Thursday, December 6, 2007

The Cursa of the “Mursa”

A new germ scare has infected the American media. Five years ago it was the mysterious SARS, a couple years ago it was the civilization-threatening H5N1 Avian Flu and now it is the omnipresent and utterly malicious superbug known as MRSA (pronounced “Mursa”). MRSA (methicillin-resistant staphylococcus aureus) is everywhere; not just living in the upholstery of ICUs, the creases of the linens at grandma’s nursing home, the computer keyboards of your local emergency department; but also in the saunas of the downtown YMCA, the mats at the neighborhood yoga studio and the nostrils of about three-percent of the U.S. population.

Emergency Department personnel across the country are well-acquainted with MRSA as the profile of an infected patient has become classic: a previously healthy person with an unusual skin disturbance, usually in an unusual location. Maybe they call it a boil, a zit, or a spider bite, or maybe (if it is in an intimate location) it is referred to obliquely as “pain down there.” Most of these infections are easily treated with simple I&D (incision and drainage) and the patient can be sent home – sometimes with antibiotics, sometimes not. In some small, but not insignificant percentage of cases however, a MRSA infection attacks differently – in the lungs, the blood or the deep muscle layers. These potentially deadly aberrations are becoming more common and are the fuel for the recent frenzy of MRSA stories in the media. An October report from the CDC put the yearly MRSA death tally at 19,000 in the U.S. alone. This is indeed significant, especially when you consider that this number is twenty times the total human mortality from the H5N1 Flu and SARS combined.

About a month ago the mechanism for MRSA’s unusual method of infection was discovered. As it turns out, MRSA (and in particular the form of MRSA found outside of hospitals) plays a nasty trick on the body’s immune system. White blood cells from the immune system are drawn to the site of infection by a cluster of proteins (called phenol soluble modulins) that are released by MRSA, then these immune cells are destroyed by the same proteins – in a process that causes them to swell and explode – like a Ziploc bag of mashed potatoes left in the microwave too long. This provides an explanation for the strange phenomenon that emergency physicians like me have observed – MRSA skin infections that are miniature pus volcanoes, rising from otherwise pristine arms, legs, and nether regions and just waiting to erupt.

In the December 1st issue of The Economist I read about a newly emerging strain of MRSA, the so-called non-typable or NT-MRSA – which is not to be confused with other alphabet soup strains such as HA-MRSA (hospital-acquired MRSA) and CA-MRSA (community-acquired MRSA). NT-MRSA is an especially pig-nacious variation. Literally. NT-MRSA is a strain resistant to a class of drugs called tetracyclines that have up to now proven to be a relatively reliable antagonist for MRSA (86% successful treatment rate in a study out of Oakland, California). Tetracyclines along with other antibiotics, vaccines and insecticides are heavily used in pig farming to help fatten the swine (preventing infection means preventing loss of porkable meat). It is thought that this usage has caused the development of the NT-MRSA strain. A Dutch study cited by The Economist has found NT-MRSA in 39% of Dutch pigs and 81% of Dutch pig farms. A Canadian study found NT-MRSA in 20% of Ontario-area swine farmers. American hoggers also use antibiotics, so U.S. pig farms are surely not immune (if you doubt this, click on the link below to a 2006 Rolling Stone story about hog farms). Findings like this are too often described as “alarming” or “shocking,” but I don’t think the discovery of NT-MRSA fits in either of these categories (except perhaps, if you are a pig). Tetracyclines are not considered frontline drugs for treatment of MRSA – there are already other more effective options. But, it is never good to create antibiotic resistance, and especially if you do so not by helping people but by trying to make better bacon. Occasionally in my line of work, I will prescribe antibiotics to a patient even if I don’t think they need them. Usually, these patients have come to the ED with a clear agenda and will be disappointed, and perhaps angry, if that agenda is not fulfilled. In these situations I usually feel a little guilty, as I know I am contributing to the superbug problem. Now, I no longer have to think of myself as the villain – the pig farmers will do quite nicely.