How Clean Is Clean Enough -- And How Do We Get There?

Allison H. Bartlett, MD


December 29, 2014

Editorial Collaboration

Medscape &

Evaluation of a Sporicidal Peracetic Acid/Hydrogen Peroxide-Based Daily Disinfectant Cleaner

Deshpande A, Mana TS, Cadnum JL, et al
Infect Control Hosp Epidemiol. 2014;35:1414-1416


Evaluating a New Paradigm for Comparing Surface Disinfection in Clinical Practice

Carling PC, Perkins J, Ferguson J, Thomasser A
Infect Control Hosp Epidemiol. 2014;35:1349-1355


Evaluating Cleaning Products and Processes

Surfaces near patients are increasingly being recognized as important links in transmission of healthcare-associated infections (HAIs). It seems obvious that clean surfaces pose a lower risk for transmission than contaminated surfaces, but the relative contributions of different cleaning products, application devices, and new technologies are not clear.US Environmental Protection Agency-approved disinfectants must demonstrate efficacy against viruses, bacteria, and spores, but there is no requirement to assess the clinical effectiveness of a product.

These two recent studies discuss the efficacy of a peracetic acid/hydrogen peroxide (PA/H2O2) disinfectant in a clinical setting and describe a method for head-to-head comparison of the clinical effectiveness of cleaning products.

Deshpande and colleagues compared the efficacy of a PA/H2O2 sporicidal disinfectant (OxyCide™; Ecolab; Martinsburg, West Virginia) with a 1:10 dilution of bleach against vancomycin-resistant enterococcus (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and Clostridium difficile spores in a laboratory setting. PA/H2O2 effectiveness was not affected by the presence of organic material (fetal calf serum), whereas bleach was significantly impaired by the presence of organic material. When used in a clinical setting, both bleach and PA/H2O2 eliminated C difficile, MRSA, and/or VRE contamination on bed rails and bedside tables. On floors where it was compared with a quaternary ammonium disinfectant , only PA/H2O2 significantly reduced C difficile, MRSA, and/or VRE contamination.

Carling and colleagues developed a method for simultaneous assessment of both cleaning process and cleaning products. A fluorescent marker (DAZO®; Ecolab) was placed on 12 high-touch surfaces before routine discharge cleaning with PA/H2O2 (OxyCide or a quaternary ammonium disinfectant. A black light was used to determine whether the fluorescent marker had been completely removed after cleaning ("process"). Furthermore, agar dip slides were used to compare the aerobic bacterial colony counts on surfaces adjacent to the fluorescent marker before and after cleaning. This allowed the investigators to look at the ability of the two different disinfectants to reduce bacterial burden ("product")—while controlling for whether the room surfaces were wiped sufficiently ("process").

The percentage of surfaces cleaned during the study (fluorescent marker removal) was the same in rooms cleaned with a quaternary ammonium disinfectant (66.4%) and PA/H2O2 (65.3%). More surfaces cleaned with PA/H2O2 than the quaternary ammonium disinfectant had complete removal of bacterial burden (77% vs 40%). Because the thoroughness ("process") of cleaning was equal in the two groups, the increased effectiveness (1.93 times) is likely due to the increased efficacy of PA/H2O2.


A significant limitation of these studies is the universal lack of data defining the relative risk for transmission of healthcare-associated pathogens based on specific levels of microbial contamination of surfaces (bio-burden).

Given that there is no evidence-based standard of "how clean is clean," interpretation of the reduction in bacterial burden is unclear. Some have suggested using the same threshold as in food preparation surfaces (<2.5 colony-forming units [CFU]/cm2), but whether this level of contamination is associated with a lower risk for transmission of healthcare-associated pathogens is unknown. In this study, only 1.7% of cleaned surfaces would have been defined as a failure (>2.5 CFU/cm2), and 85% of surfaces would have been counted as "clean" prior to actual cleaning. Stated another way, using only post-cleaning colony counts, 98% of surfaces would be declared "clean," whereas using the fluorescent marker showed that only 66% of surfaces were "cleaned."

Whether the increased effectiveness of PA/H2O2 compared with the quaternary ammonium disinfectant or 1:10 dilution of bleach will result in clinical reductions in transmission of environmental pathogens and improved patient outcomes requires further evaluation. However, the technique described by Carling and colleagues, which pairs evaluation of thoroughness of cleaning (using fluorescent marking) with effectiveness of the cleaning product itself (using colony counts from dip slides), is novel. The study authors commented on the potential for using this paradigm to study the relative clinical efficacy of other cleaning and disinfection products, materials, and technologies. Are microfiber cloths better than paper towels? Are disposable disinfectant wipes better than towels soaked in disinfectant?

This brings us back to the important question: Does it matter for patients? We don't have the answers yet, but the techniques described in these articles, combined with studies evaluating the impact of "better cleaning" on patient outcomes, will be instrumental to advancing the science of preventing HAIs.


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