Friday, June 3, 2011

Multidrug-Resistant Staphylococcus aureus in US Meat and Poultry

Dr. Lance Price is a Senior Scientist, Office of Wellness and Healthy Communities, at the Interdisciplinary Health Policy Institute as well as a Senior Science Advisor at the Pew Charitable Trusts. He is a molecular microbiologist and public health researcher. Lance is also the director of the Center for Metagenomics and Human Health at the Translational Genomics Research Institute (TGen). 

A couple weeks ago we published the first US-based, multi-state study of antibiotic resistant Staphylococcus aureus in retail meat and poultry. We revealed that 47% of the samples were contaminated with S. aureus and that more than half of the isolates were multidrug resistant (i.e., resistant to three or more classes of antibiotics).

I’ve done countless media interviews since the paper appeared online, and the most frequent question that I hear is “What can we do to protect ourselves?” Unfortunately, there’s no straightforward answer to this simple question. We found S. aureus strains with MLST sequence types identical to those of strains that colonize and infect people, but we don’t know if they’re the exact same strains. Even if they were the same strains, we don’t know if meat is a good vehicle for S. aureus infection—anyone who says “it is” or “it is not” is not making their statement based on robust science, because we don’t have good data on this subject yet. Industry groups and the media have largely focused on the risk from ingestion, but we should also be concerned about skin infections from handling the contaminated products. Does having a cut on your hand increase your risk? Maybe. We need to answer this.

I have also read a few statements from people saying that if this were really a problem, we would have seen outbreaks of foodborne infections from contaminated products. I disagree. With such high prevalence rates, we would not expect outbreaks, but rather routine sporadic infections. Campylobacter spp. is a good example of this type of observation. More than 40% of fresh chicken products in the US are contaminated with Campylobacter spp. and a couple million Americans are sporadically infected each year. It’s entirely possible that some of the hundreds of thousands of S. aureus infections that occur in the US each year are from foodborne exposure. So, with all these knowledge gaps, I answer the question, “What can we do to protect ourselves?” by saying what every good public health person would say: “wash your hands repeatedly when handling raw meat and poultry; wash your cutting boards and other equipment; separate meats from vegetables that will be eaten raw; and, definitely cook your food properly.” I also add that people should treat their meat and poultry as potential biohazards and never let children handle these products when helping out in the kitchen.

Unfortunately, almost everyone has focused on the consumer end of the food chain, when the problem clearly starts with the food animal producer. The prevalence of antibiotic-resistant S. aureus antibiotic use in food animal production. on meat and poultry is most likely a result of largely unregulated

While doctors are told to use antibiotics sparingly for their patients, millions of pounds of antibiotics—many of which are important for clinical medicine—are used as common production tools to improve feed efficiency, stimulate growth, and prevent diseases in food animals. I was once told “antibiotics is a crutch for poor animal husbandry” by the owner of a major US poultry production company. I am not a veterinarian, but I can say with confidence that any animal production system that requires the routine input of antibiotics to keep animals from becoming sick is a broken system. There is no justification for this flagrant antibiotic abuse while doctors and scientists are working frantically to preserve the utility of these drugs to treat sick people.

So what’s next? Now that we know that multidrug resistant S. aureus is common in our food supply, we need to define the risk to consumers. Occupational studies are probably the most powerful place to start. Studying food animal workers will tell us about the infectious potential of the strains that we’re finding on our food. Looking at prep cooks and butchers will move us even closer to the risk posed by handling meat and poultry. But, we’ll eventually have to bring these studies to the consumer’s kitchen to see how and how often consumers are exposed to S. aureus from food.

All that said, our future research shouldn’t follow the lead of the media and focus exclusively on the consumer end of the food chain. We also need to better understand the situation in the CAFO and slaughterhouse. How can we decrease antibiotic-resistant S. aureus colonization among food animals in CAFOs? How can we reduce meat contamination in the slaughter facilities? And one urgent question in my mind is: What is the relationship between ceftiofur use and MRSA colonization among food animals? Ceftiofur is a third generation cephalosporin and has been shown to kill off other S. aureus and select directly for MRSA in the laboratory. Are the new MRSA strains—such as ST398—that we are seeing in food animals a direct result of ceftiofur use? We need to answer all of these questions, but we’ll need cooperation by the food animal industry to do so.

Anyway, there are lots of import questions to answer here, and I’d be interested in hearing your thoughts…