Maryn McKenna

Journalist and Author

Drug Resistance in Pork: More Going On Than Appears

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A paper released recently, by the University of Iowa team that is the lone US research group tracking “pig MRSA” ST398, caused a ripple. (It came out while I was at ScienceOnline and it’s taken me a while to catch up.) The paper compares the occurrence of MRSA, drug-resistant staph, on various cuts of retail pork from pigs that were raised either conventionally in confinement, with routine use of antibiotics, or in an alternative rearing scheme with no antibiotics. (NB: Not “organic,” despite what some headlines said; that’s a separate issue of USDA licensure.) The team found that both conventionally raised and antibiotic-free meat carried MRSA, both the human-associated kind and the pig-adapted kind.

The TL;DR over the past week has been: There’s just as much resistant bacteria on drug-free meat as there is on conventional meat, so why spend the money — or raise the alarm over farm antibiotic use?

My interpretation is a little more nuanced. But my takeaway is that, in its underlying data, the study proves what campaigners against ag antibiotic use keep saying: that once you use antibiotics indiscriminately and drive the emergence of resistant organisms, you have no way of predicting where that resistance DNA will end up.

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More MRSA Found In U.S. Retail Meat (Turkey, Too)

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There are two new studies out that confirm, once again, that drug-resistant staph or MRSA — normally thought of as a problem in hospitals and out in everyday life, in schoolkids, sports teams, jails and gyms — is showing up in animals and in the meat those animals become.

The strain of staph that shows up in farm animals, known as “livestock-associated” MRSA or MRSA ST398, first emerged in pigs in the Netherlands, and has been widely identified in retail meat in Europe. (You can find a long archive of posts on ST398 here, and more here.) But that same strain has been difficult to identify in the United States. That may be due in part to the U.S. having a uniquely massive epidemic of community-associated MRSA, far larger than in any other country, which likely both obscures any animal epidemic from detection, and possibly also fills the ecological niche that livestock-associated staph might otherwise occupy. But, it must be said, there’s also remarkably little political will to look for livestock-associated MRSA (though the U.S. Department of Agriculture has now funded a study).

Nevertheless, individual investigators keep trying, and when they look for the pathogen, they find it, such as in these studies from May and this one from April. Now, two other teams have as well.

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More MRSA, in milk: A new strain in cows and humans

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Despite the massive AIDS anniversary this week, I was expecting to write about the EU E. coli outbreak next. But there’s striking new news on MRSA that makes it worth putting off E. coli one more day. I’m traveling many time zones away from home, though, so this will be quick.

Researchers in England and Denmark have announced they have found a never-before recorded variant of MRSA in cow’s milk in England that has already caused human infections in England, Scotland and Denmark, and researchers in Ireland have simultaneously announced that they have found the same strain in hospitalized patients there as well.

Here’s how this unfolded:

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MRSA in meat: How much? Which? And more bad news.

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(Sorry for the radio silence, constant listeners. It’s been a challenging few weeks at Casa Superbug, with a death in the family and the chaos afterward of catching up to the rest of life. But back now, with some interesting stuff planned for later this week.)

Last week was the General Meeting of the American Society for Microbiology (ASM). This is the conference at which, several years ago, Tara Smith’s team at the University of Iowa first announced they had found MRSA ST398 in pigs in the United States, so it always bears watching for new MRSA news, and this year it didn’t disappoint.

First: I’ve complained persistently because the federal system that monitors antibiotic-resistant bacteria in animals and food, NARMS (National Antimicrobial Resistance Monitoring System) doesn’t include MRSA among the pathogens that it tracks. It is possible that might be changing — because at ASM, a team from the Food and Drug Administration reported the results of a pilot study that looked for MRSA in retail meat in the US and found it.

