Maryn McKenna

Journalist and Author

MRSA and pets

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It’s been a while since we’ve focused on the presence of MRSA strains in pets, and the complications that can cause for the pets’ human owners/custodians/companions (or, in the view of my own two cats, abject servants. No, I will not post their pictures. I have some shreds of pride).

The problem with MRSA and pets is not the same as the problem of MRSA ST398 in food animals. Rather, pets tend to carry human strains, passed to them by their owners. The carriage is usually asymptomatic, but not always; there are cases in the medical literature of cats and dogs suffering serious skin and soft-tissue infections from community-strain MRSA, usually USA300. But the emerging consensus seems to be that pets carry the bug transiently — not long, but long enough to reinfect the person who passed the bacterium to the pet in the first place. (This can be, but is not always, the source of recurrent infections in humans: The human takes antibiotics and recovers, but the animal holds onto the bug long enough to pass it back to the now-clear human.)

For anyone who needs to go deeper on this, the current issue of Lancet Infectious Diseases has a good overview of the problem that community MRSA strains pose to pets and their humans. There’s a thorough review of the major papers:

  • Cefai, 1994: hospital outbreaks traced to two nurses and through them to their dog
  • Simoons-Smit, 2000: household epidemic of three humans, one cat, one dog
  • Manian, 2003; dog is source for owner’s recurrences
  • Vitale, 2006: owner is (apparently) source of cat’s MRSA.

(This is a good place to say that this entire history, including personal stories of human and animal infection, is covered in a chapter of SUPERBUG. Publication date coming soon!)

The Lancet paper incorporates reminders of some powerful and troubling trends. As with MRSA ST398, one thing can distinguish MRSA that has been in an animal is a resistance pattern that is slightly different from what we expect but that has arisen because the animals receive different drugs. In the case of pigs and ST398, the intriguing marker is tetracycline resistance; humans don’t usually get tetracycline for MRSA, but pigs do. In the case of companion animals, it tends to be fluoroquinolone resistance; pets are more likely to get that class of drugs for a skin/soft-tissue infection. But, the authors caution, that may mean that pets serve as a breeding ground for multi-drug resistant MRSA, with their fluoroquinolone treatment adding another resistance factor into the bug’s already potent arsenal.

The authors also remind us that MRSA can come from animals much more directly than through silent carriage: that is, in a bite. Both dog and cat bites have been found infected with MRSA, due to bacterial contamination of the wound either from the pet or from colonization on the human’s skin.

The cite is: Oehler RL et al. Bite-related and septic syndromes caused by cats and dogs. The Lancet Infectious Diseases, 9(7):439 – 447, July 2009. doi:10.1016/S1473-3099(09)70110-0.

H1N1 flu and swine surveillance – more relevance for MRSA

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Constant readers, you probably know that yesterday the World Health Organization declared the first flu pandemic in 41 years. I want to point out for you a side issue in the H1N1 story that has great relevance for MRSA, especially ST398.

As described in this article I wrote last night for CIDRAP, three medical journal articles have now pointed out that the virus, or its major components, could have been recognized in swine months to years ago. We missed it, though, because there is so little regular surveillance in pigs for diseases of potential importance to humans. As the authors of the most recent article, in Nature, said yesterday: “Despite widespread influenza surveillance in humans, the lack of systematic swine surveillance allowed for the undetected persistence and evolution of this potentially pandemic strain for many years.”

This is important for our purposes because we know that we are in the same situation with MRSA ST398: The strain was first spotted in France, and has been a particular research project in the Netherlands, but has been found pretty much wherever researchers have looked for it, throughout the European Union, in Canada, and most recently in the United States. All told, though, the scientists concerned with it are still a small community; there is no broad surveillance looking for this bug.

And that’s a problem, for MRSA, for influenza, and for any number of other potentially zonotic diseases: We cannot anticipate the movement of pathogens from animals to humans if we don’t know what’s in the animals to start with. That’s the argument behind the “One Health” movement, which has been arguing for several years now for including veterinary concerns in human health planning. (The human health side would probably say that the animal health side just wants more money. This is also true, which does not make it unimportant.)

To understand the need to look at animal health in order to forecast threats to human health, you can’t do better than the map I’ve inserted above (because Blogger, annoyingly, won’t let me put it below). It has appeared in various forms in various publications for about 10 years but originates I think from the IOM’s Emerging and Reemerging Diseases report in the early 90s. (This iteration comes from the One Health Initiative website.) It depicts the movement of new diseases from animals to humans over about 30 years. It’s up-to-date through SARS and through the 2003-05 movement of H5N1 avian flu around the world. I’m sure H1N1 will be added soon. How many of those outbreaks could we have shortcircuited if we had been warned of their threat in good time?

Farm animals and antibiotics – a new campaign

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I was gobsmacked to discover today, a few days late, that the Pew Campaign on Human Health and Industrial Farming (authors of the report discussed here) have launched a marvelously in-your-face series of ads in Washington DC, aimed at bringing the issue of antibiotic use in farm animals to people who might not think about it.

