Autism rates have been increasing in the United States since epidemiologists and researchers first began tracking diagnostic rates in 2000.

There have been concerns that there is an “epidemic” of autism (concerns usually based on misunderstanding and misinformation). But the increase in the rate of positive diagnoses for autism is largely due to a better understanding of what autism and neurodiversity are and diagnostic criteria responding to this broader understanding. 

To understand how we know more than we did before, it is necessary to look at how clinicians diagnose autism.

How Autism Is Diagnosed

Doctors have to rely on observation and interaction with a patient before they can diagnose autism spectrum disorder. The criteria to guide these interactions comes from the Diagnostic and Statistical Manual of Mental Disorders. They specify that delayed or nonexistent norms in social communication and interaction, as well as limited interests and repetitive behaviors, are the core hallmarks of autism. 

The current rate of autism in the United States is 1 in 44 children with boys being four times more likely to be diagnosed with autism than girls. The disproportionate ratio between boys and girls led to calls to reevaluate how children are screened for autism, especially to address gender disparities in health care. This information contributed to changes in how autism diagnoses and rates are evaluated. 

The 1 in 44 rate comes from the Centers for Disease Control and Prevention (CDC) collecting health records from schools in certain counties. Every other year, trained clinicians check for any reports of social problems or repetitive behaviors that would raise the possibility of autism. Based on demographics, the numbers are then extrapolated to cover the entire state of those counties.

Increasing & Disparate Autism Rates

Since this method has been in use since 2000, it has changed the rate at which pediatricians and specialists diagnose autism, and rates have continued to rise.

When records first started being examined two decades ago, the rate was 1 in 150. Researchers discovered that the upward trend is found not just in the United States but all over the world. 

Even though this is now the accepted method of measuring the increase in autism diagnoses, scientists point out that the best way remains in-person evaluations and observations. Additionally, children who are homeschooled or who live in isolated areas with unreliable record-keeping may go unreported and undiagnosed.

An example of this is that autism rates are very different from state to state. Colorado has an autism diagnosis rate of 1 in 93 children, but New Jersey’s is 1 in 41 (the highest in the country, according to local media). Epidemiologists say it is unlikely that that degree of variation is due to natural causes. Instead, it is more likely that there are different levels of autism awareness and of available services in those states. 

Understanding Autism

The increase in autism rates in the United States is not only due to statistical factors. It is also due to how we understand autism spectrum disorder itself. From the time the diagnosis for autism was first introduced in 1943, the very definition of the disorder has been evolving, and this has influenced the changing rates of autism diagnoses.

For instance, researchers in 1966 estimated that only 1 in 2,500 children had autism because the more subtle presentations of the disorder were completely unknown, and doctors only focused on children who had more severe presentations of the spectrum. In fact, the thought of autism being on a spectrum was not posited until decades later.

In 1987, the new edition of the Diagnostic and Statistical Manual of Mental Disorders expanded the criteria of autism by requiring that a child needs to meet 8 of the 16 criteria instead of the 6 out of 6 that the previous edition of the DSM stipulated. These changes led to the rate of autism diagnoses increasing to 1 in 1,400. The rate has been increasing ever since. 

Special Education & Reclassification

Another milestone came in 1991 when the Department of Education granted special education services to children with autism. This might have encouraged families to seek out more help for their children if they felt that access to special education services, which they previously would not have been eligible to receive, was a possibility.

In the fourth edition of the DSM, published in 1994, the inclusion of Asperger syndrome (AS) as a milder form of autism spectrum disorder pushed the boundaries of the understanding of autism even further. Statistical findings from the CDC are based on the DSM-IV definition of autism. The DSM-5 edition condensed autism, AS, and pervasive developmental disorder — not otherwise specified — into a single diagnosis. This reclassification was met with controversy by autism advocates, while it was supported by some researchers.

However, the DSM-5 did address the concern of autism spectrum disorder and attention deficit hyperactivity disorder being diagnosed together, as was the case in past editions. This may have led to some people with autism being misdiagnosed with attention deficit hyperactivity disorder (ADHD).

The DSM-5 allows for diagnoses of more than one disorder. Many children who have developmental delays are now regularly screened for autism. This increases the possibility that they may be correctly diagnosed and drives up the rate of autism diagnoses in the United States.

In 2006, the American Academy of Pediatrics recommended that all children ages 18 to 24 months be screened for autism during their routine pediatrician visits. It is possible that this suggestion led to many diagnoses of autism in children that may otherwise never have happened. 

Demographics & Diagnoses

Specialists and researchers believe that the driving factor behind the increase in autism rates in the United States has been that there is much more awareness of the disorder than there was a generation, or even a decade, ago. As recently as the 1970s, many people who had autism, diagnosed or undiagnosed, were committed to institutions, effectively removing them from any form of help and removing them from any statistics about autism.

Further to that point, parents who know about autism are much more likely to ask for help than parents who are unaware of the symptoms. People who live in urban areas (or close to them) and who have access to health care and education are more likely to be informed about autism enough to consult a doctor for help or assistance. This may also contribute to the reason diagnostic rates have increased.

This also means that school nurses and teachers are more likely to recognize the characteristic signs of autism — such as limited interests, repetitive behaviors, and communication and social challenges — and accurately document these in school and medical records.

One particular population that is key to the increase of autism rates in the United States is the female demographic. For a generation, it was assumed that girls could not “get” autism, primarily because girls were socialized to be less outspoken and less active than boys. Girls who had autism were thought to be acting in accordance with the gender norms of the time. 

Systemic Underrepresentation in Autism Rates

Access to health care reduces the rate of systemic misdiagnoses in minority ethnic populations. Historically, Hispanic and African American children have had lower rates of autism diagnoses because their communities have had more limited access to health care. There has also been more limited access to education about autism, which has further contributed to disproportionately lower rates.

As a result of these problems, autism diagnoses were traditionally higher in white children in America, leading to “wide underrepresentation” of autism in minority groups. Increased education and health care access for minority communities have improved the detection of the disorder.

This has contributed to the prevalence of autism diagnoses across different American demographics and socioeconomic statuses. To that point, the PLOS One journal noted in 2015 that the prevalence of autism “is more likely to be higher in areas with the highest level of [socioeconomic] deprivation.”

Autism Rates Across the World

This is not just the case in the United States but also around the world.

Reporting on the Lancet’s Global Burden of Disease study, Axios wrote in 2018 that 4.57 million children under the age of 5 have autism, or 1 in 138 children in every country. Most of them live in developing or low-income countries: 1 million in the Sub-Saharan African and South Asian regions. The highest rates of childhood autism are in the Middle East, North Africa, and Central Asia. 

So much of the dialogue around autism looks at developed countries, like the United States, Canada, and Western Europe, that it tends to be overlooked that the rate of childhood autism is concentrated primarily in areas where access to health care and education are limited. The actual number and rate of autism diagnoses across the world is likely far higher than what it is now.

From a global perspective, there are 851,000 children with autism in India, by far the largest in the world. The next highest is China, with 422,000. Between the United States and Canada, there are about 150,000 children with autism and 140,000 across Western Europe. 

Contributing Factors

Does this mean that there is no actual increase in the rate of autism in the United States? As much as we know more about the disorder, and criteria have changed to accommodate this increased understanding, there are also potential biological factors that contribute to the increase.

Researchers know, for example, that children born to older parents (and in particular, older fathers) have a higher risk of developing autism than children born to younger parents. Similarly, children born prematurely may have a higher likelihood of being born on the spectrum. But advancements in medicine have ensured that children born prematurely have a much higher survival rate than ever before. This, unintentionally, might contribute to the increased rate of autism in children in the United States