(CNN) — There have been 530 confirmed and probable cases of lung injuries related to e-cigarettes as of September 17, the US Centers for Disease Control and Prevention said Thursday. That’s 150 more than was reported on September 11.

Still, health officials said they haven’t found a definitive cause or a clear connection between cases, and they warned that patients worried about becoming ill from vaping should refrain from using e-cigarettes.

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There have been vaping-related illnesses in 38 states and one US territory, the CDC said. Among the cases for which patients’ sex and age are available, 72% are in men, 67% are in people ages 18 to 34, 16% are in people younger than 18 and 17% are in people age 35 and older. More than half of the cases are in people younger than 25.

Vaping-related illnesses have been linked to seven deaths — two in California and one each in Kansas, Illinois, Indiana, Minnesota and Oregon. Health officials said Thursday they expect more deaths to be reported.

Officials from CDC, FDA and the state of Illinois described complex investigations, involving hundreds of patients — including some who are reluctant or too ill to talk with investigators — and multiple substances.

“I wish we had more answers,” Dr. Anne Schuchat, principal deputy director of the CDC, said during a media briefing on Thursday.

Hundreds of cases, multiple substances

The CDC and various state health departments have reported widespread use of products containing THC, or tetrahydrocannabinol, the psychoactive substance within cannabis, among people who became ill. But health officials emphasized Thursday that not all people who became ill had used THC, and many had used multiple substances.

Mitch Zeller, director of the US Food and Drug Administration’s Center for Tobacco Products, said the agency has collected more than 150 vaping product samples for analysis in its forensic chemistry center and the number continues to grow. Investigators had previously mentioned finding vitamin E acetate in some samples, but lab tests show a “mix of results,” Zeller said, and no one ingredient, including vitamin E, has shown up in all of the samples.

Zeller also said the FDA has activated its law enforcement arm, the Office of Criminal Investigations for a parallel investigation to identify what is making people sick and how it’s supplied. Zeller said the investigation is ongoing, but the office is not pursuing any prosecutions related to personal use of e-cigarette products.

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Dr. Jennifer Layden, the chief medical officer and state epidemiologist with the Illinois Department of Public Health, said satte investigators have struggled to gather information from patients who are too ill to speak or can’t recall the products they had vaped before becoming ill.

Illinois health officials are asking people who use e-cigarettes — whether they are ill or healthy — to fill out an anonymous survey about their vaping habits.

Layden said the survey might be able to fill in some details to explain why some people become sick and others do not.

Symptoms of vaping illness

Some people — especially youth and young adults, women who are pregnant and adults who do not currently smoke — should not vape, CDC officials said. Adults using e-cigarettes to quit smoking should not return to cigarettes, Schuchat said, but instead should talk to a health care provider about other tools to help them quit.

Health officials urged people not to buy vaping products off the street or modify them.

People who became ill experienced cough, shortness of breath and chest pain, and in some cases, nausea, vomiting, diarrhea and abdominal pain, health officials said.

If people who vape experience symptoms, they should seek medical care.

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