The number of American children and adults diagnosed with autism increased 175% in roughly a decade, according to new research that shows an uptick among certain groups appears to be driving the trend.

In a review of electronic health records and insurance claims data for about 12 million people between 2011 and 2022, researchers found the odds of an autism diagnosis “increased substantially.”

The study published this week in the journal JAMA Network Open indicates that autism prevalence jumped from 2.3 per 1,000 to 6.3 per 1,000 during the period studied.

The biggest change was seen in adults ages 26 to 34, a group that saw a 450% increase in autism diagnoses, the study found. There was also significant growth in diagnoses of female versus male children.

The highest prevalence of autism was seen among children ages 5 to 8, the study found. Kids from racial and ethnic minority groups saw bigger increases than white children, though that trend did not hold in adults.

For the study, researchers at Kaiser Permanente analyzed records for patients at eight health care systems that are part of a consortium of research centers known as the Mental Health Research Network. Individuals were determined to be on the spectrum if they had an autism diagnosis under the ninth or tenth revisions of the International Classification of Diseases, a standardized system used to code medical conditions.

“The improvement and expansion of universal developmental screening likely accounts for some of the increase in diagnosis rates we found in this study,” said Luke Grosvenor, the study’s lead author and a research fellow at the Kaiser Permanente Division of Research. “The magnitude of the rate increases and variability by age, gender, race and ethnicity suggests factors other than improved screening are also contributing to the rate increases.”

The study stands out for looking at autism rates among people of all ages, as most prevalence research focuses on kids. However, the findings are largely consistent with data collected through the Centers for Disease Control and Prevention’s Autism and Developmental Disabilities Monitoring Network, which tracks autism rates in children, the researchers said.

The population of adults with autism is expected to keep growing, with a “substantial number of autistic people aging into adult care,” the study concluded, highlighting the need for greater health care services for this group.