TORONTO - Canadian researchers have found antibiotic-resistant Staph bacteria in pork products purchased in retail stores across the country -- a discovery that raises questions about how the contamination occurred, how frequently it happens and whether it has implications for human health.
Just under 10 per cent of sampled pork chops and ground pork recently purchased in four provinces tested positive for methicillin-resistant Staphylococcus aureus or MRSA, lead researcher Dr. Scott Weese reported Wednesday in a presentation to the International Conference on Emerging Infectious Diseases in Atlanta.
The bacteria would be destroyed by proper cooking, so Staph food poisoning is not a major concern, said Weese, an expert on zoonoses, the pathogens that pass back and forth between people and animals.
But he wondered whether people handling meat with MRSA on its surface would end up inadvertently "colonizing'' themselves. People who carry the bacteria on their skin or in their nostrils are at greater risk of going on to develop a Staph infection, which can range from a hard-to-heal boil to pneumonia to a potentially deadly bloodstream infection.
"My main concern is: if there's MRSA on the surface of a pork chop and someone's handling it and then they touch their nose, could they transmit it from the pork chop to their nose?'' noted Weese, a veterinarian based at the Ontario Veterinary College in Guelph.
"If they do what they're supposed to do in terms of meat handling, then it should be perfectly safe. But do people do that is the question?''
Where MRSA infections were once mainly acquired in hospital, in recent years increasing rates of infections have been recorded in people who haven't been in hospitals and haven't been taking antibiotics.
The startling rise in so-called community acquired MRSA infections in the United States -- a trend which is now being seen in parts of Canada -- has led scientists to look for ways to explain the changing pattern of infections.
But Weese said it is too soon to conclude that MRSA in meat might be playing a role. "It's way too early to say that it does. But we have to look at whether it does.''
"Basically my take-home message is I'm not going to stop eating pork because of this,'' he said. "I'm going to keep washing my hands and pay attention to how I handle it. And that's all I think I need to do.''
This is the first confirmed report of MRSA in retail meat in North America and one of fewer than a handful of such reported findings in the world.
A group of Dutch researchers reported last fall that they had isolated MRSA from two pork samples in the Netherlands. And Japanese scientists reported in 2005 that they had found MRSA in two samples of raw chicken.
Weese's team decided to look for MRSA in pork meat after finding the superbug in Ontario pigs, work that was reported last November in the journal Emerging Infectious Diseases.
He admitted they currently don't know how much significance to place on the presence of the bacteria on the meat. Nor do the testing methods they used allow them to say if the meat was teeming with MRSA, or simply carrying small amounts of the bacteria.
In an interview, he described the research as a step-wise process.
"Step 1 is: Is it in pigs? Step 2: Yes, it's in food. Step 3: ... How much is there? Is it one organism or is it a billion?''
"The techniques we use are fairly sensitive and they don't quantify. It's a Yes-No (answer),'' he explained.
"Now we need to refine that and say: OK, how much is there? Where is it? And in the broad scheme where did it come from and does it actually cause a problem?''
The meat was purchased through the Canadian Integrated Program for Antimicrobial Resistance Surveillance, a Public Health Agency of Canada program that looks for antibiotic resistant bacteria in food and food animals.
To date Weese's team has tested 212 meat samples bought in four different provinces. Most were pork chops but the group also tested a few pork shoulder roasts and some ground pork.
None of the pork roasts carried the bacteria but an equal percentage of pork chops and ground pork did. The rates of positive MRSA tests ranged from zero per cent in one province to 33 per cent in another. Weese didn't want to name the provinces.
Molecular analysis of about half of the isolated bacteria show a mix of strains. Some could not be typed, which suggests they are probably MRSA strains known to infect pigs, Weese said. But of those strains that could be typed, some were of a common human strain while others were of a type known to infect both horses and humans.
