Medical experts and federal health officials warned the public today about the dangers of vaping and discouraged using the devices as the number of people with a severe lung illness linked to vaping more than doubled to 450 possible cases in 33 states and the number of deaths rose to five.

The Indiana Department of Health announced the third death today, and hours later, officials in Minnesota confirmed that a fourth person had died. The Los Angeles County Department of Public Health is investigating a fifth death, and an official said today that “vaping is a probable potential cause.” Two other deaths, one in Illinois, the other in Oregon, had been announced previously.

“There is clearly an epidemic that begs for an urgent response,” Dr. David Christiani of the Harvard T.H. Chan School of Public Health wrote in an editorial published this afternoon in The New England Journal of Medicine.

The editorial called on doctors to discourage their patients from using e-cigarettes and for a broader effort to increase public awareness about “the harmful effects of vaping.” Officials from the Centers for Disease Control and Prevention echoed that call.

The first case of the mysterious lung illness, in Illinois, came in April, indicating that the syndrome emerged earlier than the mid-June date that has been often cited by federal officials as the time the afflictions began.

A keener look at the patient base and syndrome came from details of 53 patients from Illinois and Wisconsin described in the article in the New England Journal of Medicine. The patients were typically “healthy, young, with a median age of 19 years and a majority have been men,” said Dr. Jennifer Layden, chief medical officer and state epidemiologist for the Illinois Department of Public Health.

She said that 98% were hospitalized, half required admission to the intensive care unit, and a third required ventilation. The majority, Layden said, vaped a product including THC, the high-inducing chemical in marijuana, but a majority also used a “nicotine-based product,” noting that there were “a range of products and devices.”

What looked like a few scattered cases in mid-June has become a full-fledged and widespread public health scare, leaving some otherwise healthy teenagers and young adults severely ill.