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Farm Antibiotics: 'Pig Staph' in a Daycare Worker

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It’s been just about seven years since an alert epidemiologist in the Dutch town of Nijmegen identified an aberrant strain of MRSA, drug-resistant staph, in a toddler who was going in for surgery to fix a hole in her heart. The strain was odd because it didn’t behave normally on the standard identifying tests, and because it had an unusual resistance factor — to tetracycline, a drug that it should not have been resistant to, because the Netherlands had such low rates of MRSA that tetracycline wasn’t being used against the bacterium there.

Pursuing the source of the strain, researchers at Radboud University found it in the toddler’s parents and sister, and in the family’s friends. Not knowing where else to look, they asked what the parents and their friends did for a living; discovered they were all pig farmers; and went to their farms, and checked the pigs, and found it being carried by them, too. Suddenly, that strange resistance pattern made sense: The Netherlands uses more antibiotics in pig agriculture than any other country in the European Union, and the drug that it uses the most is tetracycline. Clearly, the aberrant strain — known as MRSA ST398 for its performance on a particular identifying test — at some point had wandered into pigs, become resistant to the drugs being given to the pigs, and then crossed back to humans, carrying that new resistance factor as it went.

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Multi-Drug Resistant Staph in 1 in 4 Meat Samples

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Much of the contentious debate over abuse of antibiotics in farming boils down to a couple of simple questions: Whether resistant organisms that arise on farms because of antibiotic use leave the farm, and whether, once they do, they reach human beings.

A piece of research due to be released this morning in the journal Clinical Infectious Diseases helps answer both those questions. (I received an advance copy under embargo; I’ll put up the link when the journal posts it. here’s the link to the full-text pdf.)

A team of researchers from Arizona bought meat and poultry in five cities across the United States, tested them for bacteria, and found this: 47 percent of the samples contained the very common pathogen Staphylococcus aureus, and 96 percent of those isolates were resistant to at least one antibiotic. Of more concern: 52 percent of those staph isolates were resistant to at least three antibiotics that are commonly used in both veterinary and human medicine.

That is: Roughly one in four packages of meat and poultry from across the United States contained multidrug resistant staph. [Read more…]

Opposing industrial-scale pig farming — in Europe

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Well, wow. National legislators stand up to oppose the use of tax revenues to subsidize large-scale confinement pig farms out of concern for food safety and antibiotic resistance, declaring that they are “going to war in defense of pigs.”

In Europe, though.

At the European Parliament today, three national representatives — Janusz Wojciechowski of Poland, José Bové of France and Dan Jørgensen of Denmark — declared their opposition to industrial-scale swine agriculture, positioning themselves for a fight over the European Union’s Common Agriculture Policy, which is up for revision this summer.

Jørgensen represents the country that has done the most to place controls on agricultural antibiotic use; Bové is a farmer and political organizer who famously destroyed a McDonald’s by driving a tractor through it; and Wojciechowski is the son of pig farmers who wrote on his blog today:

Chcemy poruszyć sumienia posłów i doprowadzic do likwidacji tego typu “fabryk miesa” w Unii Europejskiej, no czywiscie takze w Polsce, gdzie takich fabryk jest juz ponad sto.
Chcemy doprorowadzic do tego, aby wielkie fermy nie były wspierane środkami europejskimi, aby wstrzymać lokalizacje nowych obiektów, po czym stopniowo likwidować te, które już istnieją.
Chcemy, żeby na miejsce fabryk miesa powróciła normalna hodowla świń.
We want to move the conscience of members and lead to the liquidation of this type of “meat factories” in the European Union, also in Poland, where such plants are already over a hundred.
We want to ensure that large farms are not supported by the European funds to stop the locations of new facilities, then gradually eliminate those that already exist.
We want “meat factories” returned to normal breeding of pigs. (via GoogleTranslate)

As I’ve written before (long archive here and here),the MRSA strain ST398 arose on Dutch pig farms in 2004, among pigs that had been given prophylactic doses of antibiotics, especially tetracycline. It has since spread through the EU, Canada and the United States, affecting not only farm workers and veterinarians, but also hospital patients with no connection to agriculture.

(Self-promotion alert: This may be a good time to tell you that my book SUPERBUG: The Fatal Menace of MRSA, which tells the full story of the emergence and spread of ST398, has just been released in paperback.)