The ads have been placed in the Capitol South and Union Station Metro stops, which are the stops that bracket Capitol Hill, and in Metro cars on the red and blue/orange line trains, which are the main commuter trains down to the Hill. In other words, they’ve been made to be the morning reading of the people most engaged in the health reform debate right now — and if you think those folks are not thinking about healthcare spending and the growth of antibiotic resistance, well, umm, oh never mind.

The campaign says:

The American Medical Association, the American Academy of Pediatrics and other leading medical groups agree that the growth of bacterial infections resistant to antibiotic treatment is a looming public health challenge. The groups also agree the misuse of antibiotics on industrial animal farms plays a significant role in this crisis. While antibiotics are prescribed to people for short-term disease treatment, these same critically important drugs—like tetracycline, erythromycin and ciproflaxin—are fed in low doses to large herds or flocks daily, often for the lifespan of the animal. This creates ideal conditions for the breeding of new and dangerous antibiotic-resistant bacteria.

For statistics and arguments, along with more images — cows! chickens! pills! — go to the site of the commission’s campaign, Save Antibiotics.

MRSA in pig-farm workers – very high rates

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Let’s go back for a moment to what I think of as the “third epidemic” of MRSA: ST398 and the other strains that reside in animals and cross to humans. (In my personal taxonomy, the first and second epidemics are hospital-acquired and community-associated.)

Via Emerging Infectious Diseases, the open-access journal published by the CDC (Do I have to keep telling you to read it? It’s free. It’s good. Your tax dollars pay for it.), comes a report of surveillance for MRSA colonization of pig-farm workers, conducted in Belgium by researchers from Erasmus Hospital of the Free University of Brussels, and the Veterinary and Agrochemical Research Centre of Brussels. The group persuaded 127 farm workers on 49 farms to be tested for colonization, or asymptomatic carriage, of MRSA; at the same time, they tested 30 randomly selected pigs on each farm.

They found very high rates of colonization, higher than have been found in patients in hospitals or residents of nursing homes: 38% of the farm workers carried MRSA ST398, the pig strain (plus, an additional 17% carried various strains of MSSA, drug-susceptible staph). There was a clear association between colonized farmers and colonized pigs: Out of 1500 pigs sampled, 44% carried ST398 — and half of the workers on farms with colonized pigs were colonized also, compared to only 3% of workers on farms where pigs did not carry the bug.

In a bit of good news, the researchers found only one farm worker who had suffered any MRSA disease from ST398, a man with a lesion on his hand. There was no invasive disease, though ST398 has been associated in the past with pneumonia and endocarditis.

Workers were more likely to acquire the bug if they had regular contact with pigs, dogs or horses, which makes intuitive sense. But in an odd finding, their odds of acquiring ST398 did not go down if they wore protective clothing — which is to say, aprons, gloves and masks did not protect them from picking up the bug, leading the researchers to wonder whether airborne spread or contaminated surfaces are playing a role in transmission.

So what does this mean? The lack of invasive disease in this population must be good news; and it’s consistent with a number of papers that have reported low rates of disease from ST398 even when colonization is present. But to me, the high rate of colonization must be bad news. The more of this bug there is (and every researcher who looks for it seems to find it), the more chance there is of the bug adapting in an unpredictable — potentialy more resistant, potentially more virulent — way. If that did happen, it could well go undetected for a while — because as swine flu has been teaching us, disease surveillance in animals is patchy at best, and new pathogens can and do arise and ciruclate for years before being detected.

For more on the paucity of surveillance in animals, see my CIDRAP colleague Lisa Schnirring’s story here. For a complete archive of posts on “pig MRSA” ST398, go here.

The cite is: Denis O, Suetens C, Hallin M, Catry B, Ramboer I, Dispas M, et al. Methicillin-resistant Staphylococcus aureus ST398 in swine farm personnel, Belgium. Emerg Infect Dis. 2009 Jul; [Epub ahead of print] DOI: 10.3201/eid1507.080652.

MRSA in the House of Lords — the silly, the serious

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Thanks to constant reader Pat Gardiner, we have the transcript of the UK House of Lords discussion on community MRSA, called there PVL-MRSA after the toxin. (Go to the linked page, and click down to the time-mark 3.16 pm.) It’s encouraging to see some members of a government taking MRSA seriously. The members are asking for

  • better surveillance
  • better infection control
  • consideration of MRSA as a notifiable disease
  • and promotion of both vaccine research and point-of-care diagnostics.

Hear, hear to Baroness Masham of Ilton for bringing it up.

To get to that discussion, though, you’ll have to click down through some silliness (the ghost of Monty Python is never far from the British government, is it?): a discussion at time-stamp 3.07 p.m. of whether a House of Lords restaurant can afford to serve British bacon, rather than Dutch bacon, given that British bacon is almost twice as expensive and Dutch pigs are associated with MRSA ST398:

Lord Hoyle: My Lords, I thank the noble Lord for that reply, although there is more than a whiff of hypocrisy about it. After all, I and many others on all sides of the House have argued that it should not be a matter of price. We have urged the British consumer to buy British bacon because of the higher welfare standards that are applied in this country. Will the noble Lord also take into account the presence in Dutch bacon of a deadly form of MRSA, ST398, which can cause skin infection, heart trouble and pneumonia? Is he not putting people in this country at risk, particularly as the strain has passed from animals to humans? Indeed, when Dutch farmers go into hospital, they go into isolation. Why is he putting the British consumer and those who buy bacon in this House at risk in this way?

