Maryn McKenna

Journalist and Author

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.

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

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.)