Tag Archives: MDRO rates

“Pressure Control”

Controlling the volume of Multi-Drug Resistant Organisms (MDROs) within an institution is just as much about controlling the selection pressure as it is about controlling the transmission. (Don’t tell the Infection Control nurses that, but it is absolutely true!)

In my opinion the selection pressure control is actually the more important of the two. There will always be transmission despite our best efforts…

For those who are involved with antimicrobial stewardship and Infection Control, you will be aware that we are very good at monitoring our MRSA/ESBL/VRE/CRE rates etc., etc. We look at pretty graphs illustrating this every month at our committee meetings.

However we are not so good at monitoring our selection pressure. By this I mean that we should be taking 5 or 6 key broad spectrum antibiotics (e.g. meropenem, piperacillin tazobactam, tigecycline, ciprofloxacin, etc.) and monitoring objectively their usage on a month by month or quarter by quarter basis.

Most of us have guidelines on the clinical indications for the appropriate use of these key broad spectrum antibiotics. Some institutions go further and require endorsement by an Infection Specialist before their use. However very few of us actually monitor this usage in an objective fashion and then present these surveillance findings at monthly infection control/stewardship meetings.

I have come across institutions with sophisticated antimicrobial stewardship guidelines and well established anti-microbial stewardship committees. Yet the same institutions can have ITUs where more than half the patients passing through the door will get a carbapenem. An MDRO arriving in such a unit simply thinks all his birthdays have come at once, and will make himself at home in no time at all…

That is selection pressure!

If I was a CEO of a hospital that had a problem with endemic Carbapenem Resistant Enterobacteraciae (CRE), I would want to know exactly how much of each of the key broad spectrum antibiotics were being used in the hospital, and then whereabouts they were being used, by whom, and why.

For me, the antimicrobial pharmacist is one of the key members of any infection control team. You can write as many guidelines as you want, but unless you have a firm handle on exactly how much selection pressure you have in your hospital, and how that pressure is trending over time, you may find yourself sitting on an MDRO time bomb.


Do bacteria have birthdays? Not sure about that!

MDRO Screening: Part 1: “Made to Measure”

I am talking here about Multi-Drug Resistant Organisms in the bacterial sense, ie MRSA, ESBLs, VRE etc.

The first thing to say is that in New Zealand we don’t see that many of them, certainly compared with other countries in the world. Click here for more about this.

But what I want to focus on here is the measurement of MDRO rates. There are two main ways to measure these rates.

  • 1) Crude Rates: The total number of MDRO isolates per population. e.g number of MRSA isolates per 100,000 population. This is the type of measurement preferred by reference laboratories as they often only receive the resistant isolates, not the susceptible ones…. However this type of rate varies widely depending on how much screening is done at any one institution. The more MDROs are looked for, the more that will be found. The amount of MDRO screening performed in New Zealand varies dramatically from one hospital to another dependent on contractual and other factors.
  • 2) As a percentage of total isolates. The MDRO rate can also be measured as a percentage of the total number of bacterial isolates, both susceptible and resistant. e.g The MRSA percentage rate is calculated by calculating the number of MRSA isolates as a percentage of the total Staphylococcus aureus isolates (both methicillin susceptible and resistant). A further example is the percentage of ESBL producing E.coli as a percentage of total E.coli.

I prefer the latter method. I think it is more comparable across areas and it also allows better comparison of rates over time. The Crude MDRO rate measurement is too biased by the amount of testing done and is also susceptible to population fluctuation.

I am not saying that the percentage method is perfect. Like all these things it is susceptible to bias also…..

Currently in our laboratories (NZ): (2012)

  • 10% of our total Staph aureus isolates are methicillin resistant (MRSA)
  • 1% of our E.coli isolates are ESBL producing.
  • 11% of our K. pneumoniae isolates are ESBL producing.

When I return to work in Europe it will interesting to compare the percentage rates with what I am currently used to and speculate as to the differences.