The discussion quickly devolves into foolishness about British Tomato Week — but if you read carefully, you’ll see that behind the silliness, there are serious issues at stake: animal welfare, farming standards, truth in labeling (the Lord Bishop of Exeter advances the very newsworthy claim that pork imported from other countries is subsequently labeled “British” only because it is packaged in the UK) and movement of zoonotic pathogens across national borders thanks to globalized trade.

Sadly, the leader of the discussion — the Chairman of Committees, AKA Lord Brabazon of Tara (no, really) — appears not to have been keeping up with the news, since he notes of ST398:

As far as MRSA is concerned, I read the article in, I think, the Daily Express a couple of weeks ago. I do not think that it has been followed up by anybody else.

Apparently the Lord’s staff have not been keeping up, since MRSA in pigs in the EU has been covered by the Daily Mail, the Independent, comprehensively by the Soil Association, and by, ahem, us.

ST398 found again — in Italy

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There’s a letter in the upcoming issue of Emerging Infectious Diseases (hat tip Pat Gardiner) alerting the medical community that “pig MRSA” ST398 has been found in Italy, adding t the steadily enlarging list of countries where this strain has been identified.

(NB: Because most of these surveys are one-offs, we don’t yet know whether ST398 is truly expanding its range, or has always been there, but no one looked until now.)

Angelo Pan and colleagues of the Cremona Hospital and other institutions report that a pig-farm worker was discovered to have a severe pyomyositis (abscess buried in muscle):

The case-patient was a 58-year-old man admitted to a surgical department in Cremona, Italy, on July 30, 2007, because of a 1-week history of fever and intense pain in his right buttock. He worked on a pig farm, was obese, consumed high volumes of wine (1.5 L/day), was taking medication for hypertension, and had not had recent (<5 years) contact with the healthcare system. At the time of hospital admission, he was moderately ill, oriented, and cooperative. His right buttock was extremely painful. He reported neither recent trauma nor anything that would explain infection. ...
Based on clinical and magnetic resonance imaging data, the diagnosis was cellulitis, pyomyositis, and pelvic multiloculated abscess of the buttock. A needle aspiration of the abscess, guided by computed tomography, was performed. Because of persistent fever (38.5°C), oral ciprofloxacin was added to the patient’s treatment regimen on day 3. Blood and abscess cultures yielded MRSA that was sensitive to glycopeptides, rifampin, linezolid, gentamicin, and mupirocin and resistant to co-trimoxazole, macrolides, clindamycin, and fluoroquinolones. After treatment was switched to vancomycin plus rifampin, the patient’s general condition improved; he was discharged from the hospital after 24 days.

An investigation was launched, and the results were intriguing:

Two fellow workers were colonized with S. aureus, 1 with methicillin-sensitive S. aureus (MSSA) and the other with MRSA. The pig farm, a farrow-to-finish production farm with 3,500 pigs, was screened for MRSA … Dust swabs were taken from 5 areas of the farm; 7 MRSA isolates were detected.
The isolate from the patient belonged to spa type t899, was ST398, carried an SCCmec type IVa cassette, and was PVL negative. The isolate from the MRSA-colonized worker was a t108 strain carrying SCCmec type V. The isolate from the MSSA-colonized worker was identified as t899. The dust swabs yielded 7 isolates: 2 belonged to t899 and carried SCCmec IVa; 5 belonged to t108 and carryied SCCmec V. The isolates obtained from the patient, farrowing area 7, and gestation area 1 were indistinguishable (i.e., same spa type, SCCmec type, and ST profile; Table), thus confirming the animal origin of transmission.

So, we have:

  • A high rate of carriage on the farm (3 of 4 workers with ST398, either MR or MS)
  • A strain-type that is both MRSA and MSSA, suggesting that in its drug-sensitive state it can acquire resistance factors rather easily
  • A PVL-negative strain that nevertheless causes invasive disease requiring more than 3 weeks hospitalization

None of these are good news.

The authors very sensibly call for more public-health attention to this strain, which — we have contended before — is long overdue:

…attention should be given to the emergence of MRSA strains among animals, and continuous surveillance in humans should monitor the extent of disease from MRSA ST398, especially in areas of intensive animal farming. Collaboration between infectious disease specialists, microbiologists, and epidemiologists, on both the human and the veterinary sides, should be strengthened and readied for appropriate action whenever complex, zoonotic, public health issues occur.

The cite is: Pan A, Battisti A, Zoncada A, Bernieri F, Boldini M, Franco A, et al. Community-acquired methicillin-resistant Staphylococcus aureus ST398 infection, Italy [letter]. Emerg Infect Dis [serial on the Internet]. 2009 May. DOI: 10.3201/eid1505.081417

More news on ST398, “pig MRSA,” in Europe

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Two new papers have been posted ahead-of-print to the website of Emerging Infectious Diseases, the free journal published monthly by the CDC. (It’s a great journal. Just go.)

