Discovery of C. difficile in meat puzzles scientists
Last Updated: Monday, October 16, 2006 | 10:09 AM ET
The Canadian Press
C. difficile bacteria have been found in a variety of ground and processed meats bought from grocery stores in Canada and the United States, an unexpected discovery some experts say may be linked to recent baffling changes in the pattern of the disease.
Some of the U.S. meats contained the hypervirulent C. difficile strain responsible for severe outbreaks in hospitals in Quebec, Britain and parts of the U.S. over the past few years, the Canadian Press has learned. In Quebec alone, the so-called epidemic strain is blamed for roughly 2,000 deaths in 2003 and 2004.
Though still largely a plague of the elderly in hospitals, C. difficile-associated disease has undergone unexplained shifts of late — some deaths in younger people, more infections outside the hospital. At the same time, there has been a rapid spread of the epidemic strain across North America and to Europe.
Experts keen to figure out what's going on with this bug say the meat finding may provide a clue and must be explored.
More evidence needed
"I don't think we know what it means, but it's a serious concern and it could potentially be contributing to cases, not only in the community but in hospitals as well," said Dr. Dale Gerding, of Hines Veterans Affairs Hospital in Chicago, who was not involved in the research.
But it is too early to conclude people can develop the severe, recurrent and sometimes fatal C. difficile diarrhea by eating meat containing the bacterium, Gerding and other experts insisted.
"The bottom line is that we don't have any evidence to say that C. difficile is a foodborne illness, that people get it from foods," said Dr. Clifford McDonald of the U.S. Centers for Disease Control in Atlanta.
Two teams of researchers — under Dr. Glenn Songer at the University of Arizona and Dr. Scott Weese at the Ontario Veterinary College in Guelph — found C. difficile spores in some samples of ground beef, veal, turkey and pork, pork sausage, chorizo, summer sausage and liverwurst.
Nearly 30 per cent of the meats tested in Arizona (24 of 81 samples) and 18 per cent tested in Ontario (11 of 60) contained C. difficile. The Guelph team did not find the human epidemic strain.
A preliminary report of the Guelph work was to be presented Monday to the World Buiatrics Congress in France. (Buiatrics is the science of treating cattle diseases.)
Each team bought meat over a period of several months from three different grocery stores in Tucson, Ariz., and in the Guelph, Ont., area respectively. The two projects were conducted independently.
The Ontario researchers, who only tested ground beef and ground veal, are currently working on a larger sampling study, including meat bought in Quebec.
Both research teams had already shown C. difficile infects food animals like dairy calves and pigs. And some of the strains found in those animals — and the sampled meat — were virtually identical to some that cause disease in humans.
CDC laboratories confirmed the University of Arizona testing.
The CDC's McDonald said it is a matter of "public health urgency" to find out if meat is playing a role in the worsening profile of disease outbreaks.
No alarm for consumers
"That's one of our priorities, to start doing the types of studies to determine whether people who eat certain foods would be at increased risk over other persons who don't eat those foods," he said.
Songer, a veterinary microbiologist, hadn't expected to find the bacterium when he started the meat testing, so when it turned up in virtually each type of product he sampled, he was startled. He said when he found the epidemic strain.
"I really about had a seizure."
Still, Songer doesn't think consumers should be alarmed at this point. "What we need is more information, not panic."
For one thing, no one knows if this is a new phenomenon, or if C. difficile spores —which are widely dispersed in soil and water — have always found their way into some meats. (Gerding noted though that a study of hospital food in the 1980s did not find C. difficile.)
Earlier this month, Songer and McDonald met with officials of the U.S. Food and Drug Administration and the U.S. Department of Agriculture's Food Safety and Inspection Service to lay out the findings and discuss the need for further research.
Weese, whose lab did the Canadian sampling, said the fact that C. difficile is a spore-forming bacteria heightens the need for answers. Spores can potentially survive cooking, though exposure to temperatures of 80 C for 10 minutes will kill C. difficile, Gerding said.
"It's something we need to explore," said Weese.
"Currently, there is no objective evidence indicating that C. diff is a foodborne pathogen, but the recent changes in C. diff epidemiology and the emergence of C. diff as a community-associated pathogen necessitates looking at areas such as food to explain these changes."
It has been known for about 25 years that C. difficile is a cause of severe and sometimes life-threatening diarrhea in people, typically elderly hospitalized people taking antibiotics. Antibiotics destroy the normal balance of bacteria in the gut, allowing C. difficile to run rampant.
Within the last eight years, though, the pattern of disease has shown signs of shifting.
Hospitals in Pittsburgh, then Quebec, Maine, Florida and later Britain began to report persistent outbreaks with sharply elevated death rates. Some deaths were among younger, previously healthy patients.
More recently, researchers are finding the disease in people who hadn't been hospitalized, many of whom hadn't recently taken antibiotics. How they became infected and why they were susceptible is a puzzle to scientists, who believe that C. difficile cannot cause illness unless the bacterial balance of the gut has been seriously disrupted.
Contributing to epidemic?
Meat may provide some answers, experts acknowledge.
"The question is: Is it contributing to the current epidemic situation? Obviously we don't know whether that's a contributing factor or not," Gerding said.
"But one of the things we've wondered about for years is: How does this epidemic strain get around so readily to such a wide variety of hospitals? And how does it spread from the U.S. to Europe, and country to country in Europe? So this is one possible vehicle for how that might occur."
But until the issue has been studied further, that's just a hypothesis.
"I think we're a long way from saying that meat is an important part of the epidemiology of this disease," said Dr. John Bartlett, of Johns Hopkins Bloomberg School of Public Health in Baltimore.