HEALTH officials are warning people not to vape until they determine the cause of a severe respiratory illness, which has killed at least five people and hospitalized many more.

Officials in the US are investigating more than 450 possible cases of a severe breathing illness among otherwise “healthy young people”.

Possible cases have been identified across 33 states and one US territory.

Symptoms of the illness include vomiting, nausea, shortness of breath, coughing and chest pain.

All confirmed cases appear to have a kind of non-infectious pneumonia, called lipoid pneumonia, developed when oil is inhaled.

In all confirmed cases, patients vaped either nicotine or the marijuana constituent THC in the last 90 days.

An estimated 9 million adults and 3.6 million US teenagers vape, including 20% of high school students.

“One of the things found in common was all patients were using vaped substances in e-cigarettes,” said Dr Daniel Fox of WakeMed Health and Hospitals in North Carolina, where several cases were identified.

“They all had abnormal chest x-rays and developed a need for a lot of oxygen.”

Doctors and researchers are still working to determine whether the phenomenon is new, or newly recognized, and how the cases may be connected. So far, no single device, constituent or product has been common across all cases.

They also have not determined the best way to treat the condition. In nearly all cases, the patients were started on antibiotics and many later on steroids, but it is not clear whether these treatments helped patients improve.

Officials asked doctors to collect samples in cases where they suspect a patient could have the ailment. The samples are then sent to the US Food and Drug Administration (FDA).

The FDA is testing more than 120 samples for a “broad range of chemicals”, including “nicotine, THC, cannabinoids, cutting agent or diluents, additives, pesticides, opioids, poisons and toxins”, said Mitch Zeller, director of the Center for Tobacco Products at the FDA.

“FDA is going to leave no stone unturned in following any potential leads,” said Zeller.

The illnesses have all been reported this year, and the number has been growing quickly in the last month as more and more states have begun investigations.

A week ago, US officials pegged the number at 215 possible cases in 25 states. The most recent death due to the illness is in Indiana.

“We’re all wondering if this is new or just newly recognized,” Dr Dana Meaney-Delman of the Centers for Disease Control and Prevention (CDC) told reporters Friday.

Also on Friday, the New England Journal of Medicine released a series of articles which give medical details about cases reported in Illinois, Wisconsin and Utah.

An article on 53 illnesses in Illinois and Wisconsin noted nearly one-fifth of cases were people who said they vaped nicotine alone, and nothing containing marijuana oils.

For that reason, doctors and health officials are continuing to suggest people stay away from all vaping products until the investigation establishes exactly what’s at the root of the illnesses.