Sunday, December 2, 2012

The ghosts of the "prior room occupant"

"Well, you know, Doc, when something happens, [it] can leave a trace of itself behind. Say like, if someone burns toast. Well, maybe things that happen leave other kinds of traces behind. Not things that anyone can notice, but things that people who "shine" can see….I think a lot of things happened right here in this particular hotel over the years. And not all of 'em was good."

-From the movie The Shining, 1980 

I’m reviewing papers for a talk I’m preparing on “control of multiple drug resistant gram negative rods (MDR-GNRs)”. So I’m looking again at a set of studies that always scare me (even more than a Stephen King novel)—those that demonstrate that a variety of bad bugs (C. difficile, MRSA, VRE, and MDR-GNRs) can be “left behind” after a patient is discharged, poised to colonize or infect the next occupant of that hospital room. It is a scandalous indictment of current hospital disinfection practices that patients must be haunted by the pathogens of the previous occupant of their hospital bed! 

There are still some practical (and financial) hurdles that must be overcome before new disinfection technologies (UV light, H2O2 vapor, antimicrobial surfaces, etc.) become standard of care. In the long run, though, I think that’s where the future lies—excellence in cleaning will remain important (organic debris will always require removal), but for microbial eradication in the environment, these technologies are going to replace our existing, more rudimentary approaches.


  1. These studies scare me for a somewhat different reason. If memory serves me, none really controlled for colonization pressure on the unit/ward during the time of acquisition. Thus, it is just as likely that transmission occurred from a contemporaneously colonized patient via the hands of a clinician than a prior room occupant. This doesn't discount the need to clean rooms more effectively, but it does suggest we need to consider other factors in our causal models and not just analyze the "exposure of the moment," which in this case is the prior room occupant.

  2. Excellent point--the only study I read recently is the Nseir study, since it is MDR-GNRs I'm reviewing. That group did control for colonization pressure. Indeed, for two of the three MDR-GNRs they looked at, the colonization pressure was statistically significantly lower among the non-acquirers, though that variable was not significant in the final models.

    Of course, even if an organism is awaiting the newly arriving patient on an inadequately disinfected surface, a HCW's hands may still be the final transmission vector!

  3. Thanks Dan. The Nseir paper is a very nice study. I just reviewed the analysis and realized there are several issues with the study that are worth some mention.

    The first is that it appears that higher colonization pressure is significantly associated with ESBL or Acinetobacter acquisition, but not MDR-Pseudomonas. Second, prior room occupant is a risk factor for MDR-Pseudomonas and Acibetobacter, but not ESBL. Finally, I suspect the colonization pressure and prior-room occupant would be colinear, meaning that times with higher colonization pressure would be associated with higher unit-level transmission and thus associated with higher levels of prior room occupancy positivity. Thus, they probably should not be placed in the same regression model. It might have been best if they had published two models for each organism: one with only prior-room occupant in the model and another one with only colonization pressure in the model.

    This is an example of why people should draw causal diagrams before doing multivariable regression. Either way, this suggests that the evidence of prior room occupancy as a risk-factor for acquisition of MDR-bacteria is limited at this point.

  4. Further clarification:

    Prior-room-occupant = one patient colonized with the MDRO
    Colonization pressure = all other patients colonized with the MDRO