As a growing number of Americans are being diagnosed with the coronavirus, doctors are learning more about who may be most susceptible to the most severe complications of the disease.

It's not just the elderly, already known to be at greater risk for this and other viral illnesses.

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New data from the Centers for Disease Control and Prevention echo what doctors on the front lines of treating the coronavirus have been reporting anecdotally: Younger adults who become infected aren't just getting mild illnesses. Many in their 20s, 30s and 40s are sick enough from the coronavirus to be hospitalized and need intensive care.

The CDC analyzed reports of 4,226 patients in the U.S. with confirmed COVID-19, the illness that results from the coronavirus infection, between mid-February and mid-March. Of those, 508 were known to be hospitalized.

While it's true that the oldest patients were most likely to end up in the hospital or die from the infection, more than half of the hospitalized patients in the study were under 65.

And 20 percent of those patients were in their 20s, 30s or early 40s. It's a big reason one of the most knowledgeable and respected members of the federal health coronavirus response is now focusing prevention messaging on younger generations.

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One influential podcaster, whose sports entertainment program, Barstool Sports' Pardon My Take, is popular with the under-30 crowd, told NBC News he was "a little bit freaked out" when Dr. Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases, approached him to do an interview.

"If the person who's in charge of the coordinated response to this disease is reaching out to our sports podcast, trying to reach millennials, things might be getting pretty bad," Eric Sollenberger, one of the podcast's hosts, told NBC News.

The podcast stepped back from its usual sports commentary this week and spent more than 40 minutes speaking with Fauci, arguably the nation's most reputable authority on the coronavirus.

Sollenberger, 35, said that particular episode was well received by listeners, even though the podcast's hosts had been making jokes about the coronavirus previously.

"We weren't taking it seriously," Sollenberger said, "but when we saw what Dr. Fauci had been saying, it felt like it was important to have someone on our show that was actively contributing to combating a lot of misinformation out there."

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Though it's well documented now that adults of any age are indeed vulnerable to the most severe complications of the coronavirus, including the need for mechanical ventilation and a long stay in intensive care units, some doctors are noticing trends in those most at risk.