Making definitive statements about Clostridium difficile’s evident residency in meat products and livestock is risky at best. Some of the research concerning "C. diff," as it is often called, is worrisome, even frightening; other research much less so. And scientists themselves are quick to point out that at this point what’s not known about a meat connection with C.diff far outweighs what is known.
"Just because C.diff is showing up in food may not mean it’s a problem in food. And as far as C.diff in livestock is concerned, we really don’t know much about the human-animal connection with C.diff. That picture isn’t clear at all," comments Dr. Liz Wagstrom, assistant vice president for science and technology at the National Pork Producers Council. Nonetheless, C.diff in pork and hogs "is something we’ve been following for a long time," she adds.
Dr. Brandi Limbago, the lead researcher for bacterial characterization, typing and identification in the Centers for Disease Control and Prevention’s Clinical and Environmental Microbiology Branch, is only a bit more definite. "We know a fair amount about Clostridium difficile in the health-care environment, and we know it has been found on meat and in livestock, but there are a lot of dots and pieces between these facts that are still blank," she says, noting that studies have found similar strains of C.diff – "some of them indistinguishable from each other" – in humans and food animals. But the microbiologist, who has worked and published with Dr. Glenn Songer at the Univ. of Arizona, one of the world’s leading C.diff researchers, quickly adds: "While it’s very interesting that Clostridium difficile has been found in meat, there’s no evidence that it’s foodborne. To the best of our knowledge, it’s not a foodborne disease."
Songer himself is less sanguine. C.diff, he says, "could be the next O157 – or it could be nothing. I suspect it’ll turn out to be something in between." He adds: "People in the industry really want to know if this is really a problem or not. I understand that. But we have to think it is before we can think it isn’t."
A menace and a killer
The pathogen is a well-known menace in health-care facilities, especially in nursing homes and convalescent hospitals with large populations of older, immune-compromised patients. C.diff infection brings on diarrhea and can lead to dangerous inflammations of the colon – colonitis – if not caught and checked early. Health authorities say it probably causes thousands of deaths, and perhaps tens of thousands of deaths, in health- care facilities every year. (Canadian authorities blame C. diff for roughly 2,000 deaths over 2003 and 2004 in a single province, Quebec.) According to Limbago, as much as 80 percent of all recorded C.diff-caused infections have occurred in a healthcare setting, with human-to-human transmission the most likely distributing vector – but at the same time, she adds, "there are other cases with no health-care connection."
The usual treatment for pathogenic infection, a regimen of antibiotic therapy, is nearly useless against C.difficile, because antibiotics clear out resident microflora and leave behind, in the human gut, a kind of microbiological desert, which C.diff appears to be especially well-equipped for exploiting. According to a study released last November by the Association for Professionals in Infection Control and Epidemiology, 13 out of every 1,000 hospital patients becomes infected by C.diff, a rate up to 20 times greater than had previously been estimated. Just as worrying, a virulent new strain, NAP1, has emerged, and its toxin is 20 times more potent than other strains. Moreover, NAP1 has proven to be resistant to fluoroquinolone antibiotics such as Cipro and Levaquin. It’s a proven killer: A pregnant mother of twins spontaneously aborted and then died from C.diff infection, according to a 2005 CDC review. It is the virulent new strain, however, that has been found on meat and in livestock.
"It’s a very difficult pathogen to get under control," says Dr. David Theno, the recently retired director of technical services at Jack in the Box and one of the industry’s leaders in the battle against E. coli O157:H7. "You’ve got to be really aggressive with it. As the population ages, we’re going to have to figure out a way to effectively deal with it, no question."
According to the Mayo Clinic, "In hospitals and nursing homes, C.difficile spreads mainly on the hands of caregivers, but also on cart handles, bedrails, bedside tables, toilets, sinks, stethoscopes, thermometers – even telephones and remote controls."
A taste for sausage
So what’s it doing in meat? That’s what CDC would like to know. In the effort to come up with an answer, the federal agency called a meeting, in mid-December, of C.diff’s leading researchers and other interested microbiologists and food scientists. The specific purpose of the meeting, according to Dr. Limbago, who attended, "was to discuss methods of detection of Clostridium difficile in foods," but the real driver behind the gathering is the compelling, troubling data gathered by Songer in Arizona, Dr. Scott Weese at the Univ. of Guelph in Canada, and Dr. Roger Harvey, a veterinary medical officer with USDA’s Agricultural Research Service facility in College Station, Texas.
