Maryn McKenna

Journalist and Author

Update: The French case — not MRSA but so interesting

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I’m flattered to have as a regular reader Dr. Peter Davies, a professor of swine health and production in the University of Minnesota’s Department of Veterinary Population Medicine. (Disclosure: I worked part-time at U Minn from mid-2006 to mid-2010, but in a different school.) In a comment on my previous post, he points out — perils of reading on a smartphone — an important point where I erred: The staph strain involved in the death of the French 14-year-old was not MRSA, but MSSA, drug-sensitive staph, that had picked up a resistance factor.

Unpacking that a bit: At a minimum, MRSA is resistant to all beta-lactam antibiotics — penicillin, the semi-synthetic penicillins (including methicillin, what the M in MRSA stands for), several generations of cephalosporins, monobactams, and carbapenems. It is also separately, but variably, resistant to macrolides (such as erythromycin), lincosamides (clindamycin), aminoglycosides (gentamicin), fluoroquinolones (ciprofloxacin) and tetracycline.

Livestock-associated MRSA, known as ST398 for its performance on a particular test (multi-locus sequence typing) was first identified as having a tie to pig-farming because it was also resistant to tetracycline, which was being given to the pigs on the farms where the first human carriers worked. (Hence its jocular name, “pig MRSA,” though it’s since been found in other animals.)

The ST398 strain involved in the French girl’s death does not have that broad array of resistance. Chiefly, it was not resistant to beta-lactams, and so can’t be considered MRSA. On analysis, it was resistant to the macrolides, of which the best-known are erythromycin and azithromycin (Zithromax or Z-Pak). Here’s something else intriguing: On another test (spa typing), the ST398 strain in the French girl was one known as t571; the ST398 that has spread from pigs to humans in the European Union, and subsequently to Canada and the United States, is usually t034.

Here’s why this is all so interesting: MSSA ST398 t571 was reported just a few years ago in New York City, in a Bronx community that has close ties to the Dominican Republic, and also in the towns in the Dominican Republic where those Bronx residents come from and visit. (Here’s my initial post on that finding from a medical meeting, and subsequent post when the paper was published.) In that case, the ST398 was fully drug-sensitive — and there was no visible link to pigs, though the authors speculated that livestock, perhaps poultry, might be playing a role on either side of the “air bridge” connecting the two communities.

In the paper (Bhat, Dumortier, Taylor et al., EID 2009, DOI: 10.3201/eid1502.080609), the authors expressed concern that, given staph’s promiscuous ability to acquire resistance — and the fact that ST398 is not regularly surveilled for —  the ST398 in New York could become an undetected resistant strain:

Given ST398’s history of rapid dissemination in the Netherlands, its potential for the acquisition of methicillin resistance, and its ability to cause infections in both community and hospital settings, monitoring the prevalence of this strain in northern Manhattan and the Dominican Republic will be important to understand more about its virulence and its ability to spread in these communities.

 And now it appears it has become resistant — but in France, not New York City or the Dominican Republic, and to macrolides, not  beta-lactams. It’s one more reminder of staph’s genius at acquiring genetic defenses, and of how our lack of attention to its mutability and spread continues to allow it to take us by surprise.

One surgical infection with MRSA: $61,000

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From a multi-state, public-private research team — Duke University, Wayne State University, and the Durham, NC VA — comes a precise and alarming calculation of MRSA’s costs in hospitals: For one post-surgery infection, $61,681.

The group compared the course, costs and final outcome of three matched groups of patients from one tertiary-care center and six community hospitals in one infection-control network run by Duke. The three groups were: patients with a MRSA surgical-site infection; patients with a surgical-site infection (SSI) due to MSSA, drug-sensitive staph; and surgery patients who did not experience infections, matched to the other two groups by hospital, type of procedure, and year when the procedure took place. (This same cohort has been described in an earlier prospective study that looked at risks for MRSA SSIs.) Altogether, there were 150 patients with MRSA SSIs, 128 with MSSA SSIs, and 231 uninfected surgery patients to serve as controls.

Here’s what they found. Patients with post-surgical MRSA infections:

  • stayed in the hospital 23 days longer
  • incurred an average extra cost of $61,681
  • were more likely to be readmitted to the hospital within 90 days
  • were more likely to die before 90 days had passed.

The authors write:

Our study represents the largest study to date of outcomes due to SSI due to MRSA. Our findings confirm that SSIs due to MRSA lead to significant patient suffering and provide quantitative estimates of the staggering costs of these infections. SSI due to MRSA led to a 7-fold increased risk of death, a 35-fold increased risk of hospital readmission, more than 3 weeks of additional hospitalization, and more than $60,000 of additional charges compared to uninfected controls.

For just the patients in this study, the excess costs (across 7 hospitals) totalled $19 million.

