The number of vaping-related lung illnesses has risen to 530 probable cases, and seven deaths are associated with the sickness, according to an update on Thursday by the Centers for Disease Control and Prevention.
But the nation’s public health officials said they still were unable to pinpoint the cause, or causes, of the sicknesses that have resulted in hundreds of hospitalizations, with many in intensive care units.
Dr. Anne Schuchat, principal deputy director of the C.D.C., said officials expect more deaths.
She said some patients are on ventilators and therefore are unable to tell investigators what substances they vaped.
“I wish we had more answers,” she said.
During a briefing with reporters, the C.D.C. provided the first demographic snapshot of the afflicted: Nearly three-quarters are male, two-thirds between 18 and 34. Sixteen percent are 18 or younger. “More than half of cases are under 25 years of age,” Dr. Schuchat said.
Illnesses have now been reported in 38 states, and one United States territory.
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.
Vaping 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 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.
Federal health officials from the C.D.C. and the Food and Drug Administration have said that patients report using different vaping products: THC, THC and nicotine and some just nicotine.
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 F.D.A. 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,” Dr. Michael Siegel, a pediatrician at Boston University who has been a strong advocate for the use 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.
“They’re not releasing the number of cases involved with THC,” he said. “That’s information they should be releasing.”
The C.D.C. has said that, for the time being, people should not vape at all — whether nicotine or THC — to be safe.
Some criticism has been leveled too at the F.D.A., which has been more pointed in its concerns about THC as the chief culprit. But, given that concern, the F.D.A. has not exercised any regulatory effort to stamp out the problem, said Eric Lindblom, an expert in tobacco policy at Georgetown Law School and a former F.D.A. senior adviser.
Mr. Lindblom said that if, in fact, counterfeit THC vaping devices are mostly to blame, then the agency has the ability and even obligation to intervene. Mr. Lindblom said it would be straightforward to disallow the sale of THC vaping liquid, or THC vape pens, even in states where recreational marijuana is legal — or to disallow sales that include any solvents other than ones known to be safe.
“They need to do something,” he said. “They should just take action to stop these things. It’s a no-lose situation.”