Record-Breaking Autism Rates Reported With New CDC Criteria

Kelli Whitlock Burton

December 02, 2021

Childhood autism rates are at the highest level since the Centers for Disease Control and Prevention (CDC) began tracking the disorder in 2000, new data released today show.

The increase likely reflects improvements in diagnosis and identification of autism spectrum disorder (ASD), not an increase in incidence, study authors with the CDC's Autism and Developmental Disabilities Monitoring (ADDM) Network told Medscape Medical News.

Using a new surveillance methodology, researchers found that 2.3% of 8-year-olds in communities in 11 states across the US had an autism diagnosis in 2018, up from 1.9% in 2016.

A separate report on early identification in 4-year-olds shows that children born in 2014 were 50% more likely to receive an autism diagnosis or ASD special education classification by 48 months of age than those born in 2010, signaling improved early diagnosis.

Taken together, the data suggest efforts to raise awareness about autism are working, though researchers were quick to say much work remains.

"It was not surprising to me and in fact it was reassuring that the number of children diagnosed with autism is higher and is actually approaching prevalence of autism that has been noted in some national surveys of parents," Stuart Shapira, MD, PhD, associate director for science in CDC's National Center on Birth Defects and Developmental Disability, told Medscape Medical News.

"It means we're doing a better job of identifying children, which helps to get them into services earlier so they can achieve their best developmental outcome."

The studies, published online December 2 in Morbidity and Mortality Weekly Report, are the first to use a new ASD surveillance protocol that relies on ASD diagnosis or special education classification and billing codes and eliminates comprehensive records analysis by trained clinician reviewers.

Racial Disparities

The updated methodology was less labor-intensive and reduced the time it took to produce the report, but it is not without its critics, who claim the new protocol will undercount the number of children with ASD.

Created in 2000 and funded by the CDC, the ADDM Network is the only surveillance program in the US that tracks the number and characteristics of children with ASD in multiple communities in the US.

When ADDM released its first report in 2007 from six states and based on data from the year 2000, ASD prevalence was 6.7 per 1000 children, or 1 in 150 children.

In the latest report, which includes data from 2018, the autism prevalence rate across 11 states was 23.0 per 1000 children, or 1 in 44 children.

That rate is closer to reported autism prevalence from the National Survey of Children's Health and the National Health Interview Survey, both of which rely on parent-reported ASD diagnoses.

For the report, researchers analyzed medical and special education records of 220,281 children who were born in 2010 in Arizona, Arkansas, California, Georgia, Maryland, Minnesota, Missouri, New Jersey, Tennessee, Utah, and Wisconsin.

Children were counted as having autism if their records included an ASD diagnosis, a special education classification of ASD, or an ASD International Classification of Diseases (ICD) code. A total of 5058 children met those criteria.

Rates of ASD ranged from a low of 1.7% in Missouri to 3.9% in California and were 4.2 times higher in boys than in girls. Just under half of the children with ASD were evaluated by age 36 months.

Although the overall ASD prevalence was similar among White, Black, Hispanic, and Asian/Pacific Islander children, the report highlighted a number of other racial disparities overall and in individual states.

For example, among those with ASD and data on cognitive ability, 35.2% had an intelligence quotient (IQ) score of ≤70. Black children with ASD were far more likely to have an IQ of ≤70 (49.8%) than Hispanic (33.1%) or White (29.7%) children.

Dr Matthew Maenner

"The persistent disparities in co-occurring intellectual disabilities in children with autism is something that we continue to see and suggests that we need to better understand exactly what's happening," Matthew Maenner, PhD, an epidemiologist and autism surveillance team lead with the CDC's National Center on Birth Defects and Developmental Disabilities, told Medscape Medical News.

Another long-standing trend observed again in the new report on prevalence among 8-year-olds is low ASD prevalence among Hispanic children. While the overall estimate showed similar autism rates, a closer review of state-level data reveals a different picture.

"In almost half of the sites, Hispanic children were less likely to be identified as having ASD," he said. "This gets lost if you look only at the overall estimate."

New Methodology

When ADDM released its first report in 2007, autism diagnosis was widely inadequate in the US. Relying only on confirmed ASD diagnoses would significantly underestimate the number of children with the disorder, so the CDC added "active case finding" to the protocol.

Trained clinician reviewers analyzed individual notes from medical and educational records for every 8-year-old in ADDM Network sites, looking for evidence of characteristics and behaviors associated with autism. The process was labor- and time-intensive and took up to 4 years to complete.

