MILWAUKEE (AP) — Wisconsin health officials say about nearly nine out of 10 cases where vaping led to people developing a severe lung disease involved THC products, such as waxes or oils.

The Wisconsin Department of Health Services said Thursday that 89% of the 27 people they interviewed who became sick reported using e-cigarettes or other vaping devices to inhale THC, the psychoactive compound in marijuana.

Health officials say despite the finding they’re still investigating all possible causes for why people became ill with “severe chemical pneumonitis, or chemical pneumonia.” Officials say it’s an inflammation of the lungs due to inhalation of irritants. Health officials say they’re also working with the FDA to determine the contents of used vaping products.

No deaths have been reported in Wisconsin but Illinois reported the first death related to vaping last week.