Because cross-transmission by healthcare worker (HCW) hands is involved in a large proportion of healthcare-associated infections, hand hygiene is considered critical by both the Centers for Disease Control and Prevention and the World Health Organization.Reference Pittet, Allegranzi and Sax 1 – Reference Boyce and Pittet 3 Over the past 20 years, alcohol-based handrubs (ABHR) have become the preferential tool for hand hygiene in healthcare settings because of their high antimicrobial efficacy, tolerability, and accessibility.Reference Pittet, Allegranzi and Sax 1 – Reference Boyce and Pittet 3 There is common sense and microbiologic evidence that the volume of ABHR used should be large enough to cover the whole surface area of both hands, but there is no consensus on how much is the minimum necessary, and whether HCW hand size influences it.Reference Laustsen, Lund, Bibby, Kristensen, Thulstrup and Møller 4 – Reference Hautemaniere, Cunat and Diguio 7 The objective of this study was to evaluate whether the amount of ABHR used by HCWs for handrubbing impacts the residual concentration of bacteria on their hands according to their hand size.
METHODS
We conducted a laboratory-based experimental study at the University of Geneva Hospitals, using 15 healthy HCWs from the infection control program with extensive training and expertise in hand hygiene. In the experiment, hand hygiene action was completed under the close supervision of 2 senior infection control experts. HCWs had their hand surface area calculated by standard methods and classified as small (≤375 cm2), medium (376–424 cm2), or large (≥425 cm2).Reference Yao-Wen and Chi-Yuang 8
We used the reference strain Escherichia coli ATCC 10536 grown according to the European Norm 1500 standard (EN 1500) 9 to obtain a homogeneous bacterial suspension containing from 2.0×108 to 2.0×109 colony-forming units/mL. Prior to each contamination procedure, participants were asked to wash their hands with 5 mL of plain soap for 1 minute. Hands were contaminated artificially by inserting them into the bacterial suspension up to the mid-carpals for 5 seconds, and then, held up to dry for 3 minutes. After the first contamination procedure, baseline bacterial recovery was obtained using the fingertip method. As a next step, participants washed their hands, recontaminated them in the same way as before, and undertook a hand friction action with no ABHR using the World Health Organization recommended sequence for hand hygiene. 2 Following the process above, a second baseline recovery of bacteria was performed.
After these 2 measurements were taken, participants applied the reference EN 1500 ABHR (2-propanol 60%) varying every 0.5 mL from 0.5 to 3 mL. HCWs with large hands were investigated further with the application of 4, 5, and 6 mL of ABHR. At each application stage, the ABHR test volume was dispensed into the dominant hand of the HCW, and then the recommended World Health Organization sequence was followed for 30 seconds. After each action, the surviving bacteria were recovered from the participant’s dominant hand. At the end of the experiment, HCWs were asked to wash their hands with a 2% chlorhexidine handwash for 2 minutes.
Each sample was studied in a minimum of 4 different dilutions to accurately estimate bacterial counts. After dilution, 1-mL samples were distributed in tryptic soy agar plates within 30 minutes of recovery and incubated for 24 to 48 h at 36°C ±1°C. Bacterial colony-forming units were counted by visual inspection of each plate, adjusted for the corresponding dilution factor, and converted to log10. For each HCW and volume of ABHR applied, a log10 reduction was calculated.
We used a generalized linear mixed model with a random effect on the intercept and on the slope for the volume, to assess the log10 reduction depending on hand size (continuous and categorical formats) and volume of ABHR. Statistical analyses were performed using Stata/IC, version 13 (StataCorp). Statistical significance was defined as P<.05 (2-sided).
RESULTS
Four participants had small hands (mean [SD] hand surface area, 332.9 [22.2] cm2), 6 had medium hands (404.2 [9.7] cm2), and 5 had large hands (473.2 [40.4] cm2). Overall, the mean (SD) level of contamination of hands at baseline was 6.2 (0.58) log10 and there was no difference between the hand size categories (P=.372).
