Attacking the fecal veneer (part 2)

Last year (Jan 17, 2017) I blogged on an excellent pragmatic cluster-randomized crossover study in which 4 patient room cleaning strategies were tested for their effectiveness to reduce acquisition of bacterial carriage for the incoming patients. The authors’ conclusion was that “enhanced terminal room disinfection decreases the risk of pathogen acquisition”, which I interpreted as “Not for C. diff, may be for MRSA and yes for VRE.” Now the same group published the effects of these interventions on infection/colonization with these pathogens in ALL patients admitted to the hospital during the study period, see. Authors’ conclusion this time: “Enhanced terminal room disinfection with UV in a targeted subset of high-risk rooms led to a decrease in hospital-wide incidence of C difficile and VRE.” Really?

In this study they tested 4 strategies, each during 7 months, in random order in 9 hospitals in single-patient rooms from which a patient on contact precautions had been discharged or transferred. The outcome was acquisition of C. diff, MRSA, VRE or multiresistant Acinetobacter for the incoming patient.

The 4 strategies:

Disinfection with quaternary ammonium-containing disinfectant (reference);

Reference + a UV-C device (UV-group);

Disinfection with a hypochlorite-containing disinfectant (bleach group);

UV+bleach

In their first paper they had – in just over 2 years – 31,226 (!!!!!) rooms that met the inclusion criteria, yielding 21,395 patients with 97,833 exposure days. Impressive? In the same period they also had 271,740 unique patients with 314,610 admissions meeting all inclusion criteria. With this population they performed a prespecified analysis for the secondary outcomes hospital-wide, hospital-acquired incidence of all target organisms (no. of patients with/10,000 patientdays), and hospital-wide, hospital-acquired incidence of each target organism separately. Initially I thought that the word “infection” had been erroneously deleted at some places. Yet, an incident case was defined upon a positive clinical culture or test with one of the target organisms, considering all microbiological cultures (screening was not performed during the study). So, it is suggested that we look at infections, where it most probably reflects colonization for most cases.

The prespecified analysis revealed that: “Overall, there was no significant difference between standard disinfection and the three enhanced terminal disinfection strategies in the hospital-wide risk of target organism acquisition for all multidrug resistant organisms.” Relative risks, compared to the reference period: 0∙89 (0∙79 to 1∙00) p=0∙052 for UV-period; 0∙92 (0∙79 to 1∙08) p=0∙32 for the bleach period; 0∙99 (0∙89 to 1∙11) p=0∙89 for bleach+UV period. So, that’s a result that can easily be conveyed, I thought.

But then they went deeper into the specific pathogens, and it all starts to get cloudy: For C diff there was reduction in the UV period (RR 0∙89, 95% CI 0∙80–0∙99; p=0∙031, compared to reference), but not in the bleach period (RR 0∙91, 0∙75–1∙10; p=0∙32) or in bleach and UV period (0∙97, 0∙84–1∙12; p=0∙68). Bleach blocks UV?

For VRE incidence was significantly lower in the UV  period (than in reference) study period. But wait a minute, the incidence was 3∙23/10,000 patient days vs 3∙24/10,000 patient days; yielding a RR of 0∙56, 0∙31–0∙99; p=0∙048? Read again! These are the numbers from Table 2 and the text, without further clarification.

And then I got really lost as they presented a post-hoc analysis in which admitted patients were stratified upon the cleaning procedure of their room (UV or not) after the previous patient left and the carriage status of that prior patient (seeding or not). Most got into a room not cleaned with UV light and most rooms had not contained a seeder. In this analysis UV-light cleaning was with lower risks for C. diff and VRE. And that finding ended up prominently in the conclusion.

So, what to do now…….? This great study – for the first time – still provides measures of relative effectiveness of disinfection procedures. A strong signal came from the initial study for preventing acquisition with VRE in rooms that had been occupied by VRE carriers. This second analyses looking at the – so important – overall effect in the hospital is actually straight negative for the predefined primary endpoint, inconsistent for the predefined secondary endpoints and – to me – non-interpretable for the post hoc analysis. Taking that as evidence for UV-light strategies to reduce hospital-wide evidence of C. diff and VRE infections, as the authors do, looks like a clear case of “blinded by the light”.

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