A majority of patients with life-threatening lung illnesses linked to vaping say they used products containing THC, and many say they got those products from friends, dealers or elsewhere off the street.

THC is the ingredient in marijuana that produces the drug's high.

The Centers for Disease Control and Prevention, along with public health officials in Illinois and Wisconsin, published details from their investigations into the mysterious illnesses Friday.

The CDC has confirmed 805 cases nationwide, and NBC News has confirmed that hundreds more are under investigation in a total of 47 states.

Interviews with 514 patients reviewed by the CDC revealed some similarities among the cases, but not enough to link any single product, substance or vape brand to the illnesses.

According to the CDC's findings:

77 percent used THC products

57 percent used nicotine products

36 percent used only THC products

16 percent used only nicotine products.

That 16 percent reported vaping only nicotine means investigators cannot say for sure that THC products are behind the illnesses. However, they say some patients may be hesitant to admit using illicit drugs like THC, especially if they live in states where marijuana is illegal.

A closer analysis of 86 patients in Illinois and Wisconsin showed that 87 percent vaped THC. Almost all of those vapes were packaged, pre-filled cartridges that people got from friends, family members or drug dealers.

Meanwhile, the vast majority of those who reported vaping nicotine said they purchased those products from commercial vendors.