Federal officials announced today that over 450 people across 33 states and the US Virgin Islands have come down with a deadly lung illness that has been linked to e-cigarette use. That more than doubles the total number of reported cases nationwide — last week, the total stood at 215 possible cases in 25 states.

Officials in Indiana also announced today that a person in their state has died of the disease, bringing the nationwide death toll from the illness to three. The outbreak of the mysterious lung disease is one of two ongoing public health investigations related to e-cigarettes. In addition to trying to uncover the cause of the lung disease, the Food and Drug Administration is also collecting reports on possible seizures related to e-cigarette use.

“We are committed to finding out what is making people sick,” Robert Redfield, director of the Centers for Disease Control and Prevention, said in a statement. “All available information is being carefully analyzed, and these initial findings are helping us narrow the focus of our investigation and get us closer to the answers needed to save lives.”

The exact cause of the illness remains unknown, but investigators think that it is likely related to a chemical exposure, instead of an infectious agent. The New York State Department of Health announced yesterday that a chemical called vitamin E acetate had become “a key focus” of their investigation, and had been found in “nearly all cannabis-containing samples” that the state had tested.

But the investigation is far from over, and vitamin E acetate is one of several possible suspects that authorities are looking into as they try to find the cause of this lung disease.

“Our laboratory is working closely with our federal and state partners to identify the products or substances that may be causing the illnesses and have received more than 120 samples from the states so far,” acting FDA Commissioner Ned Sharpless said in a statement. “The FDA is analyzing these for a broad range of chemicals but no one substance, including Vitamin E acetate, has been identified in all of the samples tested. Importantly, identifying any compounds present in the samples will be one piece of the puzzle but won’t necessarily answer questions about causality, which makes our ongoing work critical.”

In the meantime, health experts are urging people to step away from the vapes. “While this investigation is ongoing, people should consider not using e-cigarette products,” Dana Meaney-Delman, the head of the CDC’s investigation into the illness, said in a briefing, according to The New York Times.

As the investigation continues, a series of articles published in The New England Journal of Medicine (NEJM) today looked deeper into the problem. One article gave a clearer idea of the demographics of the disease, by focusing in on 53 cases reported in Wisconsin and Illinois. The numbers paint a harsh picture.

The researchers found that of the cases, 83 percent were male, and the average age of the patients was just 19 years old. Eighty-four percent of the patients reported using tetrahydrocannabinol (aka THC) before their symptoms set in. Nearly all of them suffered from respiratory and gastrointestinal issues, and 94 percent were hospitalized. One of them died.

An editorial in the NEJM by David Christiani, a professor of medicine at the Harvard T.H. Chan School of Public Health, echoed the CDC’s recent push to discourage people from using e-cigarettes. Christiani said that “efforts should be made to increase public awareness of the harmful effect of vaping, and physicians should discourage their patients from vaping.”