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

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]

Maryn

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