A new study by Wayne State University found that 22.5 percent of 289 meat samples from Detroit grocery stores tested positive for Staphyloccus aureus; as well as 20.5 percent of beef, 25 percent of chicken, and 24.6 percent of turkey samples.
Though S. aureus is commonly found on the human body — some studies estimate approximately 20 percent of the population are long-term carriers of the bacteria — methicillin-resistant strains of the pathogen (MRSA) are of increasing concern to the public health community because they are difficult, and expensive, to treat and can cause life-threatening illness.
The Detroit study found 1.3 percent of beef samples, 3.9 percent of chicken samples, and 1.7 percent of turkey samples were carrying MRSA.
“Unlike studies in Europe, where researchers have reported the animal MRSA clone ST398 from various meat products,” reads the study. “All MRSA isolates in our study were USA300, which suggests a possible human source of contamination during meat processing.”
The study comes just weeks after Translational Genomics Research Institute released results of research that found 47 percent of retail meat carried Staph bacteria. In the TGen study, which looked at 136 samples in several states, nearly half the strains of Staph identified were multi-drug resistant, meaning they were resistant to at least three different antibiotics.
The leading trade group for the U.S. meat industry, the American Meat Institute, responded swiftly to the TGen study, which caused a stir in both the mainstream media and the blogosphere. “This small sample is insufficient to reach the sweeping conclusions conveyed in a press release about the study,” the American Meat Institute (AMI) said.
“Calling into question the safety of U.S. beef without conclusive evidence is careless and misleads consumers,” added Bill Donald, president of the National Cattlemen’s Beef Association, in a statement.
Michael Batz, head of Food Safety Programs at the Emerging Pathogens Institute, said in an email that he has conflicting thoughts on the new paper from Wayne State University.
“It’s certainly not a good thing that yet another study has found drug-resistant staph on meat, and it should serve as a reminder that proper handling and cooking are important,” he said. “But I worry that the risk could be overblown. It’s tough to assess the actual risks to consumers because staph is a very common bug that is often transferred person to person.
“Are you more likely to acquire MRSA from meat or from going to the gym? Frankly, we just don’t know.”
Batz said a central concern about MRSA in meat is whether antibiotic use, particularly in pigs, will lead to resistance in animal strains that will then leap to humans (for instance, in workers through small cuts on their hands). One such strain is ST398, known as “pig MRSA” because it was identified in Dutch pigs and pig-workers in 2004.
“This particular study, however, did not find ST398 or any other drug-resistant animal strains, but rather, the common “human” strain of MRSA (USA300) that’s found in hospital and school outbreaks,” he noted of the Detroit research. “Thus, while it’s important information that workers contaminated meat somewhere between slaughter and retail, the paper does suggest anything about antibiotic use on farms.”
It’s unfortunate, Batz added, that information about contamination rates of pathogens on retail meats is available to consumers and food safety practitioners only via these fairly small, one-off studies, and not through any coordinated, ongoing monitoring at the federal level. “These snapshots provide us with a very blurry picture of what is going on,” he said. “We need a more comprehensive approach to surveillance of pathogens in food animals, meat and other foods if we’re to clearly see what’s making people sick.”