Maryn McKenna

Journalist and Author

Almost Three Times the Risk of Carrying MRSA from Living Near a Mega-Farm

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Pig farms from the air. Image: Maryn McKenna

Pig farms from the air. Image: Maryn McKenna

In the long fight over antibiotic use in agriculture, one of the most contentious points is whether the resistant bacteria that inevitably arise can move off the farm to affect humans. Most of the illnesses that have been associated with farm antibiotic use — resistant foodborne illness, for example — occur so far from farms that opponents of antibiotic control find them easy to dismiss. So whenever a research team can link resistant bacteria found in humans with farms that are close to those humans, it is an important contribution to the debate.

A team from the University of Iowa, Iowa City Veterans Affairs, and Kent State University have done just that. In next month’s Infection Control and Hospital Epidemiology, they survey 1,036 VA patients who lived in rural Iowa and were admitted to the Iowa City facility in 2010 and 2011. Overall, among those patients, 6.8 percent were carrying MRSA, drug-resistant staph, in their nostrils. But the patients’ likelihood of carrying MRSA was 2.76 times higher if they lived within one mile of a farm housing 2,500 or more pigs.
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More on MRSA on Farms and in Farm Workers, and the Arguments for and Against

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Photo: ROIrving/ Flickr

In my last post I promised to catch up on some of the other research that has been published on the flow of MRSA (and other resistant organisms) between farm animals and farm workers as a result of farm antibiotic use.

Before I do that, though, I want to nod toward two other great pieces published on this. First, Mark Bittman  examined this issue closely at the New York Times. And Clare Leschin-Hoar also covered the new research at Take Part. (Bonus: Don’t miss her dissection of the news that a National Geographic photographer was arrested in Kansas after taking pictures of a feedlot — from the air.)

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"Pig MRSA" Carried by Workers from North Carolina Intensive Hog Farms

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Pig farms from the air. Maryn McKenna, Creative Commons License

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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Resistant Bacteria in Pork — And Problematic Pharmaceuticals Too

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Bad news today from an investigation conducted by Consumers Union that was released on the web and will be published in the January issue of the nonprofit’s magazine, Consumer Reports. Tests on pork chops and ground pork, bought in six cities under a variety of labels, showed high rates of contamination with a range of bacteria, many of which were antibiotic-resistant — and also showed evidence of a drug so controversial that it is banned in some other countries.

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