MRSA infections down, but new threat on the horizon

A study just published in The Journal of the American Medical Association (JAMA) shows that the incidence of hospital-onset methicillin-resistant staphylococcus aureus (MRSA) infection decreased by 28% from 2005 to 2008.  The measurements, taken from 9 major metropolitan areas across the country, also show that MRSA rates for healthcare-associated community-onset infections decreased 17% over the same time period. 

The study’s authors, Kallen et al., are unable to say why the rates decreased, but mention a couple possible factors.  The first possibility is the widespread implementation of MRSA prevention practices.  Kallen et al. note that “the fact that the observed reductions were greater among hospital-onset infections than healthcare–associated community-onset infections suggests that prevention practices in acute care settings contributed” to the decrease in MRSA infection rates.  Another potential factor is a change in the strains associated with MRSA infections, but the authors state that there weren’t changes in MRSA strain composition during that time period, so this is unlikely to be a valid explanation. 

Immediately on the heels of this good news comes a study published in The Lancet Infectious Diseases today, which details how a new bacterial gene might cause worldwide health problems.

NDM-1, which stands for New Dheli metallo-β-lactamase 1, makes bacteria highly resistant to many classes of antibiotics, including the carbapenems.  Unfortunately, the gene has been determined to be readily transmitted and also highly adaptable.  As bacteria that contains NDM-1 encounters bacteria that doesn’t, NDM-1 could insinuate itself into the new bacteria, thus creating a larger resistant population.  The problem is particularly worrying because there is not a single antibiotic in the discovery and production process that is effective against NDM-1-containing bacteria – and because NDM-1 is highly adaptable, it could potentially change itself to resist any drugs that are developed. 

In addition to this already grim news, most of the isolates taken from India were from community-acquired infections, which implies that bacteria with the NDM-1 gene are already pervasive.  The NDM-1 gene has also already spread to the UK and Sweden – and some of the UK patients had recently traveled to India for medical treatments. 

We’re left with a good news/bad news scenario: just as we are starting to see MRSA infection rates fall, we learn that NDM-1-containing bacteria is expected to spread around the globe.

JAMA article: http://jama.ama-assn.org/cgi/content/full/304/6/641
Lancet article: http://www.thelancet.com/journals/laninf/article/PIIS1473-3099%2810%2970143-2/fulltext