As many as 1 in 4 teens with autism may be undiagnosed, new research suggests.
"Autism is much more prevalent than people assume,"said lead researcher Walter Zahorodny, an associate professor at Rutgers New Jersey Medical School in Newark.
The new study is significant, he said, because it's the first population-based public health look at the prevalence of autism in teens.
For the study, his team reviewed school and health records of close to 4,900 16-year-olds living in four northern New Jersey counties in 2014. The initial review found 1,365 cases that merited a closer look.
Of those, a diagnosis of autism spectrum disorder (ASD) was confirmed in 560, according to the study.
From the chosen cases, 384 had been diagnosed at age 8, and 176 met the diagnostic criteria for autism at 16.
Put another way, 1 in 55 kids in the four New Jersey counties had autism, but one-quarter were undiagnosed until this study took place.
Of those with autism, 3 in 5 also had another neuropsychiatric disorder, most often attention-deficit/hyperactivity disorder (ADHD), the study found.
While this study focused only on one part of New Jersey, Zahorodny said the findings would likely be similar in other regions.
"I'm certain if we were to look carefully in California, Midwest, every part of the United States, we would find high rates of autism, not only among children, but adolescents as well,"he said.
The U.S. Centers for Disease Control and Prevention notes that the number of kids with autism varies considerably from state to state.
Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at the Cohen Children's Medical Center of New York, reviewed the findings. He said the numbers may be even higher now.
"New Jersey has always been recognized as being good about identifying and providing services for children and adolescents with ASD,"he said. "And if you look at the prevalence of ASD in New Jersey versus other parts of the country for whatever reason -- and we don't fully understand the reasons -- it's as much as twice as high."
Adesman noted that the prevalence of autism has increased considerably since 2014, the year researchers used in their study.
"So the numbers that are cited here may be an underestimate of the number of individuals with ASD and adolescents presently,"he said.
Rates of autism also vary across gender, ethnicity and economic status, this and other studies have found.
One in 55 boys and 1 in 172 girls in the cohort were identified with ASD, and autism was found to be twice as common in teens from higher-income households compared to low-income ones.
Autism was also more prevalent in white teens compared to Black teens and Hispanic teens. There weren't enough Asian teens in the group to compare rates.
However, a nationwide study published in March found that autism rates rose from 1 in 44 in 2018 to 1 in 36 in 2020, with autism being diagnosed more frequently for the first time among Black children and Hispanic children than white children. The authors attributed this to improved screening and autism services for all kids.
Zahorodny said he and his colleagues plan to continue their study of this group.
"Our next hope would be to see if we could follow up with this cohort of individuals because we can still learn a lot,"he said. "There's very little, in fact, known about the expression of autism and young adults and to follow up with this cohort would be ideal because we could be tracking the changes in autism over time and thereby also reflecting what kind of care or intervention might be suited for affected individuals."
The findings were recently published online in the Journal of Autism and Developmental Disorders.
More information
For more on autism, visit the U.S. National Institute of Mental Health.
SOURCES: Walter Zahorodny, PhD, associate professor-research, department of pediatrics, and director, NJ Autism Study, Rutgers New Jersey Medical School, Newark; Andrew Robert Adesman, MD, professor, Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, Uniondale, N.Y., and chief, developmental and behavioral pediatrics, Cohen Children's Medical Center of New York, New Hyde Park, N.Y.; Journal of Autism and Developmental Disorders, Aug. 29, 2023
