Maryn McKenna

Journalist and Author

Warning on ST398: Monitor this now

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Drawing your attention: I have a story up tonight at CIDRAP on a new paper by Dr. Jan Kluytmans, a Dutch physician and microbiologist and one of the lead researchers tracking “pig MRSA,” ST398. (All past stories on ST398 here.) It’s a review paper, which is to say that it summarizes key existing findings rather than presenting original research.

Still, it’s important reading because Kluytmans is one of the few scientists who have some history with this bug and understand how quickly and unpredictably it has spread across borders and oceans, from pigs to other livestock, to pig farmers and veterinarians, into health care workers and hospital patients who have no known livestock contact, and now into retail meat in Europe, Canada and the United States.

Take-away: A plea and warning for better surveillance, so that we can track not only the bug’s vast range, but also its evolution as it moves into new ecological niches — including humans who are buying that retail meat and possibly becoming colonized with it as they prep it for cooking in their home kitchens.

To honor fair use (and in hopes you’ll kindly click over to CIDRAP), I won’t quote much, but here’s the walk-off:

Because the novel strain has spread so widely and has already been identified as a cause of hospital outbreaks, it should not be allowed to spread further without surveillance, Kluytmans argues.”It is unlikely that this reservoir will be eradicated easily,” he writes. “Considering the potential implications of the reservoir in food production animals and the widespread presence in meat, the epidemiology of [MRSA] ST398 in humans needs to be monitored carefully.”

The cite is: Kluytmans JAJW. Methicillin-resistant Staphylococcus aureus in food products: cause for concern or case for complacency? Clin Microbiol Infect 2010 Jan;16(1):11-5. The abstract is here.

“Pig MRSA” in the EU – long-awaited survey

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It’s not very likely that people will be eating much pork today — OK, maybe some pancetta in the Brussels sprouts — and that’s good, because there’s lots of news today about MRSA in pigs.

(In fact, there’s a ton of news just this week. Make it stop.)

The European Food Safety Authority has published a long-awaited, European Union-wide survey looking for the presence of MRSA in pigs. Here’s the key points: Investigators found MRSA on 1 out of 4 farms where pigs were being raised and in 17 of the 24 EU states. (Two non-member states were included in the analysis.)

Strictly speaking, this is not a survey of MRSA in pigs; the study samples not the pigs themselves, but the dust in pig-raising sheds. The sites were 1,421 breeding farms and 3,176 farms where pig are raised to slaughter age. By far the most common strain was MRSA ST398, though other strains were detected, including some known human strains. The prevalence in various countries went from a low of 0 to as high as 46% of farms. (Highest, in descending order: Spain, Germany, Belgium, Italy, Portugal. The Netherlands, where St398 was first identified, had a prevalence of 12.8%. Countries reporting no MRSA: Bulgaria, Cyprus, Denmark, Estonia, Finland, Hungary, Ireland, Latvia. Lithuania, Luxembourg, Sweden, the United Kingdom, Norway and Switzerland.)

The report closes by recommending comprehensive monitoring of pigs for MRSA, as well as monitoring of poultry and cattle.

About the potential of ST398 crossing to humans, it has this to say:

In humans, colonisation with MRSA ST398 originating from pigs has been identified as an occupational health risk for farmers and veterinarians and their families. Although MRSA ST398 represents only a small proportion of the total number of reports of human MRSA infections in the EU… in some countries with a low prevalence of human MRSA infection, CC398 is a major contributor to the overall MRSA burden.
In most cases, colonisation with MRSA ST398 in humans is not associated with disease, although clinical cases associated with MRSA ST398 have been reported. MRSA ST398 can be introduced into hospitals via colonised farmers and other persons in a region with intensive pig farming. Therefore, MRSA ST398 may add substantially to the MRSA introduced in health care settings. However, it seems that the capacity for dissemination in humans (patient-to-patient transmission) of livestock-origin MRSA, in particular ST398, is lower as compared to hospital-associated MRSA).
… Food may be contaminated by MRSA (including ST398), however there is currently no evidence for increased risk of human colonisation or infection following contact or consumption of food contaminated by ST398 both in the community and in hospital.

Britain’s Soil Association, which pressed for the study to be done, has released a statement quoting the food safety agency warning that the testing method may have underestimated MRSA’s presence on farms, and warning that if ST398 is not yet in England, it is certainly soon to arrive. Germany’s Federal Institute for Risk Assessment also released a statement, admitting that ST398 in German pig stocks is “widespread.”