One, from the Austrian National Reference Center for Nosocomial Infections, reports that out of 1,098 isolates from infected or colonized hospital patients collected between 2006 and 2008, 21 were ST398, the “pig strain” that we have talked so much about here. Of the 21, 15 were colonized and 5 had actual infections (one person lost to followup, apparently); of the 5 infections, 4 were minor, and one was a very serious infection in a knee replacement in a 64-year-old farmer.

In a separate piece of math that is not fully explained, the researchers note that the prevalence of ST398 in Austria has risen to 2.5% of MRSA isolations, from 1.3% at the end of 2006 — close to double, and especially rapid given that Austria’s very first ST398 sample was found during 2006.

The second paper is much more complex; it deals with the prevalence of multiple MRSA strains in the cross-border region where Germany, Belgium and the Netherlands bump up. (Apparently EU bureaucracy calls an area like this a “Euregio.” Ah, jargon. This is the EMR, the Euregio Meuse-Rhin.) The concern here is that MRSA prevalence is very different in different EU countries; in the Netherlands, which has an active surveillance “search and destroy” policy in its hospitals, MRSA represents only 0.6% of all staph — but the rates are 13.8% in Germany and 23.6% in Belgium, which either do not do active surveillance or began to much more recently. So as people move freely across borders, from a high-prevalence area to a low-prevalence one, they could bring a resistant bug with them that then could find a foothold because there is an open ecological niche.

This study analyzed 257 MRSA isolates from hospitals in the border region that were collected between July 2005 and April 2006: 44 from Belgium, 92 from Germany, and 121 from the Netherlands. Of the Dutch isolates, according to typing, 12 (10%) were ST398. These were all from patients who were identified as colonized when they checked into hospitals practicing “search and destroy”; none represented actual infections.

So, what does this tell us? A couple of things, I think. First, it documents the continued presence of ST398 in Europe; in other words, it wasn’t a blip and doesn’t appear to be going away. Second, it underlines both that you find it when you look for it, and also that it remains a small portion of the overall MRSA picture. But, we immediately have to add, it’s a small portion that wasn’t present at all just a few years ago.

And it should underline that what we need, and are not getting in this country or in Europe, is much more comprehensive surveillance and research to understand ST398’s place in MRSA’s natural history, so that we can understand where it is only an emerging disease, or truly an emerging threat.

The cites are:
Krziwanek K, Metz-Gercek S, Mittermayer H. Methicillin-resistant Staphylococcus aureus ST398 from human patients, Upper Austria. Emerg Infect Dis. 2009 May; [Epub ahead of print]
Deurenberg RH, Nulens E, Valvatne H, et al. Cross-border dissemination of methicillin-resistant Staphylococcus aureus, Euregio Meuse-Rhin region. Emerg Infect Dis. 2009 May; [Epub ahead of print]

Bill in Congress: “Preservation of Antibiotics for Medical Treatment” Act

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Important news for anyone concerned about the spread of “pig MRSA” ST398: Rep. Louise Slaughter (D-NY) and Sen. Edward Kennedy (D-MA) have introduced a bill that would restrict important classes of antibiotics for use against disease only, taking them out of the realm of subtherapeutic use or growth promotion in agriculture. The bill would allow the use of the antibiotic classes for disease in animals as well as in humans; the intent is to preserve the drugs’ effectiveness for as long as possible.

The text of the bill, the Preservation of Antibiotics for Medical Treatment Act of 2009, is here.

A Reuters story in which Slaughter predicts the bill will have a difficult time is here; she has introduced it several times in the past decade, but it has never made it through.

Support from the Pew Commission on Industrial Farm Animal Production is here. An earlier version was supported by the American Academy of Family Physicians here.

The National Pork Producers’ Council’s response is here.

(Hat tip to Barry Estabrook at Politics of the Plate and to Melinda Hemmelgarn, the FoodSleuth.)

MRSA and animals — an elephant, this time.

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So, constant readers, I have wrestled another chapter to the ground — and thus have a few minutes’ breathing space to talk about a story that some of you have asked about privately. I’ve been wondering whether to post on this, because the entire episode is in the book, and I don’t want to scoop myself. But it’s so interesting, and so sad, that it seems worthwhile.

This episode happened a year ago, and was reported at a couple of medical meetings last fall, but it is in the news now because it was written up last week in the CDC’s Morbidity and Mortality Weekly Report or MMWR. (Which is the best-read magazine that you have never heard of. Hundreds of thousands of people all over the world read it every week for the latest in disease news. It’s free. Go, already.)

So, the brief synopsis: In late January 2008, the San Diego Zoo’s Wild Animal Park noticed that a baby African elephant, born in late November 2007, had broken out in pustules on her ear, neck, elbow and leg. Three of her caretakers had skin infections also. The zoo launched an investigation, assisted by a CDC Epidemic Intelligence Service officer who is assigned to California; they were concerned that the caretakers had unknowingly picked up a disease from the baby, who had been born early, was not thriving and was being intensively hand-reared by the zoo staff.

But in fact, it was more complicated than that. The pustules were MRSA, of course — but they were not ST 398, the animal strain that we have talked about so much here. Instead, they were USA300, the community-associated human strain that has zoomed to dominance all over the country. But there was no MRSA in the elephant herd, which the baby had not had contact with since late December. The reconstructed chain of transmission looked more like this: from an unknowingly colonized human to the baby elephant, who was medically fragile and had been isolated from her herd, and then from the elephant to the rest of the human “herd” who were caring for her. The strain involved was USA300, In the end, five human infections and three colonizations were laboratory-confirmed, and 15 other infections were suspected but not confirmed.

