Federal health officials say vitamin E acetate is the ingredient suspected in an outbreak of mysterious lung illnesses across the country in recent months.

Officials tested fluid samples from the lungs of 29 patients in 10 states, and found vitamin E acetate – a common supplement that is sometimes used as a vape cartridge additive – in all of the samples. The Washington Post reported that state and federal officials had found the compound in vaping products in early September, but officials had been hesitant to definitively link vitamin E acetate to the lung illnesses without clinical data from patients.

“For the first time, we have detected a potential toxin of concern – vitamin E acetate – in biologic samples from patients,” Dr. Anne Schuchat, the CDC’s principal deputy director, said in a call with reporters. “These findings provide direct evidence of vitamin E acetate at the primary site of injury within the lungs, and the samples reflect patients from states across the country.”