TRUMP: "Tremendous increases ... really a horrible thing to watch the tremendous amount of increase."
THE FACTS: About 1 in 68 school-aged children has autism or related disorders, a rate that has stayed about the same for two years, the Centers for Disease Control and Prevention reported in March.
That's far more than in 2000, when the CDC estimated that about 1 in 150 children had autism. That increase is explained in large part by more awareness of the developmental disorder and changes in practice that broadened the definition for an autism diagnosis.
Labeling also is an issue, as parents became more likely to seek out the increasing services for autism and related disorders that are available in schools and other settings. Still, the CDC says that a true increase in the number of people with autism cannot be ruled out.
WHY IT MATTERS: While Trump during one primary debate insisted he was "totally in favor of vaccines," he has subscribed in the past to theories unsupported by scientific evidence linking vaccines to autism. He tweeted in 2012: "Autism rates through the roof--why doesn't the Obama administration do something about doctor-inflicted autism. We lose nothing to try." In 2014: "If I were President I would push for proper vaccinations but would not allow one time massive shots that a small child cannot take - AUTISM."
A similar assertion in a 2015 presidential primary debate brought a rebuke from the American Academy of Pediatrics, which said it is "dangerous to public health" to suggest that vaccines are linked to autism.
Although Trump has not made such categorical statements about vaccines and autism as president, he met during the transition with Robert F. Kennedy Jr., a prominent critic of an ingredient sometimes used in vaccines. Trump spokeswoman Hope Hicks said at the time that Trump was considering a panel on the subject.
More broadly, those who attribute autism to vaccination seize upon any rising numbers as an argument against vaccination. That has proven worrisome to public health officials because it could divert money away from things that should be a higher priority.
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Associated Press writer Jim Drinkard contributed to this report.