The humans recovered; most of their infections were so minor as to need no treatment, though three of them took oral antibiotics. The poor little elephant was not so lucky. She had multiple other illnesses, and she was euthanized on Feb. 4, 2008. The MRSA did not cause her death — by the time she died, the infection had resolved — but as one of the zoo staff told me, “It certainly didn’t help.”

So what does this tell us? Well, for zoo personnel, it tells them what to do for next time: More complete infection control especially around vulnerable animals. For microbiologists, it’s an expansion of MRSA’s range: No one had ever seen it in an elephant before.

For animal owners, it’s a warning and reminder. We’ve known for a while that community strains can transiently colonize pets, staying in the animal’s nose or elsewhere on the body just long enough to reinfect a human — in fact, an emerging piece of advice for physicians dealing with recurrent MRSA in families is, “Check the dogs and cats, too.”

And for the rest of us, it suggests, one more time, how extremely adaptive and inventive MRSA is, and that we should never underestimate its ability to surprise.

More MRSA, more meat – poultry, this time

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Constant readers: Fresh from the journal Emerging Infectious Diseases — posted AOP (electronic publication/ahead of print) this afternoon — comes more news of MRSA ST 398, the “pig strain,” in food animals. This time, it’s chickens, in Belgium.

The authors (from Ghent University and the Veterinary and Agrochemical Research Center in Brussels) took swabs from living chickens — laying hens and broilers — from 24 farms, 50 layers and 75 broilers total; one broiler-raising farm was sampled twice. They found no MRSA in the layers, which is important for reasons I’ll get to in a moment, and ST 398 in 8 broilers. From each chicken, they took two samples, nasal and cloacal, and in the 8 positive chickens, they got 15 MRSA isolations; one cloacal swab was negative. Of the positive chickens, several (I deduce three, but the math is a bit cloudy) were spread across the two visits to the farm that was sampled twice. Since chicken farms are depopulated between batches — yes, just what it sounds like, farms sell/kill all the birds and clean the place — that finding suggests that MRSA is persisting in the environment on that farm.

Important point: This strain was ST 398, which we here have been calling the pig strain from many previous findings, most of them in pigs. However, ST 398 is an identification using a particular technique called MLST (multi-locus sequence typing), which is used for this strain because the standard typing method, PFGE (pulsed-field gel electrophoresis), did not return a readable result when the strain was first identfied back in 2004. (Trivia: That’s why the initial reports of this strain called it NT, for “nontypeable.”) It’s becoming increasingly clear, though, that ST 398 is actually a category, not a single strain. And within that category, today’s research is a new find: a strain with the unusual spa type t1456, which has only been found 10 times in the past three years, in Germany and the Netherlands, not in Belgium. The author suggest that this particular strain may be adapting to poultry in the same manner that the ST 398 we have been talking about (different spa type — sorry, I will have to look it up) has adapted to pigs.

So, as before: Why do we care? We care for two reasons: First, because since this strain is in a food animal, the possibility exists that it could contaminate the chickens’ meat during slaughter and pass to humans. As has happened with some ST 398, the humans could be only colonized, and not become ill. But, second, any increase in colonization is a bad thing: The more strains out there, the greater the chance that they will exchange virulence and resistance factors and become something unpredictable.

Now, about those layers, here’s an interesting factor that the authors call out in their paper: Layers, unlike broilers, do not receive antibiotics. The layers did not carry MRSA. The broilers did. It’s a pretty potent argument, in case anyone needed convincing, of the effect of the selective pressure that antibiotic use in food animals exerts on these strains.

The site is: Persoons D, Van Hoorebeke S, Hermans K, Butaye P, de Kruif A, Haesebrouck F, et al. Methicillin-resistant Staphylococcus aureus in poultry. Emerg Infect Dis. 2009 Mar; [Epub ahead of print] DOI: 10.3201/eid1503.080696

Appearing tonight at SciAm.com

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Folks, last summer I told you about the very exciting though disturbing development of ST 398 MRSA — the “untypable” Dutch strain that originated in pigs and spread to humans — being found in pigs in the US for the first time.

But here’s the brand-new second half of that story: It was found in pig handlers as well, on a set of linked farms — a closed production system that takes pigs from birth to just before slaughter — in Iowa and Illinois.

The full study has just been published, in the online Public Library of Science journal PLoS One.

And I have a story describing the research and the background — and the alarming spread of ST 398 in Europe — up tonight at ScientificAmerican.com.

The cite is: Smith, TC, Male, MJ, Harper, AL et al. Methicillin-Resistant Staphylococcus aureus (MRSA) Strain ST398 Is Present in Midwestern U.S. Swine and Swine Workers. PLoS ONE 4(1): e4258 doi:10.1371/journal.pone.0004258

UPDATE: Lead author Tara Smith talks about the paper at her own blog, Aetiology. And for good measure, her Science Blogs sibling (AKA “scibling”) Ed Yong discusses the paper at Not Exactly Rocket Science.

