California researchers who tested marijuana sold in Northern California found multiple bacterial and fungal pathogens that can cause serious infections. The study was published this month in the journal Clinical Microbiology and Infection.

The mold and bacteria was so widespread and potentially dangerous that the UC Davis academics concluded that they cannot recommend smoking raw or dried weed. “We cannot recommend inhaling it,” says George Thompson III, an associate professor of clinical medicine at the university who helped conduct the cannabis research.

The findings might also apply to indoor, hydroponic marijuana popular at Southern California collectives, according to Thompson. Using pot in baked goods such as brownies might be “theoretically” safer because the products could be heated enough to kill bacteria and fungus, he says.

Asked if concentrates such as wax, honey oil, dabs and shatter would be safe because heat is involved in the production process of “butane extraction,” Thompson says he isn't sure.

The key finding of the research is that patients with weak immune systems, such as those with HIV or cancer, should avoid smoking raw and dried pot. Though Thompson told the Sacramento Bee that “for the vast majority of cannabis users, this is not of great concern,” he stresses that there really isn't a safe way to smoke marijuana buds, even for those who are healthy.

He says it's possible that filters used with tobacco cigarettes could help with marijuana: Tobacco and all natural plant products have these kinds of bacterial and fungal issues. Irradiated marijuana, though unappealing, also could be an answer, he adds.

Researchers sampled weed samples from Northern California dispensaries and found they tested positive for the fungi Cryptococcus, Mucor and Aspergillus, and for the bacteria E. coli, Klebsiella pneumoniae and Acinetobacter baumannii. The academics said these can lead to serious and lethal illness, noting that smoking the mold and bacteria can embed them directly where they can do the most damage — the lungs.

“Infection with the pathogens we found in medical marijuana could lead to serious illness and even death,” Joseph Tuscano, a professor of internal medicine at UC Davis, said in a statement. “Inhaling marijuana in any form provides a direct portal of entry deep into the lungs, where infection can easily take hold.”

The state Department of Public Health is working on guidelines for marijuana testing with the goal that both medical and recreational pot sold next year at permitted dispensaries would be labeled as safe. It's not clear how this research will affect those guidelines. Thompson says he has reached out to state officials to share his findings.

“We are aware of the study, and while it’s certainly concerning, this is exactly why we need regulation,” Alex Traverso, spokesman for the state Bureau of Medical Cannabis Regulation, said via email. “The Bureau is working with the Department of Public Health to develop strong standards for testing because patient safety is extremely important to us all.”

Edited at 12:24 p.m. Wednesday, Feb. 14, 2017. A quote from the Bureau of Medical Cannabis Regulation's spokesman was added to the story.