I saved this post until today to allow everyone to get their holiday hot dogs guilt-free. Now that’s over: An important study has just been published which makes a close connection between the emergence of antibiotic-resistant bacteria, and the use of antibiotics on large-scale conventional hog farms. Bonus: It involves the resistant bacterium MRSA ST398 (known in shorthand as “pig MRSA”), which is widespread in Europe but up to this point has been found mainly in only one state in the US, Iowa. With this paper, the count rises to two(see Update): The study subjects in this paper are hog-farm workers in eastern North Carolina.

A quick explanation of why this is important: “Pig MRSA” is a particular strain of drug-resistant staph that is slightly different from the hospital and community (sports, gym) varieties. It was first spotted in the Netherlands in 2004, in the toddler daughter of pig farmers and in the family’s pigs. Since then, it has spread widely across Europe, not just in agriculture, but in healthcare and in everyday life, and has also been found widely in retail meat.

The question of whether livestock production’s use of antibiotics causes antibiotic-resistant bacteria to move into the wider world is much argued-over, and pig MRSA, or ST398 to be polite, is crucial to that dispute. That’s because, unlike most resistant bacteria, it has a genetic signature that makes an inarguable link back to farm drug use. More on that below. (If you want more, here’s an archive of my posts on ST398; the story of its emergence in 2004 and what happened afterward is told in my 2010 book SUPERBUG.)

Now, the study. Quick summary, with more unpacking to follow: Researchers checked livestock-farm workers in North Carolina to see whether they were carrying staph, and also drug-resistant staph. The workers formed two groups: one group worked at conventional hog operations, which routinely use antibiotics, and the other group at antibiotic-free farms. Both groups carried staph and also drug-resistant staph, which would be expected; about 30 percent of the population carries sensitive staph and about 4 percent carries the drug-resistant form. But, the key difference: Workers from the conventional, antibiotic-using farms were many times more likely to carry staph with the specific signature of farm-drug use.

That illuminates a potential occupational risk to the workers — and it also suggests that the workers could be a channel for that farm-influenced bacterium to move off the farm.

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