MRSA in meat in Louisiana: pig meat, human strain

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On Nov. 3, I posted on an enterprising group of TV stations in the Pacific Northwest who had retail meat in four states tested for MRSA. I said at the time that it was the first finding of MRSA in meat in the US that I knew of.

Turns out that I was wrong by three days. On Oct. 31, the journal Applied and Environmental Microbiology published an electronic version of a study that they will be printing in the paper journal on some future date. Journals do this when a finding is so important or timely that it should see the light immediately, rather than wait through the additional weeks or months of print production.

And this finding is certainly timely. Shuaihua Pu, Feifei Han, and Beilei Ge of the Louisiana State University Agricultural Center have made what appears to be the first scientifically valid identification of MRSA in retail meat in the United States. But — and this is an important point — it is not the swine strain, ST 398, that has been found in meat in Canada and Europe, and in hospital patients in Scotland and the Netherlands, and in pigs in Iowa; and in humans in New York, though that strain was drug-sensitive.

Instead, what the researchers found (in 5 pork and 1 beef samples, out of 120 bought in 30 grocery stores in Baton Rouge, La. over 6 weeks in February-March 2008) was USA300, the dominant community MRSA strain, and USA100, the main hospital-infection strain. In other words, they found meat that had been contaminated during production by an infected or colonized human, not by a pig. As they say:

…the presence of MRSA in meats may pose a potential threat of infection to individuals who handle the food. … (G)reat attention needs to be taken to prevent the introduction of MRSA from human carriers onto the meats they handle and thereby spreading the pathogen.

As we’ve discussed before, the primary danger from MRSA in meat is not that people will take the bug in by mouth (though that is a danger, since S. aureus because of its toxin production can cause severe foodborne illness — and these researchers found, overall, an S. aureus contamination rate of 46% of their pork samples and 20% of their beef samples). Rather, the danger is that people handling the raw meat will be careless in preparing it, and will colonize themselves by touching the meat and then touching their own noses or mucous membranes, leading to a possible future infection. As reader Rhoda pointed out in a comment last week, people could also infect themselves directly, by getting MRSA-laden juice or blood into an abrasion or cut.

So: Be careful in the kitchen, keep meat separate from other foods, wash cutting boards and knives, and (say it with me, now) wash your hands, wash your hands, wash your hands.

The cite for the new paper: Pu, S. et al. Isolation and Characterization of Methicillin-Resistant Staphylococcus aureus from Louisiana Retail Meats. Appl. Environ. Microbiol. doi:10.1128/AEM.01110-08. Epub ahead of print 31 Oct 08.

Housekeeping note: This is the 16th post I’ve written on MRSA in food animals and/or meat. Providing all the links to the previous posts is starting to obstruct the new news. So if you are looking for all those past posts, go to the labels at the end of this post, below the time-stamp, and click on “food.” You should get something that looks like this.

Final report from ICAAC-IDSA 08 (news from ICAAC, 3)

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The ICAAC-IDSA (48th Interscience Conference on Antimicrobial Agents and Chemotherapy and 46th annual meeting of the Infectious Diseases Society of America) meeting ended a week ago, and I’m still thrashing my way through the thousands of abstracts.

Here’s my final, highly unscientific selection of papers that caught my eye:

* Evidence that the community-strain clone USA300 is a formidable pathogen: It first appeared in the San Francisco jail in 2001. By last year, it had become the sole MRSA strain found in the jail — it crowded out all others. (P. Tattevin, abstract C2-225)
* Another paper from the same UCSF research group finds that the emergence of USA300 has caused a dramatic increase in bloodstream infections, most of which are diagnosed in the ER, not after patients are admitted to the hospital. (B. Diep, abstract C2-226)
* And the CDC finds that USA300 is picking up additional resistance factors, to clindamycin, tetracycline and mupirocin, the active ingredient in the decolonization ointment Bactroban. (L. McDougal, abstract C1-166)
* An example of the complexity of “search and destroy,” the active surveillance and testing program that seeks to identify colonized patients before they transmit the bug to others in a health care institution: Patients spread the bug within hours, often before test results judging them positive have been returned from the lab. (S. Chang, abstract K-3379b)
* In addition to the report from Spain I posted on during the meeting, there is a report of emerging linezolid resistance in France. (F. Doucet-Populaire, abstract C1-188)
* And in addition to the abundant new news about MRSA in pork, and “pork-MRSA” or ST 398, in humans, over the past few days, there were reports of MRSA in milk in Brazil (W. Gebreyes, abstract C2-1829) and Turkey (S. Turkyilmaz, abstract C2-1832), and beef and chicken in Korea (YJ Kim, abstract C2-1831), as well as ST 398 itself acquiring resistance to additional drugs. (Kehrenberg, abstract C1-171)
* Echoing many earlier findings that MRSA seems most common among the poor, the poorly housed and the incarcerated, BR Makos of the University of Texas found that children are more likely to be diagnosed with the bug if they are indigent, or from the South (which I imagine is a proxy for lower socio-economic status, since the South is a more rural, more poor region). (abstract G2-1314)
* And finally, to the long list of objects (ER curtains, stethoscopes) that harbor MRSA, here are more: The ultrasound probes in emergency rooms (B. Wessman, abstract K-3377). Also: Dentures. (Ick.) (D. Ready, abstract K-3354)

TV stations find MRSA in retail pork in Pacific Northwest

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In the comments, Coilin Nunan of the UK’s Soil Association (which published the wonderful 2007 report MRSA in Farm Animals and Meat report) calls attention to a report that I also spotted over the weekend.

