Tag Archives: selection pressure

“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!