Antibiotic Resistance Myth Busting: Stop Blaming Livestock for MRSA

In July, a journal named PLOS ONE published  a study led by Johns Hopkins Bloomberg School of Public Health and the University of North Carolina titled, “Livestock-Associated Methicillin and Multidrug Resistant Staphylococcus aureus Is Present among Industrial, Not Antibiotic-Free Livestock Operation Workers in North Carolina.”

The politicized, fear-mongering headline automatically caused me to approach the article with a healthy level of cynicism, and the first paragraph in the publication markedly increased my thinking that the 10 authors had some serious biases against the animal agriculture industry.

In that first paragraph, the authors define the two sets of workers whose nasal passages they cultured for Staphylococcus aureus, also known as Staph, as those working in “industrial livestock operations” (ILOs) and those working in “antibiotic-free livestock operations” (AFLOs).

If you are raising animals for human consumption, you are part of the agriculture industry. If you are raising hogs and chickens in a confined facility, you are part of the conventional livestock operations. The words “industrial” and “antibiotic-free” are obviously meant to influence readers to picture this as a story is about the bad guys (ILOs) vs. the good guys (AFLOs).

We have seen how carefully chosen inflammatory words, like “Pink Slime,” can agitate the public. The very first sentence of the article states that, “Administration of antibiotics to food animals may select for drug-resistant pathogens of clinical significance, such as methicillin resistant Staphylococcal aureus (MRSA).”

MRSA has been around since 1960, one year after methicillin was first prescribed for use in human medicine. For the next 40 years, nearly every single case of MRSA was hospital acquired. It is predominantly a human health related pathogen. Methicillin is not used in animal health. To suggest that antibiotic use in animals is the cause of this menace is far from an accurate, scientific statement.

The ILO workers featured in the study worked in confined operations, in very close contact with hogs eight hours every working day. Just as humans pass their germs to other humans, it should be no surprise that human to animal and animal to human passage may occur if exposure is high enough. The AFLO workers were outdoors among hogs and chickens with very little actual contact with any animal during the working day. Each of the two groups had nasal carriage prevalence of Staph aureus of approximately 40 percent. This is the same as the U.S. population rates of carriage. No story here.

The two groups each had three people (3 percent) test positive for MRSA. This is consistent with the prevalence of MRSA in the U.S. population in general. No story here either.

The authors make a big deal that they can prove that the three individuals in the ILO group had livestock associated-MRSA (LA-MRSA) and that the three in the AFLO had community-acquired MRSA. The authors emphasize that some of the Staph isolates were resistant to more than one antibiotic. The antibiotics they tested for and found resistance to included penicillin, ampicillin and tetracycline.

In 1960, 80 percent of all hospital Staph isolates were already resistant to penicillin. I don’t care if the Staph is resistant to penicillin, ampicillin and tetracycline making them multidrug-resistant Staph by definition. That is a finding of zero human health significance.

What is significant is that this study found no resistance in any of the Staph bacteria to vancomycin or linezolid, the two drugs of choice to treat MRSA. Ninety-three percent of the Staph showed susceptibility to methicillin. Because of prior Food and Drug Administration (FDA) actions to protect the integrity of these powerful antibiotics to treat serious human infections, our health care providers still have effective weapons against Staph aureus. This finding should have been the headline and the story.

Another attempt to mislead reads, “Despite current understanding of livestock-associated MRSA as a relatively rare cause of human infection in the United States…” It is not “relatively rare” in the U.S. It is zero. There has never been a documented human case of LA-MRSA in the United States.

There is a significant difference between “rare” and “zero.” It is rare to be struck by lightning, but since it does occur, we need to be careful in storms. It is rare to win the lottery, but since it does happen, we buy tickets. If the hogs could type, they would probably pen a blog blaming us for giving them MRSA, not the other way around.

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