Why it's so hard to find cause of deaths linked to vaping

Following several mysterious deaths linked to vaping, the federal government is now warning Americans not to use e-cigarettes. The Centers for Disease Control also said there are 450 reported cases of lung illnesses tied to vaping, in more than 30 states. William Brangham talks to Allison Aubrey of NPR about what is known, and what isn’t, about the health risks of vaping.