The Centers for Disease Control's latest update said 530 cases of the illness have been confirmed.
For people who use nicotine-containing e-cigarettes as a way to quit smoking cigarettes, she urged people not to return to cigarette smoking.
While numerous people who have developed lung problems reported using THC - the active ingredient in cannabis - a number have said they did not vape THC.
Two-thirds of the cases involved 18- to 34-year-olds. More than half of the cases are in people younger than 25. There've been seven confirmed deaths from these illnesses so far, the Post said.
Officials from CDC, FDA and the state of IL described complex investigations, involving hundreds of patients - including some who are reluctant or too ill to talk with investigators - and multiple substances. "Some have reported the use of e-cigarette products containing only nicotine", the CDC said. The probe extends across several states, hundreds of cases and a broad range of products and substances, Anne Schuchat, the CDC's principal deputy director, told reporters on a conference call. But health officials emphasized Thursday that not all people who became ill had used THC, and many had used multiple substances.
Meanwhile, the Food and Drug Administration revealed that its criminal investigations unit started tracking leads early on. Investigators had previously mentioned finding vitamin E acetate in some samples, but lab tests show a "mix of results", Zeller said, and no one ingredient, including vitamin E, has shown up in all of the samples.
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The agency isn't targeting individuals for their personal use of controlled substances through the investigation, according to Mitch Zeller, the director of FDA's Center for Tobacco Products. What's more, "if you recently used an e-cigarette or vaping product and you have symptoms like those reported in this outbreak, we recommend you see a health care provider as soon as possible".
IL has reported an eighth death related to the outbreak, state epidemiologist Jennifer Layden said on a conference call with reporters.
All patients in the recent outbreak now under investigation had used an electronic cigarette or other vaping device.
Layden said the survey might be able to fill in some details to explain why some people become sick and others do not.
"The e-cigarette and vaping-related lung injuries are serious".
She repeated the CDC's advice that people should quit vaping if they can.