The samples, she said, "provided evidence of vitamin E acetate at the primary site of injury in the lungs".
The compound, vitamin E acetate, was previously found in vaping fluid used by many of those who got sick.
"These new findings are significant", Anne Schuchat, CDC principal deputy director, told reporters in a press conference.
The results were published on Friday in the CDC's Morbidity and Mortality Weekly Report.More news: Dozens of out of control bushfires ravage massive areas in Australia
Federal health officials announced on Friday that they'd identified vitamin E acetate, an oil additive found in THC-based vape products, as a "very strong culprit" in the ongoing national outbreak of vaping-related lung illness that has sickened thousands and caused three deaths in MA. People have been vaping for years, so why would users begin having extreme reactions to the products after all this time? As the New York Times reports, the CDC says the finding is based on samples taken from the lungs of 29 of those sickened from vape use.
But the investigation moved away from the acetate as it became clear that the vast majority - 82 percent - of illness-linked samples contained THC, the psychoactive ingredient in cannabis.
Numerous products used by those who became ill were illicitly obtained, public health experts have said, by patients who bought them from friends or on the street.
Health investigators have pointed to Vitamin E acetate as a potential culprit in the illnesses since early on in the outbreak, and health officials in NY earlier reported their suspicion of the ingredient in September.More news: De Minaur, Tiafoe, Kecmanovic reach Next Gen semifinals
So far, there have been 2,051 cases of vaping associated illnesses, reported in every state, except for Alaska, as of November 5. In some instances, it made up more than half of the liquid in the cartridges.
As NBC News reported earlier, numerous lung illnesses have been diagnosed as lipoid pneumonia, in which large amount of lipids, potentially from inhaling vaporized oil, become concentrated in the lungs.
E-cigarettes have been responsible for the deaths of 40 Americans in 24 states (red). The CDC said the lack of THC in five of those samples does not definitively indicate the patients didn't use the drug, because THC can be hard to detect in samples taken from lungs.
Vitamin E is used in several products, such as lotions and in supplements, but the CDC said there is a "big difference" in putting vitamin E on the skin or swallowing it in pill and in inhaling the oily vitamin.More news: Helen Mirren Responds to Keanu Reeves GF Comparisons
Regulators had signaled in recent weeks that the outbreak was likely tied to the use of black-market vaping products containing THC, the pyschoactive ingredient in marijuana, though they hadn't drawn a direct link to any one product, behavior or ingredient.