To the Editor—We very much appreciate Dr. Stephanie Dancer’s comments related to our recent report, “Evaluating a New Paradigm for Comparing Surface Disinfection in Clinical Practice.”Reference Carling, Perkins, Ferguson and Thomasser ¹ Dr. Dancer is regarded the world over for her expertise, research, and advocacy related to improving patient safety through mitigating transmission of healthcare-associated pathogens from near-patient surfaces to susceptible hosts. We welcome the opportunity to respond to several points she raised in her letter.Reference Dancer ²

The methodological considerations she posed included the potential that the low heterotrophic bioburden (HBB) we found could have been a reflection of habitual exposure of environmental surfaces to disinfectants; differences in sensitivity between dip slides and swab cultures; potential shortcomings in the manner in which dip slides were used; and possible improved sensitivity of the dip slide system with 48 hours incubation vs 24 hours. All have validity and are worth considering in future studies. Given the essential identical thoroughness of cleaning and large number of data points in both arms of our study, we believe that the magnitude of the analysis and the manner in which the dip slide system was used led to a symmetrical distribution of any confounding variables that might have adversely affected the sensitivity of our quantitative findings. Indeed, the magnitude of the difference in potency between the 2 disinfectants (ie, the novel disinfectant was 1.93 times more potent than the quaternary ammonium disinfectant) and the high level of the relative difference (P<.0001) between the disinfectants clearly support the sensitivity of the dip slide system as it was used. Because the kinds of comparative studies for which this new paradigm may be used to compare the effectiveness of interventions may have substantially less differences between the 2 interventions, maximizing the sensitivity of the sampling system employed will be an important consideration in future studies.

While limitations in the length of our report precluded a more in-depth discussion related to hygienic standards, it is important to note that the study was not designed to directly analyze this issue. Our findings, by chance, provided further observations regarding the challenges of using HBB independently as a cleanliness standard, and we addressed the issue in the discussion section of our report.

As has been noted in the pastReference Carling ³ and as recently as this year,Reference Nerandzic, Thota and Sankar ⁴ many published reports have observed, as we did, that the generally low HBB on healthcare surfaces appears to limit the potential for assessing the effectiveness of surface cleaning practice unless it is performed on a comparative basis, as we did. We support Dr. Dancer’s hope that “future work will demonstrate which density adequately reflects risk in a range of healthcare environments.”Reference Dancer ^{2 ,} Reference Carling and Huang ⁵ In addition, the concern that ongoing use of disinfectants over time can decrease residual HBB has recently been raised.Reference Dancer ⁶ Further work in this area, particularly with the new disinfectants that do not damage patient area surfaces,Reference Deshpande, Mana and Cadnum ⁷ needs to be conducted.