This is not good. A recent article in Emerging Infectious Diseases describes two separate cases of community-acquired ST398 MRSA–and neither case was associated with agriculture. Let me explain what this means and why this is really bad news.
MRSA–methicillin resistant Staphylococcus aureus–is a serious problem: in the U.S., it kills more people annually than AIDS. Typically, the therapy used to treat MRSA is vancomycin, and strains resistant to vancomycin can’t be treated on-label with any commercial antibiotics*. ST398 is a new clone of MRSA that is thought to be associated with agriculture–pigs in particular (hence, my designation of this as the ‘piggy MRSA’). In the Netherlands, in the course of a few years, it swept through pigs, and then colonized farmers, and recently has entered hospitals. In the U.S., it’s started to increase in pigs.
According to the article, two separate cases of community-acquired (i.e., they didn’t pick it up at a hospital) ST398 were observed, and they were very persistent. Neither patient had any animal contact, which means that this strain has jumped from the agricultural setting into the broader human community.
These strains also had PVL, which is a toxin that may increase the severity of disease**. What is very disturbing is that the strains were resistant to antibiotics other than methicillin (one was resistant to deoxycycline; the other was resistant to ciprofloxacin, erythromycin, and clindamycin). Not only are these strains multi-drug resistant, but the different resistance profiles suggests that ST398 is prevalent at a high enough frequency to have evolved divergent phenotypes (no mention is made if any of these resistances are plasmid-encoded).
*Skin infections can be treated with linezolid, but this therapy is not very effective against sepsis (bloodstream infections).
**The epidemiological evidence suggests PVL is nasty, but experimental studies in laboratory animals and cell culture yield mixed results.