(CNN) -- US health officials announced Friday that they are now aware of at least 450 possible cases of severe lung disease that could be caused by vaping.
These cases, which have occurred in 33 states and one jurisdiction, include some cases that are still under investigation by state health officials.
A third confirmed death was also revealed in Indiana, and a fourth remains under investigation as a possible case. Two other deaths -- one in Illinois and one in Oregon -- had been previously reported.
One week ago, the US Centers for Disease Control and Prevention announced it was aware of at least 215 cases in 25 states, although that number did not include additional cases still under investigation.
The CDC, FDA and state health departments say they're working together to figure out which products might have been used and to facilitate laboratory testing. Health officials say they haven't found a definitive cause or a clear connection between cases, but some are zeroing in on potential clues.
The CDC and various state health departments have reported widespread use of products containing THC, or tetrahydrocannabinol, the psychoactive substance in cannabis.
On Thursday, New York health officials said their investigation had found "very high levels" of the chemical vitamin E acetate in nearly all cannabis-containing vaping products that were analyzed. The chemical is now "a key focus" of the department's investigation into the illnesses.
Mitch Zeller, the director of the FDA's Center for Tobacco Products, told reporters that no one substance, including vitamin E acetate, has been identified in all tested samples. The agency has so far received more than 120 samples showing a broad range of chemicals, he said.
According to health officials, patients have experienced symptoms including difficulty breathing and chest pain before being hospitalized. Some have had other symptoms, such as vomiting, diarrhea, fever and fatigue. Many were previously healthy adolescents and young adults.
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