1) vaping things that really should not be vaped, resulting in oil droplets getting in your lungs. e.g. "cannabidiol oil, which is not designed for vaping but has been used that way." Apparently some vaping fluids are much worse than others, thus the recommendation to "stop buying bootleg and street cannabis and e-cigarette products, and to stop modifying devices to vape adulterated substances."
2) people not seeking timely medical attention and lying about the causes, as marijuana possession is still a crime where they live.
From the article:
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> The patient’s older brother, a police officer, was suspicious. He rummaged through the youth’s room and found hidden vials of marijuana for vaping.
> Health investigators are now trying to determine ... whether the risk stems from a broader behavior, like heavy e-cigarette use, vaping marijuana or a combination
> Many vaping ingredients are not listed on the products. Vitamin E oil appears to have been a common substance associated with the severe and sudden respiratory problems in some of the New York cases, according to state health officials. It is not known how it was used. Vitamin E is sometimes advertised as a supplement in cannabidiol oil, which is not designed for vaping but has been used that way.
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Nicotine is typically in a base of propylene glycol or vegetable glycerine (I think I got those right). I believe both are cheaper than the "adulterants" such as vitamin e oil being used to cut the THC oils, so it is unlikely that people vaping exclusively nicotine products are being affected.
There's been some concern around certain flavorings being much riskier than others (i.e. popcorn lung) though I suspect it'll be some years yet before the effects from those start playing out.