Another 121 people have fallen ill and three more people have died from a vaping lung disease that has now sickened 2,172 people and killed 42, the Centers for Disease Control and Prevention said Thursday.

Federal health officials have been trying to control an outbreak of a mysterious lung disease since the summer. They're calling the illness EVALI, short for e-cigarette, or vaping, product use associated lung injury.

The CDC last week reported a possible breakthrough in the investigation. Officials found vitamin E acetate in all 29 lung tissue samples tested, calling the compound a "potential toxin of concern." The oil, typically used in lotions and vitamin supplements, is increasingly emerging in illegal THC vaping products.

Dr. Anne Schuchat, the CDC's principal deputy director, brought a vial of vitamin E to Capitol Hill this week to show the Senate Committee on Health, Education, Labor and Pensions. She and Mitch Zeller, director of the FDA's Center for Tobacco Products, testified on their agencies' response to the outbreak.

FDA labs have received more than 1,000 samples from 25 states, including 850 samples connected to patients, Zeller said. Of the 69 samples from patients that have been examined, 80% contain THC and 75% have vitamin E acetate, he said.

"Lab testing is providing important new information, but no single product, brand, substance or additive has been identified in all of the cases at this point," Schuchat told lawmakers Wednesday. "It may be that there is one cause or that there are many problematic substances causing lung injury. And there may be complex root causes for this outbreak."

Patients who develop EVALI typically report symptoms like coughing, shortness of breath, nausea and fever. The severity of their illness can vary. Doctors in Michigan this week said they performed the first double lung transplant on someone with EVALI, an otherwise healthy 17-year-old boy.

"We know that some individuals will have very long-term damage and not even be able to breathe without new lungs," Schuchat said, referring to the transplant. "But we don't have the full story on the spectrum of illness or of injury or of how people will do."

The FDA and CDC are urging people not to vape THC, the compound that produces a high in marijuana. Most of these products are illegal and unregulated.

Cannabis lab testing company CannaSafe analyzed the vapor produced by illegal cartridges filled with cannabis oil, known as carts, and cartridges sold in California dispensaries. Results found nearly all of the samples contained high levels of vitamin E acetate, as well as "alarmingly high levels" of pesticides.