The report is here, executive summary here, and press release here. All well worth reading.

Restricting antibiotics in animals: Start by restricting access

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Constant readers, those of you who follow the pressing issue of MRSA in animals will know the work of J. Scott Weese, DVS, associate professor of pathobiology at the University of Guelph in Ontario and supervising author of many crucial papers on MRSA in food and companion animals, including the first finding of MRSA in pigs and pig farmers in North America.

You may not know that Weese and his postdoc Maureen Anderson publish an excellent blog on veterinary and zoonotic diseases called Worms and Germs (in the blogroll at right). This weekend they have an important post that deserves wider attention: Antibiotics: A Dose of Common Sense. In it, they propose that one way to reduce the overuse of drugs in food animals is to make animal antibiotics prescription-only. It’s worth taking the time to read it.

Those of you in the cities may not know this, but out here in the Great Flyover, antibiotics for veterinary use are surprisingly easy to buy (as I discovered when I stumbled into a farm-related store in search of a Carhartt jacket against the Minnesota winter). They’re not even over-the-counter — they’re on the shelf, or stacked on the floor with the implements and feed, or blended into the feed itself. And as Weese points out in this post, they are also available without prescription over the Internet (as human antibiotics are too).

It’s a potentially controversial proposal: I don’t think I have any farming readers, but I would imagine their response would start with an objection to the extra cost of hiring a veterinarian to assess whatever situation might require the drugs. And since most farmers (NB: not the overarching ag-biz companies, but the farmers themselves) exist on razor-thin economic margins, they would have a point. But as we know from the excellent work of Extending the Cure and the Center for a Livable Future, unnecessary antibiotic use comes with a cost as well — one that is borne by all of us when antimicrobial resistance prevents antibiotics from working.

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.

More on MRSA and the new flu

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Constant readers, I admit it: I am a bad blogger. The wave of news on the novel H1N1 (AKA the Virus Formerly Known as Swine) has been just overwhelming. Apologies for disappearing.

Out of the crashing surf, though, I picked up an interesting tidbit that speaks to our concerns about MRSA. Here’s some background: If you have been following the swine flu story, you’ll have noticed that one of the puzzles has been why the Mexican experience has been so different from the United States or from the other countries where this flu has appeared briefly. (North America so appears to be the only area in which there is sustained transmission.) Among the hypotheses:

  • There is a difference in the medical care that victims are receiving.
  • There is a statistical artifact: The serious cases are a tiny percentage of the mild cases, and the US has not seen enough cases to, probabilistically, experience significant serious cases yet.
  • Or, corollary to the above: Mexico has many more cases than its surveillance systems have been able to count, and that is why we have seen that (unknown but presumably tiny) percentage that become serious cases appear there but nowhere else.

(For more on this, here’s a CNN story from a few days ago, quoting me and people much more distinguished than me.)

But a commentary by a global-health expert raises another hypothesis, one that brings this outbreak around to our concerns: the possibility that the serious flu cases in Mexico are being complicated by secondary pneumonia caused by MRSA or other bacteria.

We’ve talked about this issue before (see this post about the importance of MRSA in a flu pandemic and this paper by, among others, Dr. Anthony Fauci, director of NIAID, and Jeff Taubenberger, PhD, co-discoverer of the virus of the 1918 flu). MRSA pneumonia secondary to flu infection is the etiology of the necrotizing pneumonia cases that kill children very quickly, and is the reason why I keep haranguing you regarding flu shots.

Is bacterial pneumonia playing a role in the current epidemic? It’s too soon to tell; there is not sufficient clinical data. But it is an interesting speculation and one that we should keep in mind as this goes forward.

For a moment, a different pathogen: swine flu

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Constant readers, some of you know that I have a long history of covering pandemic flu (I wrote the first story in the US media about avian flu back in 1997, and covered pandemic preparations for years). I’ve had that somewhat on the back burner while I worked on this MRSA project and handled some personal family matters, but with the book manuscript almost completed and the family stuff ending, looks like I will be covering flu again.

