Bacterial Fitness and Antimicrobial Resistance

I just posted about how little we understand the rise and fall of MRSA. As a follow-on, read this recently published work from Denmark—which investigates the relative “fitness” of different S. aureus isolates within clonal complex 8 (using older terminology, phage type 83A). As might be expected, the more resistant strains were relatively less “fit”, and in the absence of antimicrobials were "out-competed" by the more susceptible strains. The authors suggest that one explanation for the waning of Denmark’s MRSA epidemic was the bacterial fitness cost of maintaining resistance in the absence of antimicrobial pressure.

We often discuss the transmission and spread of resistant bacteria on this blog, but we rarely discuss the downside, from the bacteria’s standpoint, of maintaining multiple drug-resistance mechanisms. This concept is quite old, and fairly intuitive. Wearing 30 pounds of body armor and lugging an 80-pound rucksack might favor the survival of a soldier in combat, but if I wore this gear for my daily walk to work (through non-hostile territory), I might not make it to my office. See this Nature Blog post from 2010 for a great general discussion of this topic.

Illustration by Don Smith

Time to pull out the dumb list

The fomite train at the Binscombe Doctor Blog

It's been awhile since we've visited the dumb list, a collection of really dumb things hospitals have done in the name of infection prevention. Here's the latest:

• Banning a wooden train from a general pediatric surgery clinic that does not care for immunocompromised children

Other banned items and activities from our archives:

• Christmas decorations
• Aquariums
• Flowers
• Sitting on the hospital bed
• Reducing hospital visiting hours from 4 hours to 3.5 hours
• Magazines in waiting rooms

Hat tip to Eli. 

Delayed Bed Assignment Due to Contact Precautions

Many of us have concerns about contact precautions. The benefits associated with reduced transmission must be balanced against potential side-effects like fewer or shorter visits from their doctors or nurses.  Another issue with isolated patients is that they may be harder to place in long-term care or even acute-care facilities since it is often hard to find single-bedded rooms and time consuming to cohort patients.

With that in mind, investigators at MGH in Boston designed and completed a survey of 1074 patient access managers (the people in charge of bed assignments) to determine the impact that contact precautions has on patient bed placement. They found that MRSA+ patients required a median of 29 more minutes for inpatient bed assignment and VRE+ patients required an additional 28 minutes. Limitations of the study: 22% response rate and self-reported data.

Source: Shenoy ES et al. ICHE 2012

The mystery of the Staphylococcus in retreat

Evidence keeps accumulating that Staphylococcus aureus disease, for whatever reason(s), is declining in incidence. The latest massive study to illustrate this trend is courtesy of the U.S. Military Health System and is published this week in JAMA. Using their integrated electronic medical record, military epidemiologists demonstrate that both community- and hospital-onset S. aureus bloodstream infections (MRSA and MSSA) declined in incidence between 2005-2010, and that the proportion of S. aureus skin/soft tissue infections due to MRSA declined beginning in 2007. While it might not be generalizable, the Military Health System is very large, encompassing active duty military, retirees, reservists and their families, and this study included over 56 million person-years of observation.

One strength of this study is that it shows not only healthcare-associated but also community S. aureus disease to be declining, a decline that is difficult to attribute to hospital-focused interventions. The reports now from NHSN, the Active Bacterial Core Surveillance program, the United Kingdom, the EARSS system, and now the military all speak to our ignorance of the complex interplay between S. aureus and its human reservoir. Successive long cycles of waxing and waning epidemic spread have been, and will be, the rule. 

For a nice example, check out this study from Oxfordshire hospitals demonstrating how their MRSA incidence began to drop well in advance of intensified infection control interventions, and how this drop coincided with the rise and fall of two competing strain types.

Image from Planet Science

Not reading the blog on Independence Day? You're missing this...

From Jennifer Gardy - an IDWeek Speaker and Microbiologist

Happy Fourth of July - The Infected US President

Nothing is more American than the Presidency. I have no idea why that is or if it's even true, but it sounds good. Over at The History of Vaccines blog, Alexandra Linn has a nice post describing the infectious diseases that have plagued the US Presidents and their families.

From the nine deadly diseases that plagued George Washington to FDR's polio, it's clear that infectious diseases don't always spare the connected and wealthy - a true democracy. Of course, nothing was sadder than Old Tippecanoe's (William Henry Harrison) death by pneumonia only one month after his inauguration speech. He was the first President to die in office.

Happy Canada Day 2012!

A few myths about the Canadian system can be found here. A couple salient facts are found in the graph from the post below—longer life expectancy for half the per-capita investment. It isn’t just Canada, either. The U.S. is super-terrific at spending tons of money to achieve slightly worse outcomes than the rest of the industrialized world.