In advance, this morning the trade paper Farming UK wrote this about the planned European Parliament announcements:

(Members of the European Parliament) will hear evidence that European taxpayers’ money is being used by the European Bank for Reconstruction and Development, together with Common Agriculture Policy payments, to subsidise industrial pig farming even though there is increasing concern over the impact on human health. With a vote this summer over reforms to the Common Agricultural Policy, MEPs will come together to take a stance against the crisis in agriculture with critically low prices for pork, poor labelling, and widespread disregard for animal welfare laws.

MEPs and NGOs will condemn the overuse of antibiotics in factory farms which has led to the emergence of antibiotic-resistant bacteria such as MRSA and ESBL E. coli. A recent report by the Dutch Food Standards Agency estimated that one third to one half of all antibiotic resistance in human diseases in the Netherlands derives from farm antibiotic use. American scientists recently found that flies and cockroaches from intensive pig farms carry bacteria resistant to the same antibiotics routinely used in pig farming, and warned that the insects were likely to be able to spread the disease from the farms to local people.

The event was co-organized by Tracy Worcester, who is both a British aristocrat and director of a documentary, Pig Business, that has not yet been shown in the US. Here’s its trailer:

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In both medicine and agriculture, Europe has been ahead of the US in addressing concerns about antibiotic resistance. This morning’s announcements are yet more evidence of just how far ahead they are.

Flickr/VickyTGAW/CC

Farm worker infections with MRSA — the first numbers

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Since the first identification in 2004 of MRSA ST398, also known as “pig MRSA” or livestock-associated MRSA (archives of posts here and here), that drug-resistant organism has been found being carried asymptomatically by farm workers and veterinarians, and causing illness in health care workers, hospital patients, and people with no known ties to agriculture. One of the persistent data gaps, though, has been whether farm workers themselves have been made sick by it.

It’s a difficult question to answer for a nested set of reasons: First, in most of the states, MRSA (methicillin-resistant Staphylococcus aureus, or drug-resistant staph) is not a reportable disease; that is, a doctor who diagnoses it in a patient is under no obligation to tell any public health authority about that patient’s case. And second, the testing required to distinguish livestock-associated MRSA from community-acquired or hospital-acquired is not something that primary-care medical personnel have access to; you have to go to a state laboratory or an academic medical center to do the appropriate molecular typing. Those tests are expensive to perform, and their results primarily are useful to public health, not to individual medical practitioners. So finding out where that nascent epidemic is going has been unusually challenging.

Comes now a team from the University of Iowa — the same team that first identified ST398 in pigs and pig-farm personnel in the United States — to start to fill the gap. [Read more…]

"Pig MRSA": New human infections in France

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It’s one of the touchiest topics under the broad category of antibiotic resistance: Whether the drug-resistant organisms that emerge on farms as a result of antibiotic use stay on farms, or pose a risk to humans who have no connection to agriculture.

That drug resistance emerges under any selective pressure is basic biology: Resistance is an inevitable process. That they emerge on farms when antibiotics are used broadly — that is, in growth-promoting or prophylactic ways, not to treat disease in individual animals — really isn’t in dispute any more. It’s now a question of economics and politics, not science. (See this bibliography, stretching back to 1969; and the news I broke yesterday of FDA’s estimate of US farms using almost 29 million pounds of antibiotics last year.)

So the argument over farm antibiotic use now tends to focus on whether the resistant organisms that emerge on farms are only an issue within a farm’s confines, or rather pose a broader human health threat — and that’s where the continuing story of the “third epidemic” of MRSA becomes so important. Recapping, this is a strain known as MRSA ST398 that emerged in pigs and passed to pig farmers in the Netherlands in 2004, subsequently spread across the European Union, and crossed to Canada and then to the United States. (Key posts on ST398: here, here, here and this archive at my old site. Yes, it will be moved soon, promise.)

