As a mysterious lung illness related to vaping sweeps across the nation, add one more mystery to the mix: Colorado, which has the highest youth vaping rate in the nation and also was one of the first states in the country with cannabis vaping products for sale in stores, hasn’t so far seen many documented cases.

The Colorado Department of Public Health and Environment announced Wednesday in its weekly update on the illness that Colorado is now up to six cases of vaping-related lung illness. That’s out of 380 cases nationwide.

Wisconsin, which is similar in population to Colorado, has documented at least 35 cases, according to health officials there. Utah, with fewer people, has reported 42 cases. Neither state has legalized marijuana.

There have been six deaths reported, none in Colorado.

“While we feel even six cases is too many, we really don’t know why Colorado is not seeing more cases in this outbreak yet,” Shannon Barbare, a spokeswoman for CDPHE, wrote in an email. “As we work with our local, state, and national partners to pinpoint a cause of the illness, we hope that becomes clearer.”

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Part of the challenge in documenting cases is just defining what this illness is.

The federal Centers for Disease Control and Prevention has released guidance for confirming cases of the disease, but the symptoms are a little fuzzy. To be diagnosed, a patient must have vaped in the past 90 days and have “pulmonary infiltrate” — i.e. gunk in the lungs — without evidence of a lung infection or other plausible diagnosis.

Colorado health officials are learning about new cases here by asking doctors and local health departments to report them to the state’s disease reporting line.

So far, the only cases identified have been from the broader Denver metro area. Boulder County has seen two, while there has been one each in Arapahoe, Denver, Jefferson and Weld counties.

Colorado’s patients have also skewed young. The median age is 18, with four men and two women. Four of the patients were hospitalized.

In some states, the investigation into the cause of the illness has focused heavily on THC vaping — in Wisconsin, state officials said nearly 90% of the people they identified with the disease had vaped THC. That, in turn, has turned attention to illegally produced cannabis vape cartridges.

But, in Colorado, cases haven’t split so cleanly. In only two instances did the patient vape marijuana only. Three cases involved nicotine vaping only, while another case involved both marijuana and nicotine vaping.

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Still, as the state Health Department has assembled a team of epidemiologists and others to track new cases and search for answers, it is also working with the Colorado Marijuana Enforcement Division. Shannon Gray, a spokeswoman for the division, said regulators there are ready to pull products from the shelves if health investigators identify something in cannabis vaping products that is causing the disease.

In the meantime, health officials are urging Colorado vapers of any substance not to take the risk.

“Our advice has not changed: We want people to quit vaping until we have a clear understanding of what is causing this illness,” Dr. Daniel Shodell, the department’s deputy director of Disease Control and Environmental Epidemiology, said in a statement.

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