Some Interesting Staphylococcus aureus Factoids

Or maybe terrifying is a better word. I just returned from the Network on Antimicrobial Resistance in Staphylococcus aureus meeting, where I learned some very interesting things about S. aureus (since I'm going to refer to MRSA, methicillin resistant S. aureus repeatedly, go check this link if you want to know more about MRSA):

1) 43% of all skin infections in the U.S. are the result of one strain of MRSA. Not 43% of staphylococcal infections. All skin infections.

2) According to the NHANES study, the number of people who carry S. aureus asymptomatically (in other words, it lives up your nose and isn't making you sick) dropped from 34% in 2001-2002 to 28% in 2003-2004. That's the good news...

3)...the bad news is that the percentage of people who carry MRSA asymptomatically increased from 0.8% to 1.5% (I've seen the experimental design; these changes aren't statistical wobble but real changes based on good sampling and large population sizes).

4) The MRSA and MSSA clones (a 'clone' is a group of genetically related strains) that show up in clinical settings and cause disease are actually quite rare in the commensal S. aureus populations.

5) Over the last several years, there has been a huge shift in MRSA. Most MRSA used to be hospital-acquired (the infection began after 48 hours had be spent in the hospital; 'HA-MRSA'). Now, roughly 75% of MRSA are either community-acquired (the patient enters the hospital infected and onset occurs before 24 hours has been spent in the hospital; 'CA-MRSA') or hospital-associated community onset MRSA (onset occurs between 24-48 hours of hospital entry; 'HACO-MRSA'). What interesting is that these HACO-MRSA, while 'community acquired', are associated with people who spend lots of time in medical facilities or have other risk factors (e.g., surgery within the last month). I suspect that the HACO-MRSA strains are adapted to high antibiotic environments (e.g., frequent hospital stays, nursing homes, etc.), even though they often resemble CA-MRSA in other ways.

6) Nobody has any idea whether PVL toxins increase MRSA virulence, decrease MRSA virulence, or have no effect at all (three researchers, three different conclusions). I think all we can say is that we are far better at killing mice than humans with MRSA. Of course, if you were exposed to a quart of dense MRSA culture, you would probably be dead too....


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I've heard that Canada has similar MRSA problems, but I don't know if the European Community is dealing with this better, or worse, than we are. Does anybody know?

Perhaps they need to establish a medical community related classification (MCR-MRSA). A very good friend almost died after picking up an infection while getting a dental implant.

MRSA is definitely and issue in Europe. I worked at the microbiology department at a hospital in Germany for a year or so, and the majority of wound infections were MRSA. MSSA was a rarity, and it's obviously community acquired. They do monitoring, and keep statistics of cases, just like anybody else, but I can't say that they're doing anything special to combat it. There's a lot of research going on about it over here though. Germany's already famous for microbiology research, and they're still going strong.

According to this Slate article, European and Canadian hospitals are testing all high-risk patients (including anyone from the U.S.) for MRSA when they come in and quarantining those who test positive.

I think the community acquired MRSA (CA-MRSA) definition is getting a little useless, since these strains have inflitrated healthcare facilities. Plus, not all clinically-defined CA-MRSA is of the nasty clone... why don't we refer to the PFGE type (USA300 or 400) or even ST types?


It really depends on the country. Denmark and the Netherlands have very low MRSA rates (<2%). Other European countries are worse than the U.S.


I agree; the CA/HA distinction is started to breakdown, in large part due to the epidemic spread of the USA300 clone. It appears that much of the CA-MRSA is also USA300, although I think that's biased (the less serious MRSA infections aren't typed, so I think the USA300 strains are overrepresented). FYI, the skin strain I was taking about is USA300-0014 (or maybe 0114; I can't remember).

Regarding nastiness, USA100 & USA400 strains can still pack a wollop.

I keep reading about MRSA in hospitals and nursing homes but has anyone, anywhere, considered infection rates in teachers? I am a preschool teacher and have just been diagnosed with a MRSA.
Any thoughts?

By Katherine (not verified) on 09 Mar 2007 #permalink

Hospitals? Nursing homes? My own little run-in with MRSA was in no way connected to either: it was the result of falling down on a rainy night in Portland last year and skinning my knee (I was even sober!;)). Voila! Two weeks later I was in the hospital having my leg opened up and bursa scraped, under the drip. Since I lead a normally hygienic lifestyle and washed the scratch and applied iodine to it upon getting home, the provenance of said bug is still a mystery to me (puddles in the street? or was I asymptomatic myself?). But I am much more paranoid of minor wounds nowadays. It's all a part of growing up, I suppose...;)

To answer Roy's question:

Britain has serious MRSA problems. I get the impression that more is being done there to make people aware of the problem than in the US. For example, my parents have been told to only have essential surgery. Additionally, when I visited my Dad in hospital eighteen months ago, there were hand wash stations by the ward doors. In the restrooms, there were even charts showing you how to clean your hands properly.

I didn't notice any of this when I was in hospital in the US about fifteen months ago or since when I've been back for tests and check ups.

Why actually are american hospitals so nonchalant about mrsa? They need to spend more on antibiotics than other countries due to that. Britain used to have low mrsa-rates but then Thatcher came into power. :-(

I must say first of all it is nice to see a blog like this, and i am in the same boat. I invite you to read my story. There is a product that i have found that does not CURE MRSA but can help stop the symptoms. Know fact recently while i was at my doctors office, he told me that there is a cure but it cost thousands of dollars. Not alot of insurance companies accept this bill, but there maybe hope. if you suffering with MRSA symptoms, check my blog out. There is a little hope out there.

I now have a Non-profit Organization called VM MRSA Group Foundation, that is dedicated to help educate, support and guide the MRSA Community.

God Bless,
Dawncarla DeLaPaz