Sidney W. Bondurant MDa, Collette M. Duley BSb, John W. Harbell PhDc Demonstrating the persistent antibacterial efficacy of a hand sanitizer containing benzalkonium chloride on human skin at 1, 2, and 4 hours after application Sidney W. Bondurant MDa, Collette M. Duley BSb, John W. Harbell PhDc a University of Mississippi Medical Center, Jackson, MS b BioSciences Laboratories, Inc., Bozeman, MN c EAS Consulting Group, Dallas, TX American Journal of Infection Control 47 (2019) 928−932

Background/Overview What was the purpose of the research? Consider - Does the problem have significance your practice? Use of hand sanitizers has become a cornerstone in clinical practice for the prevention of disease transmission between practitioners and patients. Traditionally, these preparations have relied on ethanol (60%-70%) for bactericidal action. Applied to the skin, the ethanol-based sanitizers are effective in reducing the bioburden of many types of microbes. However, alcohols are volatile and can evaporate from the skin’s surface, so the residual antibacterial activity may be limited.

Study Objectives/purpose Ask yourself – how will this impact my practice if the study is valid? PURPOSE: The purpose of this study was to evaluate the residual antibacterial efficacy of one test product (DAB hand sanitizer, 0.12% benzalkonium chloride (BK)) verses a comparator ethanol-based product (63 % ethyl alcohol), as determined by the difference between the number of challenge bacteria species recovered following exposure to the test materials and the number recovered from the untreated (negative control) test sites. Often the last line of the abstract gives the authors answer to the research question.

Methods Population Study design: Experimental Each patient part of both test and control group Randomization occurring in selection of volar forearm spaces assigned to test/control/comparator products Population 24 volunteers with healthy skin Age 19-63 years old 16 men and 8 women Study design – is the design appropriate for the research questions? Is the study design descriptive or analytical? What measures of disease or risk you can deduce from different design types? Be familiar with the strengths and weaknesses of different study designs. Population – look at inclusion/exclusion criteria – are they clearly defined? Is the population appropriate for the research questions? Can the results of the study be translated to the general population? Bias – is the research method exposed to bias? Has randomization been used to reduce bias? Do the authors acknowledge any inherent bias? What is the intervention the authors are testing? What is the outcome they are measuring? Is it appropriate within the study design? How are the variables measured? Statistical analysis – did the authors choose an appropriate test for the variables they are testing? Is a rationale provided for the use of selected statistical tests? What significance levels are they using? Has the power of the study been stated and is the study appropriately powered, i.e. sample size, to eliminate errors? statistical power is the likelihood that a study will detect an effect when there is an effect there to be detected. If statistical power is high, the probability of making a Type II error, or concluding there is no effect when, in fact, there is one, goes down. Statistical power is affected chiefly by the size of the effect and the size of the sample used to detect it. Bigger effects are easier to detect than smaller effects, while large samples offer greater test sensitivity than small samples.

Methods (Continued) Intervention: S aureus was used as the test organism since it is a known skin pathogen. The test and comparator products were applied to defined areas of opposing forearms at 0.039 mL/cm2. Within those areas, 2-cm diameter circles were marked, to which the bacterial suspension would be applied at the specific times after application of the products. For the test product treatment, bacteria were applied at 1, 2, and 4 hours after product application and for the comparator product treatment, bacteria were applied at 1 and 4 hours after product application. Bacteria were applied to untreated skin at each time point to provide the baseline bacterial recovery.

Methods (Continued) Outcome measure: The number of colony forming units (CFU) from each site at each post-application time was converted to a log10 value. By definition, a CFU is one bacterium that is capable of continued replication to produce many bacteria to form a colony. Each inoculum to the skin contained approximately 106 CFU. Each sample from the skin was serially diluted and samples plated. Knowing the area of the skin sampled (3.46 cm2), the volume of SSF (5 mL), the dilution of the sample producing the counted plate, and volume of the sample added to the plate, the number of CFU per unit area on the skin could be calculated.

Methods (Continued) Statistical analysis The residual antibacterial activity was calculated by comparing the log10 value from the negative control site (time matched) to the log10 value from the test and comparator product-treated sites to determine the log10 difference (antibacterial effectiveness) for each treatment. The relative values were internally controlled for each subject. For the 1- and 4-hour postexposure times, the statistical significance between the log10 difference for the test and comparator values for the 24 subjects was evaluated using a paired Student t test (Excel).

Results

Results Are the results clearly stated? Is the result statistically significant (p value, CI)? The difference in the recovery between the test and comparator products was striking. Although the test product reduced bacterial viability by 3-4 log10 at each time point, the comparator product did not reduce bacterial viability by even 1 log10. The differences in efficacy were statistically significant at P < .001. These data suggest that the active ingredient BK (0.12%) can provide a marked improvement in persistent antibacterial activity over the 63% ethanol-based product.

Are the interpretations consistent with the results? Were the conclusions accurate and relevant to the problem the authors identified? Were the authors’ recommendations appropriate? Are study limitations addressed? Conclusion These results show a major improvement in persistent antibacterial activity for the BK formulation compared to the comparator ethanol-based formulation. Persistent antibacterial activity may be beneficial in the patient care setting to reduce the chances of incidental contamination of the hands and subsequent transfer to the patient.

Reviewer’s critique Study strengths Methods seem appropriate for objectives stated Weakness/limitations Small sample size Some of the references are relatively old Very narrow scope (also a strength?) Strengths – looking at sample size – study power, study design - Is the study design appropriate to answer the question? study population –generalizability, etc. Do the results support the conclusion? Consider statistical significance Weakness/limitations Also consider sample size, study designs, population - generalizability, statistical analysis, study bias What are the possible biases or flaws of the study? Do the authors acknowledge any limitations? End the JC presentation by assessing how the paper might impact the practice of infection prevention Ask the audience to discuss. Consider having discussion questions at the end of your presentation

Reviewer’s critique Does the study contribute to the body of knowledge? In healthcare: hand hygiene will take place at the same frequency independent of the residual effect of the antiseptic used. Would using this product make a difference in a patient care setting? Maybe in the setting of noncompliance… BK has been around for a long time. What is the reason it’s not already widely utilized as a hand sanitizer? Practice implications: Wait and see? Planned study: compare a 70% ethanol product and the test product from this study. Subjects will be medical clinic personnel, who will use both products in a cross-over study design. FDA final rule in 2020