For the first time ever, researchers at the Centers for Disease Control and Prevention are estimating the number of American adults who have autism.

More than 5.4 million people in the U.S. — or 1 in 45 — over age 18 are on the spectrum, according to findings published online this week in the Journal of Autism and Developmental Disorders.

CDC researchers looked at autism prevalence rates for kids reported through the National Survey of Children’s Health — an annual government survey that asks parents across the nation if they’ve ever been told by a health care provider that their child has autism — between 2016 and 2018. Then, they estimated adult prevalence by adjusting the children’s numbers to account for mortality as people age and cross-referenced the figures with Census data on the population of each state.

Overall, the study found that 2.21 percent of adults across the country have autism. Prevalence varies by state, with a high of 2.42 percent in Massachusetts and a low of 1.97 percent in Louisiana.

The states with the largest populations of adults on the spectrum include California with more than 700,000, Texas at nearly 450,000, New York with over 340,000 and almost 330,000 in Florida, according to the findings.

Like in children, the study found that autism is far more common in men compared to women, with females accounting for just over a million of the adults estimated to the have the developmental disorder.

Matt Maenner, an epidemiologist at the CDC’s National Center on Birth Defects and Developmental Disabilities who worked on the research, described the study as an effort to fill an “enormous data gap.” The CDC has multiple methods to track the number of children with autism, but has no surveillance system in place to measure prevalence in adults.

“For us, putting this estimate out there … it’s a starting point,” said Maenner who indicated that the research on adults is part of a broader CDC effort to assess autism in a wider range of ages. “One of the things that strikes me is that 5 million people is a lot of people and that can be useful in anticipating not only future needs, but understanding what are the needs today.”