(CNN) The city of Milwaukee issued a stern warning to residents: Stop vaping immediately.
The advisory came after 16 people were hospitalized with chemical pneumonia, a severe illness that causes lung inflammation, the Milwaukee health department said.
All of them reported vaping or "dabbing" -- inhaling potent marijuana products -- before they were hospitalized, the department said.
The link between vaping and respiratory illness isn't fully understood, officials said, but in the meantime, they're advising residents to stop using vapes, e-cigarettes and liquid THC products. Tetrahydrocannabinol, or THC, is the main psychoactive component of marijuana.
Wisconsin health officials said Thursday they're aware of 32 cases of lung disease, including 11 which are still under investigation.
The initial symptoms of chemical pneumonia may not cause alarm: Cough, shortness of breath, fatigue and fever. But the illness can present more severe symptoms, too, like anorexia and chest pain, that worsen in the days leading up to hospitalization, health officials said.
At least 193 cases of lung illness linked to vaping have been reported in 22 states, a number that's growing fast, the Centers for Disease Control and Prevention said last week.
The first vape-related lung illness death came last week. An Illinois man died from lung problems linked to his e-cigarette use, state officials said.
Illinois leads the country in vape-related illnesses, with 22 confirmed cases and 12 more potentials, the CDC said. Wisconsin follows closely behind, and its numbers are growing.
Most of Wisconsin's patients are young people, many of whom were healthy before their hospitalization.
Some of them were so severely ill they were placed on ventilators, respiratory disease epidemiologist Thomas Haupt of Wisconsin's Department of Health Services told CNN earlier this month.
Most of the Wisconsin patients with lung disease linked to vaping said they inhaled THC products, the Wisconsin Department of Health Services said Thursday. Among the 27 cases interviewed so far, 89% reported using e-cigarettes or other vaping devices to use THC products, such as waxes and oils.
"Vaping cartridges containing THC may include chemicals or additives that are unknown, unregulated, and unsafe," said Wisconsin Department of Health Services Secretary-designee Andrea Palm. "We strongly urge people not to vape."
The Wisconsin Department of Health Services said it is continuing to investigate all possible causes, and is working with the US Food and Drug Administration to determine the contents of vaping products.
Though vape use has significantly grown across the US, health officials are most concerned about tackling the "vaping epidemic" among young people.
One in 5 high schoolers use e-cigarettes, the CDC reported. The devices are discrete and come with sweet flavors, which make them more attractive to young people than cigarettes. But while many vapes ditch the tobacco, they often contain just as much nicotine.
North Carolina Attorney General Josh Stein recently filed lawsuits against eight e-cigarette companies for their role in the "vaping epidemic" among middle and high schoolers in the state. The suits accuse the companies of targeting underage users by advertising on social media and flavors reminiscent of candy and ice cream.