Figure 1A shows the interquartile E. coli log10 reduction observed according to the volume of ABHR applied. The mean reduction of bacterial count was 0.28 log10 for each additional increase of 0.5 mL of ABHR (95% CI, 0.20–0.36, P<.001). Bacterial reduction was inversely and significantly associated with hand surface area (−0.003 [95% CI, −0.006 to −0.0005], P=.019).
FIGURE 1 A, Median bacterial reduction (interquartile log10) on healthcare worker hands according to the volume of alcohol-based handrub applied for 30 seconds using the World Health Organization technique (n=15). B, Mean bacterial reduction on healthcare worker hands according to hand size categories and the volume of alcohol-based handrub applied for 30 seconds using the World Health Organization technique (n=15). E. coli, Escherichia coli.
Figure 1B shows the mean log10 reduction of E. coli per hand size group according to the volume of ABHR applied. The log10 reduction was significantly different by hand size category (interaction term P=.01): the mean log10 reduction per each additional 0.5 mL of ABHR was 0.40 (95% CI, 0.27–0.52, P<.001) in the small hand size category, 0.32 (0.21–0.42, P<.001) in the medium hand size category, and 0.15 (0.03–0.26, P=.011) in the large hand size category. Figure 2 shows E. coli log10 reduction per participant with large hands according to the volume of ABHR applied, including larger volumes—that is, 4, 5, and 6 mL.
FIGURE 2 Bacterial reduction on hands among healthcare workers with large hands according to the volume of alcohol-based handrub applied for 30 seconds using the World Health Organization technique (n=4). E. coli, Escherichia coli.
DISCUSSION
Significant efforts have been made globally to improve hand hygiene compliance in healthcare. 2 , Reference Pittet 5 At this time, however, there is a need to move the issue further forward by improving the quality of hand hygiene technique and antimicrobial efficacy, considering the evidence that a poorly performed hand hygiene action is less effective and may compromise patient safety.Reference Laustsen, Lund, Bibby, Kristensen, Thulstrup and Møller 4 , Reference Pittet 5
This experimental study demonstrates a strong relationship between the reduction of bacterial count on hands and the amount of ABHR used for hand hygiene, taking into account the hand surface area. It is a matter of concern that HCWs with large hands could not achieve a minimum of 2 log10 reduction of bacteria on their hands by the application of 3 mL of ABHR, the volume recommended by most manufacturers. That concern gets greater when we realize that the mean application volume of ABHR in clinical practice may be lower than 1 mL.Reference Leslie, Donskey, Zabarsky, Parker, Macinga and Assadian 10
Our results are significant: under the strict experimental conditions of our study design, even one of the most powerful ABHR available, applied under controlled conditions by trained, supervised experts, did not reach the expected bacterial reduction when the volume applied was not adapted to the hand size, a parameter yet unrecognized in daily clinical practice.
Our study has some limitations. First, we tested only one strain and one ABHR; further testing is necessary to verify whether these findings could be generalized to other pathogens and other ABHR formulations. Second, we did not test the effect of poor or suboptimal hand hygiene technique. This could be assessed in the future. Finally, the minimum reduction of bacteria necessary to avoid transmission between patients through HCW hands, or from a dirty to clean body site within the same patient, remains a matter of debate.Reference Pittet, Allegranzi and Sax 1 Future studies should address this question and ultimately clarify the clinical relevance of our study findings; further evidence between microbiologic efficacy and clinical effectiveness should be provided.
In conclusion, this study demonstrates that the volume of ABHR applied on the hands of HCWs was associated with the microbiologic efficacy of the hand hygiene procedure, and that the HCW hand size significantly affects that association. These results suggest the need for customizing the volume of ABHR used for hand hygiene actions according to the size of HCW hands to ensure appropriate hand antisepsis and, possibly, patient safety.
ACKNOWLEDGMENTS
We acknowledge all the HCWs who participated as volunteers in the present study, and Ross Leach for his substantial editing contribution to the manuscript.
Financial support. Infection Control Programme, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
Potential conflicts of interest. All authors report no conflicts of interest relevant to this article.