For now, let me direct you to some resources:

  • My colleagues at the news site of the Center for Infectious Disease Research and Policy are doing yeoman work with very few resources. Some of you many know CIDRAP as home base of Michael Osterholm, PhD, advisor to several administrations on pandemics and disasters and pandemic-flu interviewee on Oprah. The CIDRAP site includes a series I wrote about 18 months ago now that explains why it will be so hard to achieve a flu vaccine in time for the start of a pandemic.
  • Helen Branswell of the Canadian Press is the most connected flu reporter on the planet; because she is at a wire service, there is no one page to send you to, but Google her name, or follow her on Twitter @diseasegeek.
  • My fellow global-health reporter Christine Gorman, formerly of TIME Magazine, has put up a thoughtful post with many links on her blog Global Health Report.
  • There are seriously good flu blogs (also in the blogroll) at Effect Measure, H5N1, Avian Flu Diary, Scott McPherson’s Journal, A Pandemic Chronicle and the indefatigable preparation-conscious groups bloggers at ZoneGrippeAviare (in French and English).
  • University of Iowa epidemiologist and zoonotic-disease expert Tara Smith, PhD., is blogging thoughtfully at Aetiology.
  • Several years ago I helped conduct a conference at Nieman House at Harvard, the home base of the Nieman Foundation and fellowships, on understanding and getting ready to cover pandemic flu. The materials are here.

That’s all for now. More soon, I expect on both MRSA and flu.

Appearing today on The Ethicurean

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Constant readers, I want to let you know that the terrific food policy blog The Ethicurean (motto: “Chew the right thing“) very kindly had me over to do a Q&A on MRSA in meat. Please take a look and let them have some clicks: They are smart people thoughtfully elucidating a difficult subject, and worth following.

(And I would say that even if they hadn’t called me the “Superbug supersource,” honest.)

More MRSA in pigs, in Portugal

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A brand-new report, in a letter to the International Journal of Antimicrobial Agents, indicates that ST398 “pig MRSA” has been found in Portugal for the first time.

Constanca Pomba and colleagues from the Technical University of Lisbon swabbed and cultured the noses of pigs and veterinarians on two pig farms in different regions of Portugal, and also checked the air at both farms.

What they found:

  • On Farm A: All pigs and the veterinarian positive for ST398, the pig-origin strain that has been found so far in Iowa, Ontario, the Netherlands, France, Denmark, Germany and Austria and has, depending on the country, caused human disease and/been found on retail meat. The veterinarian was transiently colonized, which is to say that he was not carrying the bug long-term.
  • On Farm B: All pigs — but neither of two veterinarians — positive for a different MRSA strain, CC (or ST) 30. This is very interesting, because CC30 is usually a drug-sensitive strain (MSSA, methicillin-sensitive S. aureus), and has been found in pigs primarily in Denmark and France. In Portugal, it is a human MSSA hospital-infection strain.

Strains from both farms were resistant to tetracycline; this is turning out to be a great marker for these strains having emerged due to antibiotic pressure in animals, because tetracycline is very commonly used in pigs. but not much used for MRSA in humans. The strains have the genes tetK and tetM, so they are resistant not just to tetracycline itself, but to the whole class of tetracyclines including doxycycline and minocycline. The Farm B strains also carried the gene ermC, which encodes resistance to erythromycin.

So what does this tell us?

  • First, that (once again), every time people look for ST398, they find it; it is now a very widely distributed colonizing bug in pigs, and is repeatedly spreading to humans. What we don’t know, because all these studies are so new, is whether ST398 is actively expanding its range, or has been present in all these countries for a while. We have been anticipating its presence or spread (take your pick at this point) through the European Union because of open cross-border movement of food animals, meat, and agriculture and health care workers.
  • And second, it should tell us that it is really past time to start looking for this more systematically. Every finding of ST398 that we have (long archive of posts here) is due to an academic research team who decided to look for the bug. None of the findings, to date, have come from any national surveillance system. (NB: Except for the first human colonizations in the Netherlands, which were found as a result of the national “search and destroy” rules in hospitals.)

Of note, the European Union is running a study now that is supposed to report ST398 prevalence at any moment (as they have been saying since 2007). It is not expected to be comprehensive, since it was piggy-backed onto another study, but it is something. The US government has not been so enterprising.

The cite is: Pomba, C. et al. First description of meticillin-resistant Staphylococcus aureus (MRSA) CC30 and CC398 from swine in Portugal. Intl J Antimicrob Agents (2009), doi: 10.1016/j.ijantimicag.2009.02.019

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]