Federal health officials said nearly 77% of cases of patients with vaping-related lung injuries had used products containing THC, adding to evidence that such vaping devices and cartridges are lead suspects in the widening epidemic.

“The outbreak is currently pointing to a greater concern around THC containing products,” said Anne Schuchat, principal deputy director of the U.S. Centers for Disease Control and Prevention, on a call with reporters on Friday. THC is the main psychoactive ingredient in marijuana.

However, she emphasized that the agency couldn’t rule out that nicotine-containing products were risky, and said that no one product or substance has been used by all patients with vaping-related lung damage.

The number of vaping-related lung-injury cases stands at 805, up from 530 reported a week earlier, the CDC said Thursday. Twelve people have died, according to the CDC’s tally, though the Oregon Health Authority reported another death, the second in the state, on Thursday, and warned people to “stop vaping immediately.”

Part of the CDC’s investigation involved getting information from patients on what products they used -- information that isn’t always available or reliable. Of the 514 patients where CDC has some information about the products used, more than three-quarters used products containing THC.

Thirty-six percent exclusively used THC products, while only 16% used nicotine containing products exclusively.

Other research published Friday shows just how complicated it is to narrow down the range of possible culprits for the outbreak.

In a separate analysis of patients in Wisconsin and Illinois, two states where injuries were recognized early on, 86 patients interviewed reported using 234 unique products with 87 different brand names.

This article was provided by Bloomberg News.