In this April 16, 2019, file photo, a researcher holds vape pens in a lab at Portland State University in in Portland, Ore. As of October 2019, experts who examined lung tissue from 17 patients say lung damage reported in people who use e-cigarettes and other vaping devices looks like chemical burns similar to what you'd see in people exposed to poisonous gases. (AP Photo/Craig Mitchelldyer, File)

U.S. health officials continue to look for patterns in the hundreds of serious lung injuries reported in people who use e-cigarettes and other vaping devices.

A look at what we know so far about the outbreak and the investigation:

WHO IS GETTING SICK?

Health officials say more than half the patients have been male. The average age is about 23, with victims ranging in age from the youngest teens to 72 years old.

WHAT VAPING PRODUCTS ARE INVOLVED?

No single device, ingredient or additive has been identified. Most of the patients say they vaped products containing THC, the high-producing ingredient in marijuana. Others say they vaped both THC and nicotine. A smaller group report they vaped only products containing nicotine.

WHAT ARE THE SYMPTOMS?

Patients are coming into hospitals with cough, chest pain, shortness of breath, fatigue and vomiting. Imaging tests show lung injuries and doctors can't find infections or other causes.

HOW SERIOUS ARE THESE ILLNESSES?

Many of the reports involve severe, life-threatening illnesses in previously healthy people. Many patients received oxygen. Some needed to be put on breathing machines. Antibiotics didn't work, and it's not clear yet whether steroid drugs helped.

WHAT ARE OFFICIALS DOING?

Even before the outbreak, schools were struggling to crack down on vaping because the devices are easy for students to hide. More than 1 in 4 reported vaping in the past month in the most recent government survey. Health officials have warned for years that the popularity of flavored vape products among kids could result in lifelong tobacco use.

With concern about teen vaping already high, the crisis spurred some states to stop the sale of flavored or raise the minimum age for buying electronic cigarettes to 21. Massachusetts suspended sales of all vape products for four months, a move that's been challenged in court. The White House announced plans to ban flavored vape products.

On Thursday, the Federal Trade Commission ordered Juul and five other vaping companies to hand over information about how they market e-cigarettes.

Meanwhile, criminal investigators from the Food and Drug Administration are focusing on the supply chain to find out what's making people sick.

WHAT'S THE LATEST RESEARCH?

It's not final proof, but experts who examined lung tissue from 17 patients say the damage looks like chemical burns, similar to what would be seen in people exposed to poisonous gases. Dr. Brandon Larsen of Mayo Clinic Arizona says he believes toxic fumes are causing at least some of the illnesses. The study was published Wednesday in the New England Journal of Medicine.

HOW DO AMERICANS VIEW THE HEALTH DANGERS OF VAPING AND SMOKING?

Americans believe nicotine is a bigger public health threat than THC, according to a survey by researchers at NORC at the University of Chicago. Nearly all adults (90%) believe smoking cigarettes is harmful, and 81% believe vaping nicotine products is harmful.

Fewer see health dangers in marijuana with 65% saying vaping THC is harmful and 58 percent of adults saying smoking marijuana that contains THC is harmful. The nationally representative survey of more than 1,000 adults was conducted Sept. 19-24.

WHAT DO WE KNOW ABOUT E-CIGARETTE SAFETY?

Health experts generally consider e-cigarettes to be less harmful than traditional cigarettes because they don't contain all the cancer-causing byproducts of burning tobacco. And some countries—including the United Kingdom—have fully embraced vaping as a public health tool to reduce the deadly toll of traditional tobacco.

U.S. health regulators have generally taken a more cautious approach. In part, that's because there is virtually no long-term research on the health effects of the vapor produced when e-cigarettes heat a nicotine solution.

The FDA, which regulates nicotine-vaping products, has set a deadline of next May for all e-cigarette manufacturers to submit their products for review. Under FDA rules, only products that represent a net benefit to public health will be allowed to remain on the market.

WHAT'S THE BEST ADVICE RIGHT NOW?

Health officials are urging people to stop vaping, particularly products that contain THC, and to get medical care if they have trouble breathing or chest pain after .

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