In 2018, the CDC began investigating ways to speed the process and came up with the strategy used in the latest report. The new protocol was faster, easier, and less expensive. Although he says cost was never the deciding factor, Maenner acknowledges that had they stuck with the original protocol, they would have been forced to reduce the number of ADDM Network sites.

Maenner argues that a comparison of the two protocols shows the new method doesn't compromise accuracy and may actually capture children who lacked the medical or educational records the previous protocol required for a count. But not everyone agrees.

Dr Walter Zahorodny

"I thought the point was to be as accurate and complete as possible in doing the surveillance," Walter Zahorodny, PhD, associate professor of pediatrics at Rutgers University and principal investigator of the New Jersey ADDM Network site, told Medscape Medical News. "In states where there's a high detail of information in records, like New Jersey, it's going to underestimate the count."

Zahorodny says the latest data prove his point. In 2016, under the old methodology, ASD prevalence was 3.1% in the state. In 2018, under the new protocol, prevalence was 2.84%, a decrease of about 20% that Zahorodny pins squarely on the elimination of ADDM clinical reviewers.

But New Jersey is the only state that participated in both the 2016 and 2018 surveillance periods to report a decrease in ASD prevalence. The other eight states all found autism rates in their states went up.

Sydney Pettygrove, PhD, associate professor of public health and pediatrics at the University of Arizona and a principal investigator for the ADDM site in Arizona, told Medscape Medical News that when she first learned the CDC was rolling out a new methodology, she and other investigators were concerned.

"People were really upset. I was really upset," she said. "I had formed an opinion based on the earlier data that this would not be a good idea."

In 2000, when ASD surveillance began in Arizona, nearly 30% of children identified by ADDM clinical reviewers as having autism had no mention of the disorder in their records. Today, that percentage is closer to 5%.

"In 2000 it would have been catastrophic to try to estimate the prevalence of autism with the new protocol," said Pettygrove. As it turns out, under the new protocol, prevalence rates in Arizona increased from 16.0 per 1000 children in 2016 to 24.9 in 2018.

Built-in Bias Eliminated?

In addition to speeding up the process, the new methodology might have other benefits as well. Under the old ADDM surveillance protocol, children who lacked certain medical or educational records did not meet the ASD case definition and weren't counted.

A 2019 study showed that this disproportionately affected Black and Hispanic children, who had significantly less access to healthcare professionals than White children.

As a result, "the old methodology had a bias built into it," Maureen Durkin, PhD, DrPH, co-author of that study and chair of population health sciences at the University of Wisconsin-Madison and principal investigator for the ADDM site in Wisconsin, told Medscape Medical News.

"Clinician reviewers ended up putting these children in the 'suspected ASD' category because they couldn't call it a case under the case definition," Durkin said. "There was a fairly large percentage of suspected cases and a disproportionate number of those kids were children of color."

Although she can't say for sure, Durkin said it's possible the new protocol could eliminate some of that bias.

CDC researchers also attribute the new method to an expanded study of early diagnosis among 4-year-olds. In previous years, only a handful of the ADDM Network sites participating in the 8-year-old surveillance project also studied early diagnosis in 4-year-olds.

This year, all 11 sites took part in the early diagnosis analysis, tripling the number of children included in the analysis. That made it possible to include, for the first time, Asian/Pacific Islander children in this analysis.

In the past, ASD prevalence has trended higher in White children compared to other racial groups. The new data found that ASD prevalence among 4-year-olds was significantly lower in White children (12.9 per 1000 children) than in Black, Hispanic, or Asian/Pacific Islander children (16.6, 21.1, and 22.7 per 1000, respectively). Prevalence in American Indian/Alaska Native children was the lowest among all racial groups (11.5 per 1000).

It's the first time researchers have seen this pattern in any ADDM report, Kelly Shaw, PhD, lead author of that study and an epidemiologist with the National Center on Birth Defects and Developmental Disability at the CDC, told Medscape Medical News.

These data don't provide clues about the potential cause of that disparity, Shaw said. It's likely an indication of better identification of ASD in those communities, she said, and not a sign of increased incidence of autism among Black, Hispanic, or Asian/Pacific Islander children.

"We don't have any evidence to suggest or expect that autism would be increasing differentially among groups," Shaw said.

The data suggest "we are making some progress but there certainly is still room for improvement," Shaw said.

Study authors report no conflicts of interest.

MMWR Morb Mortal Wkly Rep. Published online December 2, 2021. Full text

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