Four cases of severe lung injury in the Twin Cities are being linked to vaping and e-cigarette use, prompting state health officials to warn the public about the harm of these products and to advise doctors to be on the lookout.

The Minnesota Department of Health issued the warning Tuesday after receiving four case reports last week from Children's Minnesota. The teenage patients who suffered the illnesses all were hospitalized for more than one week, with some admitted to intensive care.

While state health authorities have long issued warnings about vaping because of some of the contaminants in e-cigarette cartridges and products, this is the first time they have issued a public notice directly associating the use of these products to patient illnesses.

E-cigarettes "present a danger to our youth, and now we have kids sitting in the hospital that are suffering from lung injuries," said Laura Oliven, tobacco control program manager for the Minnesota Department of Health. "It takes it to a new level of concern."

The illnesses appear to match as many as 12 lung injury cases reported in Wisconsin, and another six in Illinois, but state health authorities said they are still exploring the link to vaping in general, and to the cases in other states. "There are still many unanswered questions, but the health harms emerging from the current epidemic of youth vaping in Minnesota continue to increase," said Dr. Ruth Lynfield, state epidemiologist.

The exact products used by the teens are unknown, but the state noted that some were marijuana-based while others contained nicotine.

Growing popularity E-cigarettes are now more popular among youth than traditional cigarettes, a 2017 Minnesota survey found. 20%: High-schoolers who regularly use e-cigarettes. 40%: High-schoolers who have tried e-cigarettes. 35%: High-school e-cigarette users who used their devices for recreational marijuana or THC.

A vaping advocate said it will be important to identify the specific products before blaming e-cigarettes, especially considering that teens might not be forthcoming about marijuana use that could be the cause of their injuries.

Those who have turned to vaping to wean off cigarettes shouldn't be discouraged by this preliminary news, said Gregory Conley, president of the nonprofit American Vaping Association. "What message are you sending to the 50-year-old smoker in Minnesota who is already inhaling burning smoke into his lungs 20 to 40 different times per day? That's the concern," he said.

Respiratory symptoms are usually due to viruses, or to secondary bacterial infections that can be treated with medications, said Dr. Emily Chapman, Children's chief medical officer. In these cases, the children got worse, not better, during standard treatment. Blood and tissue cultures eventually ruled out viral or bacterial causes of their lung injuries.

"With a virus, you would have expected them to get better on their own, with the support of oxygen and fluids," she said. "They, in fact, did not. They got worse." And in some cases, they suffered a level of lung dysfunction that requires the use of a ventilator to maintain breathing, she added.

For now, state officials have found an "association" between vaping and e-cigarettes and the lung injuries, Lynfield said. Further investigation could prove cause and effect, and determine why teenagers who had vaped before suddenly developed severe symptoms. Perhaps the specific product, or the frequency or amount of vaping played a role, she said.

While vaping has been promoted by manufacturers as a way to wean off traditional cigarettes, health authorities have raised concerns about the contents. Testing has found harmful metals in some e-cigarette cartridges, including nickel, tin and lead.

Despite the warnings, vaping and e-cigarette usage has surged. The U.S. surgeon general has declared e-cigarette usage an epidemic. The 2017 Minnesota Youth Tobacco Survey found that 20% of high school students regularly used e-cigarettes, and that 40% had at least tried them.

Health officials said the sickened teens suffered shortness of breath, fever, cough, and vomiting and diarrhea. They encouraged doctors to monitor for similar cases, and to ask any patients with pulmonary symptoms about tobacco and marijuana use.

"These cases are extremely complex to diagnose, as symptoms can mimic a common infection yet can lead to severe complications and extended hospitalization," Chapman said. "Medical attention is essential; respiratory conditions can continue to decline without proper treatment."

Health officials said they expect reports of more cases in more states now that the outbreaks in the Midwest are receiving public attention.

Chapman said it is possible that vaping-associated lung injuries occurred in the past, but that doctors didn't know to look for them and assumed they were caused by viruses. Differentiating the causes is critical, she said, because patients with infections need their immune systems boosted and supported, whereas patients injured by vaping or other external causes might need their immune systems managed or suppressed.

Boosting the immune system "would be the worst thing that we could do for a patient" in that case, she said.

The four lung injuries all occurred in the last month. The teen patients have all been discharged from the hospital following weeks of treatment. Doctors will be following them to assess any long-term lung damage.