A mysterious ailment began to affect hundreds of people, causing them to gasp for air, in the spring of 2019. They lived all over the country. Most of them were young and otherwise healthy. But in a matter of days, many became so desperately ill — unable to breathe — that droves of them began showing up in the nation’s emergency rooms. Doctors were perplexed. Antibiotics and steroids were prescribed, but the young victims languished in intensive care units from coast to coast. By summer, the medical mystery quickly turned into a full full-blown epidemic. Over 800 people had become ill and 12 had died. It would turn out that the common thread linking these patients together was vaping. The vast majority were vaping black market THC oil. THC is the psychoactive ingredient in marijuana.