By Stephanie Stahl

PHILADELPHIA (CBS) — Federal health officials say there’s been a big increase with vaping-related lung illnesses, and now the FDA has a criminal probe underway. While the exact cause hasn’t been determined, it appears most patients used vaping products that contain THC, the active ingredient in marijuana.

Cases are increasing across the country, including in Pennsylvania, New Jersey and Delaware.

The number of cases of lung-related illnesses associated with vaping is growing. Health officials confirm 530 people have gotten sick in 38 states and one territory.

Seven people have died. The Centers for Disease Control and Prevention expects that number to increase.

“We don’t have a single substance product additive or brand that is identified in all of the cases,” CDC Deputy Director Dr. Anne Schuchat said.

While officials can’t pinpoint the exact cause of the illnesses, most patients reported using e-cigarette products containing THC. Seventy-five percent of the cases are male and 66% are people between the ages of 18 and 34.

“Until we know more as this investigation is ongoing, if you have health concerns, we recommend you consider not vaping and not using e-cigarettes,” Schuchat said.

Flavored e-cigarettes are a big concern for health officials since they tend to attract children and teens to vaping. The Trump administration is moving to ban the sale of flavored e-cigs.

The Food and Drug Administration has also tapped its criminal investigators to look into the supply chain, and is analyzing more than 150 samples collected from patients across the country.

Investigators say many of the patients have admitted to using black market or illicit THC products.

Doctors have said the illnesses resemble an inhalation injury, with the lungs apparently reacting to a caustic substance.

Stephanie Stahl