In just days, the number of reported vaping-related lung illnesses jumped nearly 40%, but U.S. officials are still stumped at what exactly is making people sick.
The CDC's principal deputy director told reporters Thursday that officials are "working around the clock" to find the cause, saying the investigation "spans many states, involves hundreds of cases and a wide variety of substances and products."
The FDA's Office of Criminal Investigations has also launched a parallel probe involving the products, with a focus on the supply chain.
According to the CDC, a large majority of the 530 cases are in people between the ages of 18-34. And based on preliminary data, most of the people who became ill reported vaping products containing THC, the compound in marijuana that gives users that "high" feeling.
The director of the FDA's Center for Tobacco Products didn't give much more information on the investigation but told reporters the agency is not looking to prosecute people who use vape devices.