(Reuters) – Rates of autism spectrum disorder among U.S. children reached a record level in 2022, continuing a recent trend of increasing prevalence, according to data released on Tuesday by the U.S. Centers for Disease Control and Prevention.

At 16 monitoring sites in 14 U.S. states and Puerto Rico, prevalence of the disorder among 8-year-olds in 2022 was 32.2 per 1,000, or 1 in every 31. That was up from 1 in 36 in 2020 and 1 in 44 in 2018, researchers reported in the CDC’s Morbidity and Mortality Weekly Report.

Autism Rates Change

Rates ranged from about 1 in 103 8-year-olds being diagnosed in one south Texas county, to about 1 of every 21 in a suburban county near Philadelphia and roughly 1 in 19 near San Diego, California.

Differences in prevalence over time and across sites can reflect differing practices in autism screening and diagnosis and availability of services, the researchers said.

“The true or actual rate of autism (in the United States) is more likely to be closer to what this report has identified in California or Pennsylvania,” said study co-author Walter Zahorodny of Rutgers University in New Jersey. “California in particular has a longstanding and excellent program for screening and early intervention.”

“The problem is there’s not a lot of research that gives us a strong indication for what is driving the rise,” Zahorodny said.

Rising rates of autism in the United States since 2000 have intensified public concern over what might be contributing to its prevalence. A large recent study added to evidence that diabetes during pregnancy is linked with an increased risk of brain and nervous system problems in children, including autism.

Robert F. Kennedy Jr., who now runs the U.S. Department of Health and Human Services and has long promoted a debunked link between vaccines and autism, last week set a September deadline for the U.S. National Institutes of Health to determine the cause behind the rise in autism rates.

CDC Study Not Designed to Identify Possible Cause in Rise of Autism

The populations at the 16 monitoring sites do not precisely reflect the characteristics of the entire country, and the CDC study was not designed to identify possible causes of any increase in prevalence.

Considering the wide variations in autism symptoms among individuals, a combination of genetic and environmental factors that together affect early brain development are likely to be the cause, said Dr. Lang Chen of Santa Clara University in California, who studies the brain networks involved in learning disabilities and autism but was not involved in the CDC study.

“However, it is critical to know that there is no scientific evidence supporting the link between vaccines and autism,” he said.

Zahorodny noted that vaccination rates have been falling while autism diagnoses have risen.

As in 2020, ASD prevalence among 8-year-olds was higher among Asian/Pacific Islander, Black, and Hispanic children than among white children, the CDC data showed.

Asian/Pacific Islander, Black, and Hispanic children with ASD were more likely than white or multiracial children with ASD to also have an intellectual disability.

The data also showed that ASD is more common among boys than girls.

The disorder is increasingly being identified at younger ages, with higher rates of diagnosis by age 4 among children born in 2018 compared with those born four years earlier.

Heightened awareness and the inclusion of a wider range of behaviors to describe the condition have contributed to the increase but do not explain all of it, experts say.

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(Reporting by Nancy Lapid; additional reporting by Joshua Schneyer; Editing by Bill Berkrot)