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  • Writer's pictureJen Ottolino

One Epidemiologist's Take on the Increasing Prevalence of Autism Spectrum Disorders in the US

Updated: Apr 25, 2023

The CDC has been tracking autism spectrum disorders for several decades, and the numbers keep increasing. Does this mean we are experiencing an autism epidemic?

Jen Ottolino (me) and Sydney Pettygrove during a random and unexpected airport encounter

Back in the early 2000s, I helped set up one of the original sites in the Autism and Developmental Disabilities Monitoring Network (ADDM), a group of communities working with the CDC to monitor the prevalence of autism spectrum disorders (ASDs) in 8-year-old children in the US. Working with other public health professionals in this important endeavor—the first national effort to assess the prevalence of ASDs—was one of the most rewarding experiences of my career.

The CDC's Latest ASD Prevalence Report

I have been following the network’s surveillance efforts since I left the project, and a few weeks ago, the CDC published the network’s latest prevalence estimates in the Morbidity and Mortality Weekly Report. The report indicated that in 2020, 1 in 36 8-year-old children in these communities (2.8%) were identified as having ASDs.

Over the years, the network’s prevalence estimates have been steadily increasing, with the most recent estimate higher than that in any other year. To some, these figures are alarming. Do they confirm we are facing an autism epidemic?

Interview with Epidemiologist Sydney Pettygrove, PhD

Last week, I chatted with Sydney Pettygrove, my former boss at the Arizona ADDM site. Sydney is a professor in the Epidemiology and Biostatistics Department at the University of Arizona and has been a principal investigator in the CDC's developmental disabilities surveillance network for over 20 years now. We talked about how the network got started, her role in it, the latest prevalence estimates, and what this work all means in the grand scheme of things.

Jen: Can you summarize why the CDC wanted to do this project?

Sydney: It had been thought that autism was rare. One in 1,000 was pretty much I think what was being estimated. Then some people in Brick Township, New Jersey contacted the CDC and said, “We are diagnosing kids with autism all over the place here. What is going on?” Their thinking was, “This is a rare condition, but we’re finding it everywhere we look.”

So, the CDC came in and did an evaluation. They had already established the Metro Atlanta Developmental Disability Surveillance Program (MADDSP), where they were doing surveillance for developmental issues like cerebral palsy, blindness, hearing impairment, vision, etc. When the CDC came to Brick Township, they employed the active surveillance methods that they were using in MADDSP, and they found a lot more autism than they would have expected based on the literature available at the time. Because of this, the CDC became interested in pursuing surveillance for autism. Then the parent community—parents of children with autism—rallied around and advocated in Congress for more funding for surveillance to at least figure out, how frequent is it?

Jen: Yes, I remember there were concerns that autism was becoming epidemic.

Sydney: Yes, the word epidemic was tossed around a lot: “We're having epidemic of autism.” So, Congress gave the CDC the money to do surveillance. The CDC then put out a request for proposals to universities and health departments. Here in Arizona, we applied and got funding.

Jen: What was your role with the project at that time?

Sydney: This was 2001, coming up on 22 years ago—the beginning of the network. Really, it was very exploratory and experimental for everyone figuring out how to make it work. As an epidemiologist, my degree was pretty new. I had not really done a whole lot yet. They brought me in to help get things up and running. A lot of what I did at the beginning was trying to work on those data sharing agreements, figuring out what to say to entice people to cooperate with us and allow us to look at their records.

Jen: What did you find that first year, after collecting and analyzing the first data set?

Sydney: Well, the prevalence we found by using active surveillance measures, which meant really going out and looking at medical and school records to find cases, was 6.7 per 1,000. That was the average across the sites, and it was significantly more cases of autism than we ever would have expected based on the previous literature, even based on the CDC's review in Brick Township.

Jen: What did you find in the next years of data collection?

Sydney: From 6.7, we went up and up. Then Arizona had a little plateau, like in 2012 and 14. We leveled off at around 9, I think. The other sites kept going up. Then in 2016, Arizona started to go up again, and it's continued to go up.

Jen: Now, the prevalence estimates are so much higher they were in the first years.

Sydney: It’s tempting to think that the estimated prevalence is going up because there are some more kids out there with autism. But that’s not what we think. It may be that there are more cases of autism to a certain extent, but we don't think that’s the full picture. I think awareness explains a lot more of the increase than anything: people waking up and realizing that autism spectrum disorders are common. We’re not having an outbreak. We're having an eye opening. It's like, oh, there’s a lot more neurodiversity than we had previously recognized.

Jen: Yes, it’s amazing how much more aware and informed people are about ASDs now than when I first started with the project.

Sydney: Because we’ve gone out and looked for ASDs and found them and then published the results, people have gotten more aware of the conditions as time has gone on. Now, there's nowhere I go to give a talk that I don't have someone—at least one person in the audience—come up and say, I have a brother, sister, cousin, friend, child that’s on the spectrum. People are talking about it more.

Jen: What’s the take home message of all of this, Sydney? What does this mean for us as a society, as a human family?

Sydney: In 2008, around the time of the unpleasantness in the economic markets, I was driving my son to middle school and he asked, “If there's a recession, why are all these people buying Mustangs?”

And I was like, “What?”

He said, “Look, there's a Mustang. There's a Mustang, there's a Mustang.”

I was like, “Really? I never noticed.”

Then we started playing a game to see who could point them out first.

Green Mustang! Yellow Mustang! Red Mustang! They're everywhere. I had no idea there were so many Mustangs driving around. Same with autism. Only when you start really looking in a systematic fashion do you really start to understand how frequent it is. We weren't looking before.

So that's the take home message of all of this: Wake up! Neurodiversity is all around us.

Jen: That’s a powerful take-home message. Thank you for your time, Sydney. And congratulations on your 20+ years of work on this important project.

To learn more about the CDC's most recent ASD prevalence estimates, read the full report in the MMWR.

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