Health and Human Services Secretary Robert F. Kennedy Jr. had said that he expected to have answers by the fall on why the number of autism diagnoses has increased in recent years.

But it appears Kennedy will have to wait a little longer.

National Institutes of Health Director Dr. Jay Bhattacharya told CBS News that "we want to get moving on this as rapidly as we can." But he suggested it will take longer for research to be completed.

"We're going to get hopefully grants out the door by the end of the summer," Bhattacharya said. "And people will get to work. We'll have a major conference, with updates, within the next year."

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CBS News also reported that Bhattacharya did not misspeak, but that he was "enthusiastic to get the scientific process going."

The number of autism diagnoses in the U.S. has increased in recent years, as confirmed by a new Centers for Disease Control and Prevention report that found that 1 in 31 children born in 2014 were diagnosed with autism spectrum disorder. A previous CDC report indicated that among children born in 2012, 1 out of 36 had been identified with autism spectrum disorder by the time they turned 8 years old. Among children born in 1992, that proportion was 1 in 150, according to the Centers for Disease Control and Prevention.

No one knows why autism rates have spiked in the past 25 years, but scientists think much of it is due to a broader definition of the disorder and better detection. They also say genetics and exposure to chemicals may play a role. "We're seeing the rates of autism go up because we're doing a better job of understanding what autism is," Dr. Jessica McCarthy, a licensed clinical psychologist, told Scripps News earlier this month. "We're doing a better job of assessing it and diagnosing it in greater areas around the country, both in terms of targeted areas of the country and also in populations that we know are chronically underserved in healthcare."

Kennedy, however, disputed the CDC report's conclusions that enhanced screenings are behind the increase. "One of the things that I think we need to move away from today is this ideology that the autism diagnosis, that the autism prevalence increases, the relentless increases, are simply artifacts of better diagnosis, better recognition, or changing diagnostic criteria," he said.

Bhattacharya told CBS that Kennedy would not be directly involved in the research. "Secretary Kennedy has not ever, in my experience, put his thumb on the scale in that way. And nor do I intend to do that," Bhattacharya said.

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