This is a highly useful study on several axes. First, remarkably, there has not been agreement over whether and how much of a problem MRSA poses in post-surgical settings, particularly when compared to drug-sensitive staph. This study provides careful, thoughtful, well-documented proof that combating MRSA infection is worthwhile. (NB, MRSA infections did not increase the risk of death relative to MSSA infections, which should remind us both of the often-forgotten virulence of MSSA, and also that MRSA’s perils can lie in extended illness and disability as much or more as in early death.) Second, by putting a very specific number on the cost of a post-surgical MRSA infection, it gives healthcare administrators a benchmark against which they can judge the cost of a prevention program. We’ve all heard complaints that prevention programs can be costly and their benefit is hard to measure in a bottom-line way. With this very specific number, that complaint should no longer be valid.

There’s a final point that is implied in the paper but not called out, so let me call it out on the authors’ behalf. These results are very likely an under-estimate of MRSA’s costs. That’s because, first, the specific procedures the patients underwent were cardiothoracic and orthopedic; those are not the surgical procedures most likely to be followed by a MRSA infection. And second, data collection for this study ceased in 2003, about a year after the first emergence of USA300 and several years before that very successful community strain began its current move into hospitals. However much MRSA was extant in 2003, there is more now.

The cite is: Anderson DJ, Kaye KS, Chen LF, Schmader KE, Choi Y, et al. 2009 Clinical and Financial Outcomes Due to Methicillin Resistant Staphylococcus aureus Surgical Site Infection: A Multi-Center Matched Outcomes Study. PLoS ONE 4(12): e8305. doi:10.1371/journal.pone.0008305

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

Child deaths from flu + MRSA, again

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Folks, I am close to manuscript deadline and so keep disappearing down the rabbit hole; forgive me if I don’t post as regularly as usual, I’ll be back as soon as I can.

I wanted to point out the announcement by the Centers for Disease Control late Friday that we are starting to see children dying from MRSA this flu season. (The architecture of the linked page is unfortunately way clumsy; at the link, scroll down to the subhead “Influenza-Associated Pediatric Mortality.”)

Since September 28, 2008, CDC has received nine reports of influenza-associated pediatric deaths that occurred during the current season.
Bacterial coinfections were confirmed in six (66.7%) of the nine children; Staphylococcus aureus was identified in four (66.7%) of the six children. Two of the S. aureus isolates were sensitive to methicillin and two were methicillin resistant. All six children with bacterial coinfections were five years of age or older.

We’ve talked before (here, here and here, among other posts) among the emerging understanding of the particular danger that MRSA poses during flu season, when (it is hypothesized) inflammation from flu infection makes the lungs more vulnerable to secondary bacterial infection.

(For those paying attention to the hospital v. community MRSA debate, this is a community-associated infection, not a hospital one.)

This current CDC bulletin underlines, just in case we have forgotten, that drug-sensitive S. aureus (MSSA) can be a serious foe as well. Let’s remember, resistance makes MRSA less treatable than MSSA, but it does not change its virulence; MSSA by itself can be a very serious foe. Yes, there are other changes in some strains, especially the community ones, that do appear to increase virulence, but the original MSSA strain is nothing to trifle with.

Also, here’s an important addition to this unfolding story: My colleagues at the Center for Infectious Disease Research and Policy are keeping track of kid deaths around the country. According to them, these CDC numbers are already out of date; they have uncovered more that the CDC has not yet posted, but may take note of in future weekly updates.

“Pig MRSA” in New York City – via the Dominican Republic?

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Folks: Back in October, I broke the news for you of an intriguing poster presentation at the ICAAC meeting. It revealed the discovery of ST 398, the anomalous staph strain found in pigs, pig farmers and health care workers in Europe, in residents of a Dominican-immigrant neighborhood in northern Manhattan, and also in the Dominican Republic.

Because there is so much traffic back and forth between those neighborhoods, the authors theorized that people are providing an “air bridge” for the bacterium — though they were unable to say whether the bug is moving from the Dominican Republic to the United States, or vice versa.

I was unable to link to that presentation at the time, because it was a meeting poster – yes, literally a poster, the authors stand by it to discuss it with anyone who wanders by. However, now it has been published as a paper, in the CDC journal Emerging Infectious Diseases; and because it is a CDC journal, the full text is available free online here.

Just to underline, despite my headline above, the strain found in NYC was not MRSA: It actually is MSSA, drug-sensitive staph. The ST 398 found in Europe, Canada and the American Midwest is MRSA. The authors hypothesize that the NYC strain is at risk of becoming MRSA also.

To see the multiple posts in this blog about MRSA ST 398 and other strains in the food chain, food animals, and pets, go to the labels under the time stamp on this post, and click “animals” or “food.”

The cite for the paper is: Bhat M, Dumortier C, Taylor B, Miller M, Vasquez G, Yunen J, et al. Staphylococcus aureus ST398, New York City and Dominican Republic. Emerg Infect Dis. 2009 Feb; [Epub ahead of print]

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.

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.)