Oregon health officials have linked a recent death with an outbreak of vaping-related illness that’s spread throughout the Midwest and West Coast over the past two months.

Since July, hundreds of people have been hospitalized with severe breathing problems after using nicotine or cannabis vapes. Patients have suffered from a range of lung-related issues, including shortness of breath, fatigue, and coughing, and some patients have even required artificial respiration. Last week, an Illinois man died from respiratory complications brought on by vaping, marking the first documented death linked to this cluster of illness.

This week, the Oregon Health Authority (OHA) announced a second death that they also believe is connected to this outbreak. A middle-aged Oregon resident passed away from a severe respiratory illness after using an “e-cigarette or vaping device containing cannabis purchased from a legal cannabis dispensary.” The OHA said that “the individual’s symptoms were consistent with those of more than 200 similar cases in a national cluster of respiratory illness, mostly affecting teenagers and young adults, in at least 25 states.”

Gallery — Here’s What Fake Vapes Actually Look Like:

“We don’t yet know the exact cause of these illnesses — whether they’re caused by contaminants, ingredients in the liquid or something else, such as the device itself,” said Ann Thomas, M.D., public health physician at OHA’s Public Health Division, in a statement.

The US Centers for Disease Control and Prevention is currently investigating 215 potential cases of vaping-induced lung disease in 25 states. Most of these cases are connected to vaping, but beyond that, doctors are stumped as to the exact cause of the illness. Some of these illnesses have been linked to e-cigarettes, while others have been linked to cannabis vapes. Authorities in California and Wisconsin even believe they have traced the cause to specific brands of black market weed vape carts.

In Minnesota, health officials have reported that 15 young adults have recently been hospitalized with sudden lung issues. Eight of these teens reported that they had been vaping cannabis before they became ill. It is still uncertain whether these teens were using black market vapes or state-approved medical marijuana vapes, however. The other nine respiratory cases reported by the state have not been conclusively linked to vaping at this time.

So far, doctors have theorized that the illness might be caused by contamination of vape carts by solvents or heavy metals, or contamination of the vaping liquids themselves by mycotoxins or toxic pesticide residue, but a conclusive explanation has yet to be discovered.