The number of Americans sickened by mysterious, vaping-related lung illnesses continues to soar as health officials unravel clues to what could be causing these illnesses.

Today (Sept. 6), the Centers for Disease Control and Prevention (CDC) announced that it is aware of 450 possible cases of severe lung illnesses tied to vaping that are under investigation in 33 states. (That’s more than double the number of cases under investigation as of last week.)

Among these cases, three deaths have been confirmed in connection with these illnesses — one each in Illinois, Oregon and Indiana — and a fourth death is under investigation.

Overall, many of the patients are teens or young adults who were previously healthy. All patients reported using e-cigarettes, and many reported using the devices to vape marijuana before they got sick.

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