NEW YORK — The number of vaping-related lung illnesses has risen to 530 probable cases according to an update Thursday (Sept 20) by the US Centres for Disease Control and Prevention (CDC), and a Missouri man became the eighth to die from the mysterious ailments.

During a news briefing, Dr Anne Schuchat, principal deputy director of the CDC, said officials expect more deaths because some people are suffering from severe lung illnesses.

But US public health officials said they still were unable to pinpoint the cause, or causes, of the sicknesses that have resulted in hundreds of hospitalisations, with many in intensive care units.

Dr Schuchat 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.

The CDC provided the first demographic snapshot of the afflicted: Nearly three-quarters are male, two-thirds between 18 and 34, and 16 per cent are 18 or younger. “More than half of cases are under 25 years of age,” Schuchat said.

Illnesses have now been reported in 38 US states and one US territory.

In the most recent case, in St Louis, officials said Thursday that a man in his mid-40s who had chronic pain had begun vaping in May. He was hospitalised Aug 22 with respiratory problems and died Wednesday.

“He started out with shortness of breath and it rapidly progressed and deteriorated, developing into what is called acute respiratory distress syndrome,” or ARDS, said Dr Michael Plisco, a critical care pulmonologist at Mercy Hospital St. Louis. “Once the lungs are injured by vaping, we don’t know how quickly it worsens and if it depends on other risk factors.”

He and other officials said they did not know what substance the patient had been vaping, but Dr Plisco said that tissue samples from the lungs showed cells stained with oil.

Some products include oils that if inhaled — even small droplets — can cling to the lungs and airways and cause acute inflammation, doctors have said.

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 flavoured e-cigarettes. Public officials hope restricting flavours that hold particular appeal for youth may discourage teenage use and adoption of vaping. Early results of an annual survey released Wednesday show that teenage vaping has doubled since 2017.

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

The CDC 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 CDC officials continued to emphasize they have not identified a single clear chemical or cause of the outbreak The officials said patients have report using THC, THC and nicotine and for some, just nicotine.

The CDC 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.

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 CDC 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,” 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.”

Mr Eric Lindblom, an expert in tobacco policy at Georgetown Law School and a former FDA senior adviser, said that the FDA has the authority to ban the sale of THC vaping liquid, or THC vape pens, even in states where recreational marijuana is legal — or to ban 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.”

Mr Mitchell Zeller, director of the FDA’s Centre for Tobacco Products it would be premature to take further action until “we get answers to these questions.”

“We are in desperate need of facts and evidence,” he said during a news briefing with the CDC on Thursday. He said that there were multiple compounds showing up in the vaping mixtures, including vitamin E acetate and other additives. He said that vitamin E acetate did not appear to be the sole factor but did not elaborate on other substances involved.

Mr Zeller also said that the FDA’s office of criminal investigations has begun “parallel investigative efforts.” He declined to specify any target of those efforts or whether an enforcement action is forthcoming.

Dr Schuchat from the CDC said she understood the desire for more precise information. “We absolutely want to do that,” she said but added that in providing partial information, officials might “prematurely reassure” consumers about the safety of a product that ultimately turns out to be problematic. THE NEW YORK TIMES