How Common Is Autism?

The clinical term for autism is autism spectrum disorder (ASD). It’s a neurodevelopmental disorder — a condition you’re born with. Basically, changes in the brain cause people with autism to learn, behave, communicate or interact differently from their neurotypical counterparts.

“It really is a spectrum,” says developmental pediatrician Carrie Cuffman, MD. “No two people with autism are alike.” Some autistic individuals’ symptoms are barely noticeable, while others are severely impaired by them. That diversity of experience makes identifying the condition tricky, to say the least.

Even so, ASD diagnoses are on the rise. Dr. Cuffman explains why.

Why have autism diagnoses increased?

Autism diagnoses have been climbing consistently over the past 20 years, both in the U.S. and around the globe.

The most recent data from the U.S. Centers for Disease Control and Prevention (CDC) underscore how common autism is. They report that 1 in every 36 children has ASD. They broke it down by sex, too. Their estimate: approximately 4% of boys and 1% of girls are autistic. (Unfortunately, they didn’t collect data regarding gender identity, so we have no insight into ASD prevalence on that score.)

That’s a pronounced increase, but it’s not a sign of an “autism epidemic.” While it’s possible that there’s been a slight increase in the number of people who have the condition, most of that growth can be explained by changes in ASD diagnosis and treatment.

Awareness and accommodations

In many respects, the rise in ASD diagnoses over the past few decades is good news. It’s a sign that awareness of the condition has gone up.

“You’re much more likely to bring your kid into your provider and ask about autism when you know what it is,” Dr. Cuffman explains, “So we’re diagnosing more kids — and doing it earlier than we used to.” And children aren’t the only ones benefitting. Many individuals who reached adulthood without ever being worked up for the condition are finally getting diagnoses, decades later.

But it’s not just public awareness (and acceptance) that’s fueling the rise in diagnoses: It’s also the fact that an ASD diagnosis may actually help children now, in ways it didn’t in previous generations.

“Another explanation for the increasing numbers is that more services are available,” Dr. Cuffman adds. “It's worth getting your kid diagnosed now because there are more treatment options out there that you can access.” We’re talking speech and language therapy. Social skills groups. Specialists in developmental nutrition and psychiatry. Simply put: There’s a wide range of supportive services out there to help autistic children thrive. Many of these services either didn’t exist or weren’t accessible in previous decades.

“Parents wouldn’t bother to have their kids evaluated if there weren’t accessible treatments,” she notes. “Now, having a diagnosis means you’re more likely to get help for your child.”

Changes to the diagnostic criteria

The rise in ASD cases isn’t entirely the result of the growing understanding of the condition or the incentive to get a formal diagnosis. The numbers also went up because what counts as ASD has changed over time.

2013 saw the publication of the 5th edition of the Diagnostic and Statistical Manual (DSM-5) — the American Psychiatric Association’s (APA) reference text. This book classifies and sets out all of the diagnostic criteria for mental health and brain-related conditions.

Before 2013, ASD didn’t exist. Instead, there were several developmental disorders in the DSM that had similar characteristics:

• Autism.
• Pervasive developmental disorder.
• Asperger’s syndrome.
• Childhood disintegrative disorder.

It was, in a word, confusing. The diagnoses were mutually exclusive, meaning that if a child had some — but not all — of the symptoms for several of these conditions, the provider needed to choose the diagnosis that best fit the child. The same was true of attention-deficit/hyperactivity disorder (ADHD). It used to be the case that you couldn’t diagnose somebody with ASD and ADHD.

The result: Providers mis- or undiagnosed lots of children. The diagnostic criteria had a particularly negative impact on girls, kids with mild symptoms and kids with other, more obvious intellectual disabilities.

In 2013, the APA changed its framing.

“All of these conditions now fall under the umbrella of autism spectrum disorder,” Dr. Cuffman explains. In other words, those four diagnoses no longer exist. The diagnostic criteria for ASD being as expansive as it is means fewer children fall through the cracks. It also means that the number of people who qualified as autistic grew overnight.

In thinking about the changing clinical standards, there are a few things to keep in mind:

• Many people who grew up with the older diagnoses still identify with that terminology. For example, some people who were originally diagnosed with Asperger’s — while now classified as having ASD — still refer to themselves as “aspies.”
• The DSM-5 is a reference text for mental health professionals practicing in the U.S., but providers around the world use it, too (it’s available in 18 different languages). Still, depending on the country, people living outside the U.S. may not use the same terminology or diagnostic criteria.

Other reasons ASD is on the rise

The vast majority of the increase in ASD cases can be explained by the changing diagnosis and growing public awareness of the condition. But Dr. Cuffman and other researchers concede that there may be at least some real-world increase. If there is, it’s likely due to a combination of factors like:

Genetic factors

Unlike conditions like Down syndrome, which are the result of a single, specific genetic difference, there are over 1,000 potential genetic changes that can result in ASD.

Autism can also be hereditary. That matters because more autistic people than ever before are getting the support they need at a young age. Those early interventions can have a big impact on quality of life and make it easier to have relationships — and children — as adults.

Environmental exposure

“It’s clear that toxic insults to the health of a fetus or newborn are big risk factors for autism,” Dr. Cuffman notes. That exposure may happen in utero or shortly after birth. Here are a few examples:

• Issues with oxygenation (the fetus not getting enough air).
• The birthing parent having an infection.
• Exposure to toxic substances like alcohol, opioids or thalidomide.
• Interacting with polluted air, water or soil.

Modern medicine

There are certain variables that researchers say raise your likelihood of having autism. A lot of them have to do with the circumstances of a child’s birth. ASD is more common when one or more of the following are true:

• Maternal age is over 35.
• Paternal age is over 40.
• A baby is preterm.
• A pregnancy has significant complications.
• The child’s birth weight is low.

You may be noticing a pattern here: Medical advances mean that children who may not have survived in the past are alive and well today. The result is an increase in the prevalence of neurodevelopmental disorders.

Don’t blame vaccines

There’s one thing we know for sure isn’t causing the increase in ASD: vaccines. In 1998, a doctor and anti-vaccination activist named Andrew Wakefield published a now-discredited paper in The Lancet. In it, he claimed that the MMR vaccine caused autism. It turned out that the paper was fraudulent and that Wakefield manipulated his research findings for financial gain. The Lancet retracted the paper and Wakefield lost his medical license.

“The Wakefield study was a total lie, but it made its way into the public eye,” Dr. Cuffman laments. It’s one of several misconceptions about the increasing prevalence of autism.

We’re probably still undercounting

Autism prevalence has been steadily increasing over the past few decades for many different reasons, like changes to the diagnostic criteria, increased public awareness of the condition and more equitable access to healthcare, testing and treatment. But that doesn’t mean the number we have today is necessarily accurate either.

The CDC determines autism prevalence by looking at the school and medical records of all the children living in a certain area. They then compare those numbers with data from other areas. Not only does that miss children who don’t have school or medical records, but it also doesn’t control for social determinants of health. For example, the raw data suggests that autism rates vary significantly by state, which doesn’t make sense. What those numbers actually reveal is the fact that some states are undercounting (and underserving) their autistic population.

That suggests autism prevalence is probably higher than the 1 in 36 statistic we’re working from right now.

As awareness continues to rise — and healthcare and support services become more accessible — we can expect the numbers to continue trending upward. And that’s a good thing because it means more people are getting the care they deserve.