Federal officials announced Friday they discovered an oily derivative of vitamin E in the lungs of patients hospitalized with vaping-related illnesses, a finding the principal deputy director of the Centers for Disease Control and Prevention called a "breakthrough."

The additive, vitamin E acetate, is sometimes used as a diluent of THC oil, particularly by street dealers. THC is the compound in marijuana that produces a “high."

Of 28 lung tissue samples tested, all contained the additive and 23 contained THC.

CDC said Thursday that the outbreak has sickened 2,051 people and resulted in 39 confirmed deaths. The CDC's Dr. Anne Schuchat said Friday that the "trend in cases appears to be downward, but some states are still being hard hit."

The announcement came soon after President Trump told reporters Friday morning that the administration would raising the legal age to purchase electronic cigarettes nationally, likely to 21, in the much-anticipated rule on flavored vaping products to be announced next week.

The legal age for vaping now varies by state with many allowing it at 18 and more increasing it to 21.

“We’re going to be coming out with a very important position on vaping," said Trump. "We have to take care of our kids, most importantly, so we're going to have an age limit of 21, or so."

Also Friday, the Illinois Department of Public Health reported the results of a study that found lung-injury victims were more likely than non-injured vapers to exclusively use THC, buy those products from informal sources such as dealers, street sources or friends, and to vape five or more times a day.

The survey also found that young men were more likely to vape THC products most often. One in four young men aged 18 to 34 reported using THC-containing e-cigarette or vaping products five or more times each day, compared to 13% of similar-aged women.

The overwhelming majority of lung illnesses were in people who vaped nicotine and THC or THC alone, but came as teen nicotine vaping numbers continue to soar which increased pressure on regulators to act.

Federal and state investigators previously found evidence of vitamin E acetate in samples of the substances vaped by the hospitalized patients, but the new results tie the ingredient directly to the injuries. 

Officials use a diagnostic tool called bronchoalveolar lavage, which involves using a bronchoscope in the lungs to collect a fluid sample, to help diagnose vaping-related lung injury. This test identifies a marker of the disease called lipid-laden macrophages, which are cells containing tiny oily droplets.

The National Environmental Health Center's James Pirkle described the additive as being as sticky as honey. That helped explain why it was found it all of the 28 lung samples tested, while THC was found in just 23. Pirkle said that could be easily explained as THC wouldn't necessarily remain in the lungs and urine tests might have been needed to confirm its presence. 

Trump and other administration officials have been lobbied heavily by the vaping industry. A rally is planned for Saturday across from the White House. 

"We have a lot of people to look at, including jobs, frankly, because you know it's become a pretty big industry but we're going to take care of...," said Trump. 

E-cigarette use among high school students more than doubled from 2017 to 2019 to 27.5%. About 5.3 million middle and high school students used e-cigarettes this year, up from 3.6 million in 2018.

Gregory Conley, president of the American Vaping Association, applauded raising the legal purchasing age.

"It appears President Trump is wisely preparing to enact smart regulations rather than embracing the losing politics of prohibition,” Conley said. “Raising the age to purchase tobacco and nicotine products to 21 puts the industry on a similar footing with other adult industries like alcohol and marijuana."

Contributing: John Fritze