The number of autism diagnoses in the United States has been steadily increasing since the year 2000, when researchers first started monitoring it. This rise has led to concerns about an autism ‘epidemic.’ However, experts suggest that this increase is largely due to greater autism awareness and changes in how the condition is diagnosed.
Here’s a look at how researchers track autism prevalence and the reasons behind its apparent increase over time.
How is Autism Diagnosed by Clinicians?
Currently, there is no objective medical test like a blood test or brain scan to diagnose autism. Researchers are actively working on developing such tests, but for now, clinicians rely on observing an individual’s behavior to make a diagnosis.
In the United States, the “Diagnostic and Statistical Manual of Mental Disorders” (DSM) provides the criteria for diagnosing autism. These criteria include challenges in social communication and interaction, along with restricted interests or repetitive behaviors. Crucially, these core features must be evident in early childhood development.
What is the Current Prevalence of Autism in the U.S.?
The Centers for Disease Control and Prevention (CDC) estimates that approximately 1 in 68 children in the U.S. are diagnosed with autism spectrum disorder. Breaking this down by gender, prevalence is about 1 in 42 for boys and 1 in 189 for girls. This results in a gender ratio of roughly five boys diagnosed with autism for every girl.
How Does the CDC Determine Autism Prevalence Rates?
CDC researchers gather health and school records of 8-year-old children living in selected counties across the U.S. This data collection is part of the Autism and Developmental Disabilities Monitoring (ADDM) Network, established by the CDC in 2000 to track autism prevalence.
Every two years, trained clinicians review these records for indicators of autism, such as difficulties with social interaction or repetitive behaviors. They concentrate on 8-year-olds because, by this age, most children are enrolled in school and have undergone regular health check-ups, increasing the likelihood of these features being documented. Based on their record reviews, clinicians determine if a child meets the diagnostic criteria for autism, even if they haven’t received a formal diagnosis. These findings are then used to estimate autism prevalence across broader populations.
The latest prevalence estimates are based on data collected from 11 ADDM Network sites in 11 different states. For future assessments, the CDC plans to focus on 10 of these sites. In six of these locations, clinicians intend to examine records of children at both 4 and 8 years old to gain a more detailed understanding of Autism Diagnosis Over Time.
The Trend of Autism Prevalence Over Time
The most recent prevalence estimate of 1 in 68 represents a 30 percent increase from the 2008 rate of 1 in 88, and more than double the 2000 rate of 1 in 150. According to Maureen Durkin, who leads the ADDM Network site in Wisconsin, the trend of rising autism prevalence has been consistently upward since the early 1990s, not just in the U.S. but worldwide.
Accuracy of the CDC’s Prevalence Tracking Method
According to Eric Fombonne, a psychiatry professor at Oregon Health and Science University in Portland, the strength of the CDC’s method is that it captures a broad view of all children within a specific area, not just those who have been formally diagnosed. However, he points out that relying on school and medical records is less precise than direct, in-person assessments of children.
This method may also miss children who lack school or medical records, such as those who are homeschooled or live in remote areas. Furthermore, the children within the monitored areas may not fully represent all children within a given state.
The variability in autism rates across different states is one indication of the method’s limitations. For example, Colorado has a prevalence of 1 in 93 children, while New Jersey’s rate is 1 in 41. Fombonne suggests that these significant state-to-state differences are unlikely to be naturally occurring variations. Instead, they likely reflect differences in autism awareness levels and the availability of support services in those states, impacting autism diagnosis over time.
Evolution of Autism Definition and Diagnostic Criteria Over Time
Our understanding and diagnosis of autism have changed considerably since the condition was first identified nearly 75 years ago. In 1943, Leo Kanner first used the term ‘infantile autism’ to describe children who appeared socially detached and withdrawn.
In 1966, based on Kanner’s descriptions, researchers estimated autism prevalence to be about 1 in 2,500 children. These early estimates likely focused on individuals with more severe presentations of autism, missing those with milder characteristics.
