A potentially fatal bacteria has been found in meats bought in Tucson, triggering a federal investigation to determine if tainted meat is sickening Americans.

The bacteria — known as Clostridium difficile, or C. diff — has been around for decades, but until now was linked mainly to infections in elderly hospital patients taking antibiotics, and never with eating any kind of food.

This is the first time C. diff has ever been found in food, specifically in ground meats. A University of Arizona study made the discovery this year after testing samples — ground beef, ground pork, ground turkey, processed beef and pork products, summer sausage, chorizo and liverwurst — bought in Tucson grocery stores.

However, state and federal health authorities are strongly stressing that the finding, though alarming and certainly surprising, offers no proof that eating meats carrying the bacteria has made or can make anyone sick.

They say it is possible C. diff has always been in the meat supply to some degree, but has posed no danger.

"The discovery of C. difficile in meats is concerning, and the CDC plans to investigate any links between food and infection with the bacteria," said Jennifer Morcone, spokeswoman for the federal Centers for Disease Control and Prevention in Atlanta.

"But at this time, there is no epidemiological evidence showing food consumption to be a risk factor for C. difficile illness. We don't want people to become overly concerned. We are going to conduct our own surveillance of food-borne infections to determine if people have become ill from C. difficile in their food."

The bacteria can cause severe, recurrent and hard-to-treat diarrhea and abdominal cramps. In the worst cases, it can destroy the bowel, and cause death.

Such cases have increased markedly in recent years in the U.S., Canada and Europe, and are showing up among younger, healthy patients who have not been in a hospital or on antibiotics, indicating the bug may be evolving dangerously. Scientists have identified a hypervirulent "epidemic" strain of C. diff they think is causing this phenomenon.

Discovering the bacteria in meats has scientists now wondering if possible food-borne transmission may be playing a role in all this. UA researchers were stunned to find the epidemic strain in several of the meat samples bought and tested in Tucson.

"I was surprised to find difficile at all in meat, but finding the toxic strain of a disease of this importance, well, that was unbelievable," said Dr. Glenn Songer, UA veterinary microbiologist who did the testing.

"This certainly suggests our whole understanding of difficile needs to be re-investigated. At this point, we can't say with certainty this is a food-borne disease, but one way or another we need to find what is causing this in people outside of the hospital, and if there is any connection to what we are eating."

Songer added that his results have not changed his own eating habits, which include meat.

"Not a bit," he said. "It is conceivable a lot of us are cycling difficile through our intestines much of the time without much problem. We need to know a lot more about this before we make any decisions about what we eat. It's far too early to be reacting to this kind of news."

Out of 81 samples of ground meats bought in three unidentified Tucson grocery stores during the past year, Songer found the C. diff bacteria in 30 percent of the samples, and the hypervirulent strain in several of those.

The CDC has retested those samples and confirmed his results, said Dr. Clifford McDonald, a CDC expert in bacterial infections.

"We found these to be the human epidemic strain of C. difficile," McDonald said.

Cases of this dangerous strain — blamed for jumping C. diff death rates from about 1 percent to more than 8 percent — have been found in 23 states, including Arizona, McDonald said.

"We are very interested in what the risk factors for this strain are. We want to know the transmission source, whether certain foods are a risk," he said. "We will get the answer, but it's going to take a little bit of time."

Until then, the CDC is advising only that people vigilantly follow the rules for safe handling of meat, especially thorough cooking — "to the point of complete doneness," he said.

In Arizona, the toxic epidemic strain was identified as the cause of a severe C. diff outbreak a year ago among patients at the Southern Arizona Veterans Affairs Medical Center in Tucson.