Most of the identifications of MRSA ST398 in humans, including those first identifications above, were colonizations, the term for symptomless carriage of staph in the nostrils and on the skin; in other words, it wasn’t making people sick. News of actual illnesses has been rare — especially illnesses among people who have no contact with farming, such as the post-surgical infections found in Canada earlier this year.

But they’re getting a little less rare, as demonstrated by a letter just posted ahead-of-print to the journal Clinical Infectious Diseases. It recounts the finding, via annual surveys of bloodstream infections, of four cases of ST398 in four different hospitals in France. One may have been due to animal exposure. Three were hospital-acquired.

Examination of patient histories revealed exposure to animals in 1 case, a fatal idiopathic community-acquired bloodstream infection in an 84-year-old man who lived on a farm at which 1 pig was being raised. The remaining cases were hospital-acquired and included 1 case of catheter-associated infection observed in a 58-year-old man with advanced multiple myeloma, 1 case following elective digestive tract surgery in a 69-year-old woman, and 1 case following cardiac surgery in a 68-year-old man.

There’s an especially interesting thing about these cases. In Europe and the US, ST398 has particular characteristics: It is resistant to tetracycline (the drug most commonly given to pigs) and does not manufacture the toxin Panton-Valentine leukocidin or PVL, which is suspected to be a cause of community-strain MRSA’s uncommon virulence. (See this story, from the book SUPERBUG, of how PVL-positive pneumonia almost killed a toddler.) The strain in the French cases, though, does manufacture PVL, and shares some virulence characteristics with the dominant community strain, USA300. It is less like the European strain of livestock-associated MRSA and more like a livestock-associated strain that appears to be emerging in China, ST9 (more on that here).

The argument against the significance of these cases is likely to be that they are, again, just one data-point, and may be just rare and random. That is worth considering. But it is also worth considering that they continue to be found.

And, also, that the community epidemic of MRSA was first flagged in a discovery of 25 cases in children in Chicago back in 1998, a finding that was also dismissed at the time as rare and random — and that grew into an epidemic of millions of cases a year.

(H/t to constant reader Pat Gardiner for flagging this paper for me.)

Cite: van der Mee-Marquet N et al. Emergence of Unusual Bloodstream Infections Associated with Pig-Borne–Like Staphylococcus aureus ST398 in France. Clin Infect Dis. (2011) 52 (1): 152-153. doi: 10.1093/cid/ciq053

Image via Flickr user johnmuk under CC

Alarm over "pig MRSA" — but not in the US

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There’s some new news out — along with a fair amount of public reaction — regarding “pig MRSA” or, to use the technical term, MRSA ST398, the “third epidemic” strain that emerged in pigs in the Netherlands in 2004 and has since appeared, in animals, retail meat, and humans, across the European Union, in Canada, and in the United States. (My last post on it is here, and a long archive of my posts on it starts here.)

I wish I could say the attention to ST398 was being paid in the United States, where there is almost certainly more MRSA in livestock than has been recorded, given that the only published surveillance, from 2009, covered only Iowa and Illinois. Unfortunately, there is still no indication that federal agencies have any intention to test for the presence of the organism in animals or in meat. In fact, the major surveillance mechanism for drug-resistant organisms in meat animals, retail meat and meat-eaters in the US, the National Antimicrobial Resistance Monitoring System or NARMS, doesn’t test for MRSA at all; it handles only enteric or gut-borne bacteria such as Salmonella and Campylobacter. (NARMS IS shared among three agencies: the CDC handles drug-resistant foodborne bacteria in humans, the FDA looks for the same bacteria in food, and the USDA looks for those bacteria being carried by livestock.)

Instead, as so often seems to happen with antibiotic resistance, the country paying attention is in Scandinavia — in this case, Denmark. The annual report from Denmark’s surveillance scheme, DANMAP (Danish Integrated Antimicrobial Resistance Monitoring and Research Programme) is out. Denmark does surveil for MRSA, and here’s what they found: 13% of pigs, at slaughter, were positive for MRSA ST398.
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