US health officials are investigating what might be causing hundreds of serious breathing illnesses in people who use e-cigarettes and other vaping devices. They have identified about 450 possible cases in 33 states, including six deaths.

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

WHAT ARE THE SYMPTOMS?
Patients are coming into hospitals with cough, chest pain, shortness of breath, fatigue and vomiting.

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 before they recovered. Antibiotics didn’t work, and it’s not clear yet whether steroid drugs helped.

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 only nicotine and others say they vaped both THC and nicotine.

IS THERE A COMMON THREAD?
Doctors suspect chemical exposure. And vape juice contains many possible culprits.

WHAT DID AUTHORITIES FIND?
After testing products, New York has focused its investigation on vitamin E acetate, which recently has been used as a thickener, particularly in black market vape cartridges. Vitamin E is safe as a vitamin pill or to use on the skin, but inhaling oily vitamin E droplets into the lungs can trigger pneumonia.

Immune cells containing oily droplets have been found in the lungs of some patients. University of Utah doctors think this could be a marker for vaping injury, with their findings about six patients appearing in the New England Journal of Medicine.

WHAT ELSE IS IN VAPE LIQUIDS?
Most e-cigarettes contain colourless, flavourless chemicals such as propylene glycol and vegetable glycerine, which create a vapour that can be inhaled when heated. The chemicals are considered safe as food additives but their long-term effects when inhaled have not been studied.

Researchers have found cancer-causing chemicals in e-cigarette vapour, such as formaldehyde. However, it’s not yet clear whether those chemicals are present in high enough amounts to cause harm.

IS THIS BRAND NEW?
There have been occasional reports of similar illnesses, including one from 2000 that was tied to inhaling homemade marijuana-infused oil vapour. The large number of cases is new and alarming to public health officials.

WHO IS INVESTIGATING AND WHAT ARE THEY DOING?
State and federal health officials are testing products and analysing cases for clues, while New York is issuing subpoenas to three companies that sell vaping additives made from vitamin E acetate.

WHAT’S THE BEST ADVICE RIGHT NOW?
Health officials are urging people to stop vaping and to get medical care if they have trouble breathing or chest pain after vaping.

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-with AAP