A network of TV stations in Washington, Idaho, Oregon and California did a joint report in which they bought 97 packages of ground pork or pork cutlets and sent them to a laboratory for testing. The lab found that three of the packages, all ground pork, contained MRSA.

I believe this is the first time anyone has found (or, perhaps, looked for) MRSA in retail pork in the US. You’ll remember that MRSA ST 398 has been found in meat in Canada and Europe, and in hospital patients in Scotland and the Netherlands, and in pigs in Iowa; and MSSA ST 398 in humans in New York City.

There are some important unanswered questions about this report:

  • We aren’t told the strain. If it’s ST 398, that would be information on the spread of ST 398 in the US. If it’s USA300, on the other hand, it could be contamination from an infected or colonized human, perhaps someone in the preparation chain.
  • We aren’t told the provenance of the pork. Was it bought from a variety of markets, or one chain of supermarkets that might have one regional supplier? Was it organic v. conventional? Small-farm versus feedlot?
  • We can’t draw any broad conclusions from this. I am a poor biostatistician, but to me, this is purely a convenience sample. (If anyone disagrees with me, please weigh in.) In other words, it’s one data point. It says: There is MRSA in these packages of pork — which is an important piece of information — but it doesn’t say: 3% of all US pork contains MRSA.

Also, while the written version of the report that I linked above isn’t bad, overall, it contains one significant error. It says:

This drug-resistant bacteria is already responsible for more deaths in the US than AIDS. What makes MRSA so potentially dangerous is the bacteria can cause sickness just by touching it.

Well, not exactly. The concern with MRSA in meat is that, if you handle it without strict cleanliness, you might become colonized with the bacteria. That is not at all the same as developing a MRSA infection, much less the invasive MRSA the first sentence of that quote refers to. And yes, colonization can lead to infection. But to say that touching MRSA-contaminated meat will inevitably cause an invasive MRSA infection is alarmist.

I’m assuming the stations undertook this because it is sweeps month. (For those who have so far been spared the internals of TV news, “sweeps” are months — usually February, May, July and November — when stations’ audiences are measured to determine market rank and advertising rates. Because it is in the stations’ interest to attract as much audience as possible during those months, sweeps is usually when news stations run big investigative projects.) Interesting that they chose this topic. I think we can take this as an indicator — again, just one data point, but an interesting one — of emerging US concern over MRSA in meat.

Microbes in US meat, but no MRSA

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The ICAAC-IDSA meeting has ended, but there are still many abstracts that I have not been through. While I pore over them, though, an interesting paper has just been published that somewhat contradicts earlier research on the presence of MRSA in meat. (Earlier posts are here, here, here, here, here, here, here and here.)

The researchers, from the Warren Alpert Medical School of Brown University and Rhode Island Hospital, bought ground beef, boneless chicken breasts and pork chops from 10 stores in and around Providence. Two stores offered both conventional and “natural” choices, so they bought both, giving them 36 (=[10+2]x3) samples all told. They cultured for MRSA, vancomycin-resistant Enterococcus, extended-spectrum beta-lactamase producing Gram-negative bacteria and E. coli 0157:H7.

And they found… almost nothing. Only one samples grew a resistant microbe, the ESBL Gram-negative Serratia fonticola. A secnd level of testing, however, uncovered four samples carrying S. aureus — but all methicillin-sensitive, not MRSA.

So are we in the clear? Not necessarily. It is, as they say themselves, as small study, in which only a third of the samples were pork, though pigs are the animals most associated with MRSA via the strain ST398. And the presence of S. fonticola is troubling, because it not only causes disease directly (in animals and in humans), but also harbors a plasmid that can transfer resistance to other bacterial strains.

Nevertheless, it is a comforting reminder that, though MRSA has been found in meat, it has not been found everywhere. (Or at least, not in Providence.) Still, we shouldn’t let our personal vigilance lapse. The hypothetical danger from MRSA in meat is not that we’ll swallow it, but rather that we’ll be colonized if we handle the raw meat without being careful enough about kitchen hygiene. So keep raw meat away from other food, wash your cutting boards and counters, and (say it with me, now), wash your hands, wash your hands, wash your hands.

The cite is: Philip A. Chan, Sarah E. Wakeman, Adele Angelone and Leonard A. Mermel, Investigation of multi-drug resistant microbes in retail meats. Journal of Food, Agriculture & Environment, Vol.6 (3&4), July-October 2008.

ST 398 in New York City – via the Dominican Republic?

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Here’s a piece of MRSA news from the ICAAC meeting (see the post just below) that is intriguing enough to deserve its own post.

US and Caribbean researchers have found preliminary evidence of the staph strain ST 398, the animal-origin strain that has caused human illness in the Netherlands and has recently been found in Ontario and Iowa, in Manhattan. How it may have arrived: Via the Dominican Republic.

