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

Antimicrobial use in livestock can hurt humans

All IPs know that bacterial resistance to antimicrobials is increasing, but the problem isn’t just poor stewardship in humans – animal use is a culprit, too. The FDA recently released a draft guidance titled “The Judicious Use of Medically Important Antimicrobial Drugs in Food-Producing Animals,” which is intended to develop policy on animal antimicrobial use as it affects bacterial resistance and human health.

The guidance summarizes 15 key scientific reports going back to 1969 and then issues FDA’s non-binding recommendations. The reports study evidence that antimicrobial use in food-producing animals develops resistant bacteria, as well as evidence that bacteria is transmitted from the animals to humans. Almost every report concludes that using antimicrobials in food-producing animals poses a public health risk due to the development of bacterial resistance (the reports that do not reach the same conclusion say simply that there wasn’t enough evidence at the time to reach any conclusion at all).

Not all antimicrobial use in livestock is problematic – FDA does make the point that using antimicrobials is beneficial when it ensures animal health. However, sometimes antimicrobials are not used to prevent, treat, or control any disease, but to increase rate of weight gain or improve feed efficiency. Further, some of these antimicrobials are medically important for use in humans. As it is critically important that we maintain the effectiveness of antimicrobials for humans, FDA now calls non-therapeutic animal use “injudicious.” FDA recommends that non-therapeutic use of antimicrobials in animals be discontinued, and that all use should be overseen by veterinarians.

The guidance notes that FDA’s suggestions are non-binding, and requests comments from all interested parties.

You can read the guidance itself here: http://www.fda.gov/downloads/AnimalVeterinary/GuidanceComplianceEnforcement/GuidanceforIndustry/UCM216936.pdf

FAQ on the guidance here: http://www.fda.gov/AnimalVeterinary/GuidanceComplianceEnforcement/GuidanceforIndustry/ucm216939.htm