funds coming back. The start of the autism “explosion” coincides with the passage of IDEA.

• FACT: Now that school districts are earmarking certain educational services exclusively for children on the autistic spectrum, an incentive has been created for parents to actively seek an ASD diagnosis for their child, regardless of the child’s actual disability. The diagnosis may be a bit of a stretch in some cases, or it may be entirely justified, but we can no longer look upon school data as a passive barometer prevalence – and certainly not as a stand-in for incidence.

• FACT: As diagnostic tools and case-finding methods have improved, the prevalence of ASD among adults has risen, right along with the prevalence of ASD in children. A recent door-to-door survey in England found that 1 in 56 adult males, and 1 in 200 adult females meet criteria for ASD. Most of these adults were unknown to the social service system; all were living independently. How is it that these adults with ASD were overlooked when they were children? Another recent British study gives a hint at the answer: in a long-term follow-up study of subjects who had been diagnosed as children with “pragmatic language disorder,” nearly one third meet current criteria for ASD in adults. Conclusion: They were overlooked as children, because of overly-strict criteria for ASD in use at the time.

With all these data to account for the increase in prevalence, why are we still arguing about incidence (and the supposed epidemic)? The dirty little secret is that we don’t have any way to measure incidence of ASD. Unlike, say, birth defects or an infectious disease, we can’t stand in the delivery room and count the rate at which babies with ASD are being born, or track how many children per year “come down with” regressive ASD. The most that can be said is that there is no evidence to support the claim that we’re in an epidemic. “Explosion” (increase in prevalence)? Yes, certainly. But epidemic? No proof.

Why, then, is the notion of an epidemic so popular? In my opinion, three forces – ignorance, fear, and greed – lie at the root of the problem. The ignorance is at least partly forgivable, because most people haven’t studied medical statistics; hopefully the image of our misguided police officer writing out a citation for a full tank of gas will help people to remember that incidence (rate) and prevalence (proportion) are not interchangeable. Fear is also forgivable, because we all fear loss of control. The notion that bad things can happen for no particular reason is terrifying. Faced with a catastrophic event, some of us resort to self-blame: “The game was mine to lose, but I blew it.” Alternatively, some of us seek to blame others: one’s spouse, the doctor, or some other external agent. Guilt and blame are both easier to live with than the idea that we are living on thin ice, and that at any moment we can break through and it would be nobody’s fault (It’s probably no coincidence that most of the world’s religions seek to explain why bad things happen to innocent people).

Greed, however, is unforgivable – especially when the greedy prey upon the most vulnerable. There is nothing like a crisis to get people to open up their pocketbooks, and in my opinion there are lots of individuals – ranging from legitimate research organizations, to publicity-seeking journalists and political figures, to medical quacks, who are happy to ride the epidemic bandwagon, while raking in the cash from parents who are in a state of panic. For these crisis-entrepreneurs, an epidemic (or, at any rate, the fear of an epidemic) is indeed a wonderful thing.

An epidemic would truly be cause for hope, not fear. In 1854, the English physician John Snow broke the back of a lethal cholera epidemic. Snow did not know what caused cholera (the belief at the time was that foul air – miasma – spread disease), but he observed that all of its victims drew their drinking water from the same well. Snow removed the pump handle, and the epidemic ended. (Go to London, and you can see the infamous Broad Street pump, now a memorial to the triumph of medical epidemiology over ignorance and fear.) It would be nice if we could look forward to an equally dramatic intervention to eliminate ASD. Alas, it is not to be. Instead, we are likely to see a continuation of something akin to trench warfare, slogging inch by inch and yard by yard, taking a position here, knocking out a sniper’s nest there, but no grand stroke – nothing like removing the handle from the Broad Street pump. Even if the incidence of ASD has risen (something that can never be disproven), the lion’s share of the increased prevalence of ASD almost certainly is due to expansion of diagnostic criteria and improved case finding. I wish that those who seek their fortune by fanning the flames of fear and distrust would look elsewhere for a cause to champion. But given the emotional and financial gain to be had from the specter of an epidemic and a cover-up, I don’t expect that to happen any time soon.

James Coplan, MD, one of only a few physicians in the world who has earned specialty certification in Pediatrics, Developmental-Behavioral Pediatrics, and Neurodevelopmental Disabilities, is the founder of Neurodevelopmental Pediatrics of the Main Line ( He received his B.A. in Government Studies from Dartmouth College in 1969, his M.D. from New York Medical College in 1973, and completed his fellowship in child development at Johns Hopkins School of Medicine in 1979. He is the author of Making Sense of Autistic Spectrum Disorders (Bantam-Dell, 2010). To contact Dr. Coplan directly visit Media may contact Kristi Hughes at [email protected].

© Neurodevelopmental Pediatrics of the Main Line, 2010

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