Glenn Songer’s studies are, in some ways, the most worrisome for the meat industry. He found, for the first time, an identical strain of C.diff in contaminated food and in hogs. Moreover, the professor of veterinary science also found that more than 40 percent of packaged-meat samples taken from three Arizona supermarket chains tested positive for the pathogen, and some of these tested positive for the virulent new strain. He calls the results "very surprising." He has detected C.diff’s presence in ground meats as well as in sausages made from ground product, such as fresh pork sausage, chorizo, summer sausage and even liver sausage. He found the bug in half the ground-beef samples he tested and in 62 percent of the brauschweiger. "We haven’t looked at whole-muscle meat yet, but when we do I suspect we’ll find it," he says.
He adds that when he first began investigating C.diff in food a few years ago, "I thought it was a fool’s errand. I couldn’t believe someone hadn’t found it already. I was sure that if it was there, someone would have found it. But it seems like no one did look. And when we finally did, we found it."
Weese’s numbers aren’t quite so shocking, but they remain troubling. His team took C.diff-positive samples from 18 percent of the ground beef and ground veal tested, though they did not find the virulent strain, and the numbers of cells the team found in the positive samples was somewhat lower than what Songer’s team found. Harvey’s work at ARS, and previous work by both Songer and Weese, already found C.diff in dairy calves and pigs, as noted.
"We know we can find it widely in the environment," Weese says. "What we don’t know is how it travels from farms to food. We’ve got a big gap in our knowledge so far."
He points out that C.diff, which was first identified in 1935 (it was originally named "Bacillus difficile," or "the difficult" microbe), is unique among pathogens in a couple of ways. One, it can be found among the gut flora of healthy humans, causing no evident ill effects.
This is why, when the population of C.diff cells suddenly expands (no one knows why), treatment with antibiotics can be so dangerous; with the other microflora pushed out of the way by the drugs, C.diff takes over. Another C.diff’s attribute that’s unique: As a spore-forming microbe rather than a cell-former, it can survive typical cooking temperatures – think of it as a kind of opposite of Listeria monocytogenes, which survives refrigeration.
Still, Weese actually takes some comfort, he says, in the high rates of positives that Songer found in the grocery meats. "In some ways, finding it so commonly downplays the risk. If it’s being found in 40 percent of humans or on 40 percent of meat samples, we know that 40 percent of the human population isn’t getting sick from it."
In search of CCPs
As for meat specifically, Weese isn’t ready to sound alarms. "Meat might be just a carrier, we don’t know. The real problem might always be spreading from human to human, with meat just an intermediary. I don’t think the industry should panic at this point – but we should be concerned." "I can tell you that it’s not coming in to nursing homes on food," adds Dave Theno. "It’s already there. In that environment or in a hospital, it can always move from person to person. We’re talking about a very opportunistic bug."
"We know it can cause illness in baby pigs," says Liz Wagstrom at NPPC. "But C.diff is not C.diff is not C.diff – what I mean is, just because it’s in livestock doesn’t automatically mean meat is a problem. One reason why it may be showing up in ground meats is because those products are handled by more people than other kinds of meat products." She also points out that both Weese’s and Songer’s retail sampling so far has been regional. C.diff’s national and global distribution in meat and livestock isn’t yet mapped. "I think it’s something that we need to look at carefully to see if there’s an emerging problem. But at this point I don’t believe C.diff is our next BSE or O157."
CDC’s Limbago, who will be discussing C. diff at a gathering of meat and animal scientists this coming March, emphasizes that "there’s no epidemiological link" connecting even the "indistinguishable" strains found in livestock and humans. "Animals might be just some kind of reservoir," she says, underscoring Weese’s point. In agreement with virtually all other C.difficile researchers and observers, she says it’s just too early to tell what kind of role meat and livestock play in C.diff’s lifecycle and distribution.
Songer is also cautious about sounding alarms, but he pushes the industry to be proactive. "We can even now probably get ahead of this," he says. "Let’s find the critical control points for this, and let’s take care of them."
This article can also be found in the digital edition of MEAT&POULTRY, February 2009, starting on Page 64. Click