The first case in Canada also emerged this week. Officials there released information about a teenager in Ontario who was put on life support in an intensive care unit, but has now recovered.

The spate of illnesses this summer, coupled with the rising popularity of teenage vaping, has led a few states and the Trump administration to propose outlawing flavored e-cigarettes. Public officials hope restricting flavors that hold particular appeal for youth may discourage teenage use and adoption of vaping. Early results of an annual survey released on Wednesday show that teenage vaping has doubled since 2017.

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Vaping typically entails inhalation of aerosolized substances, usually nicotine or THC — the psychoactive ingredient in marijuana — mixed with solvents or other chemicals.

The C.D.C. reiterated that many of the people who have gotten sick have used THC-based products, some obtained on the street, rather than from retailers in states where recreational or medical marijuana is legal. But C.D.C. officials continued to emphasize they have not identified a single clear chemical or cause of the outbreak. The officials said patients have reported using THC, THC and nicotine and for some, just nicotine.

The C.D.C. has said that to be safe for the time being, people should not vape anything at all. The lack of answers has begun to elicit frustration from various camps, including consumers, policy experts and industry groups. Since mid-August, when public health officials first disclosed that nearly three dozen people had gotten sick, a clear cause has not been identified. The agencies have pointed to the complexity of testing products and challenges of getting detailed history from patients about their behavior.

At the same time, a growing number of critics have said, there should be clearer results from the massive machinery of the federal investigation — more than 80 people at the C.D.C. working on the issue and a Food and Drug Administration lab in Cincinnati working with more than 150 samples from patients who got sick.

“We are not getting specific information we need to protect the public,” said Dr. Michael Siegel, a pediatrician at Boston University who has been a strong advocate for the use of e-cigarettes as a less dangerous alternative to traditional smoking. He said that the government has heavily implied that the problem is largely resulting from the use of illicit THC-related vaping products made but has not exonerated e-cigarettes, creating confusion.