Th researchers (from Columbia University and Montefiore Medical Center in New York, three institutions in the Dominican Republic and one in Martinique) examine the influence of an “air bridge” — very frequent household travel — that is bringing MRSA and methicillin-sensitive staph back and forth between the Dominican Republic and the immigrant Dominican community at the north end of Manhattan. They compared 81 staph isolates from Dominican Republic residents and 636 from Manhattan residents and, among other findings, say that 6 Dominican strains and 13 Manhattan strains were ST398.

It is the first time ST398 has been found in Manhattan or in the Dominican Republic. (Most likely also the first time anyone has looked.)

The authors observe with some understatement:

Given the history of ST398’s rapid dissemination in the Netherlands, its history of methicillin-resistance and its ability to cause infections in both hospital and community, it will be important to monitor its prevalence in these new regions.

It is important to note that these ST398s were not MRSA — they were MSSA, methicillin-sensitive. However: Earlier this year, the Dutch researchers who have delineated the emergence of ST398 in Holland commented on the diversity of ST398 they have found on different pig farms and hypothesized that the resistance element has been acquired several different times by methicillin-sensitive staph. (van Duijkeren, E. et al. Vet Microbiol 2008 Jan 25; 126(4): 383-9.)

So it is possible to hypothesize that this strain arrived in Manhattan from the more rural Dominican Republic, though with the growth of hobby urban farming in NYC, one could also make the case that transmission went the other way. And it is also possible — I emphasize possible — that this could be a precursor to ST398 MRSA emerging in Manhattan. An interesting thought.

(This research is not online, because it is a poster presented at a medical meeting. For reference, the cite is: C. DuMortier, B. Taylor, J. E. Sanchez et al. “Evidence of S. aureus Transmission Between the USA and the Dominican Republic.” Poster C2-224. 48th ICAAC-46th IDSA, Washington DC, 24-28 Oct 2008.)

Closing the loop: meat, meat-eaters, health-care workers

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A posting on the international disease-alert mailing list ProMED led me to a scientific abstract presented at a European meeting this spring on the ST 398 MRSA strain. It adds another, quite unnerving piece to the emerging interplay of MRSA in pigs, humans who have close contact with pigs, humans who have contact only with pig meat, and health-care workers who treat those humans.

Brief precis: About a year ago, Dutch health authorities discovered that a patient who had come in for surgical debridement of a diabetic foot ulcer had an unrecognized MRSA strain in that ulcer. Subsequently, they discovered that four other patients and five health-care workers in the same institution were carrying the same strain. None of the patients reported any contacts with pigs (or calves, which have also been found to carry the strain). One of the health-care workers lived on a farm that raised pigs, but said that she had no contact with the animals in her daily life; nor did her partner.

The authors conclude:

While the source is not fully established it could be the HCW living on a pig farm. This outbreak makes clear that transmission on a larger scale can occur, even with NT-MRSA.

(Hat-tip to Helen Branswell of the Canadian Press for telling me about the ProMED report. And a note to loyal readers: The “MRSA in meat” story is being picked up by some US newspapers. Doesn’t it feel good to know you’ve been reading about the issue here for months? And if you’re a reader of Helen’s work, months more? Of course it does.)

New blog on animal health including MRSA

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Dr. J. Scott Weese of the Ontario Veterinary College (author of many important papers, discussed in many posts here, on MRSA in food and companion animals) has started a blog on animal-health issues. Here is a recent post on tracking down the source of a MRSA infection when there is a pet in the house.

The blog is called Worms and Germs and I’ve added it to the blogroll at right.

One more on MRSA in meat

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It turns out that European governments — in contrast to the United States — are taking very seriously the emergence of MRSA in food animals and its potential for transfer to humans. (For background, posts here, here, here and here.)

How seriously? They’re doing a sampling survey of pigs on farms across the European Union, at a cost of about $3 million in EC funds, with matching funds expected from each government.

The MRSA survey piggybacks (sorry) on a year-long survey of Salmonella incidence that the EC called for in September 2007. But in December, following publication of several significant papers about the ST 398 MRSA strain in pigs and pig farmers, the EC Directorate-General for Health and Consumer Protection pushed for an addition to the Salmonella study: a same-time sampling for the presence of MRSA strains in pig operations across 29 countries.

The sampling is taking place from January to December of this year, with results mandated by mid-2009, though individual country authorities may release data earlier if they choose. (In the wake of the finding of three ST 398 cases apparently caused by retail meat in the UK, the Soil Association has called on the British government to release whatever data it has ASAP. Before the EC decision, the UK government had refused to test its pigs; cf. these House of Lords minutes.)

Of note: The Soil Association is pressing the argument that ST 398 has developed in the setting of widespread use of antibiotics in food animals, and contends the strain’s arising in the Netherlands is especially alarming because they have some of the lowest animal-antibiotic use rates in the EC it illustrates the difficulties that even a society conscientious about antibiotic overuse can have keeping track of veterinary applications. The Netherlands has been successful limiting overuse in humans, but has found controlling veterinary use much more of a struggle. (Thanks to the Soil Association for correcting my misunderstanding!)