Autism was not officially included in the DSM until 1980. In 1987, a revised DSM expanded the diagnostic criteria, allowing for diagnosis even if symptoms became apparent after 30 months of age. The number of criteria needed for diagnosis was also changed; a child needed to meet 8 out of 16 criteria, compared to all 6 in the previous version. These changes may have contributed to an increase in prevalence, slightly exceeding 1 in 1,400.
In 1991, a significant policy change occurred when the U.S. Department of Education ruled that an autism diagnosis qualified a child for special education services. Before this, many children with autism might have been categorized as having intellectual disabilities instead. This policy shift may have encouraged families to seek an autism diagnosis for their children, influencing autism diagnosis rates over time. It’s also important to note that the number of children diagnosed with both autism and intellectual disability has also been on the rise.
The 1994 DSM-IV further broadened the autism definition by including Asperger syndrome, representing the milder end of the autism spectrum. The current DSM-5, released in 2013, consolidated autism, Asperger syndrome, and pervasive developmental disorder-not otherwise specified into a single overarching diagnosis of autism spectrum disorder.
The most recent CDC prevalence estimates are based on the DSM-IV criteria. Future estimates will utilize DSM-5 criteria, which some experts predict may potentially lead to a decrease in reported autism rates, reflecting the ongoing evolution of autism diagnosis over time.
The Role of Increased Autism Awareness in Rising Prevalence
Increased awareness of autism is undoubtedly a significant factor contributing to the rise in prevalence, according to Durkin.
Prior to the 1980s, many individuals with autism were institutionalized, making them largely invisible to the broader society. Studies indicate that parents who are familiar with the characteristics of autism—perhaps through knowing someone with the condition—are more likely to seek a diagnosis for their children compared to parents without such awareness. Living in urban areas and having better access to healthcare also increase the likelihood of receiving a diagnosis, reflecting societal factors influencing autism diagnosis over time.
Greater autism awareness also likely inflates CDC prevalence estimates by increasing the chances that autism-related traits, like limited eye contact, are noted in school and medical records, as Fombonne suggests.
Policy changes, such as the 2006 recommendation by the American Academy of Pediatrics to screen all children for autism during routine pediatrician visits at 18 and 24 months, have also played a role. This proactive screening may have identified children who might have otherwise gone undiagnosed, further impacting autism diagnosis rates over time.
Other Influencing Factors on Autism Prevalence
In the past, some individuals now diagnosed with autism might have been misdiagnosed with intellectual disability or other conditions. Interestingly, as autism diagnoses have increased, diagnoses of intellectual disability have shown a decrease, suggesting a diagnostic shift over time.
Furthermore, an autism diagnosis often provides greater access to specialized services and special education compared to other diagnoses. This can make clinicians more inclined to diagnose autism, even in cases where a child may be on the borderline of the diagnostic criteria, reflecting the influence of service availability on autism diagnosis over time.
Previous versions of the DSM did not allow for co-diagnosis of autism and attention deficit hyperactivity disorder (ADHD). The DSM-5 now permits multiple diagnoses, and children with developmental delays are commonly screened for autism as part of routine assessments.
Historically, autism prevalence has been highest among white children in the U.S. However, this is beginning to change. African-American and Hispanic children have previously had lower diagnosis rates, often due to disparities in access to healthcare and diagnostic services. Widespread screening efforts are improving the detection of autism in these groups, contributing to a rise in overall prevalence rates and addressing historical inequities in autism diagnosis over time.
Is There a Genuine Increase in Autism Rates, Beyond Diagnostic Changes?
While increased awareness and evolving diagnostic criteria are likely responsible for a significant portion of the rise in prevalence, biological factors may also play a role, according to Durkin. For instance, having older parents, particularly an older father, has been linked to a slightly increased risk of autism. Additionally, premature birth is also associated with a higher risk of autism, and advancements in medical care mean that more premature infants are surviving today than in the past. These biological and demographic shifts may also be contributing factors to the observed changes in autism diagnosis over time.
This article is reproduced with permission from Spectrum. The article was first published on March 2, 2017.
