Evidence-based hand hygiene: Liquid or gel handrub, does it matter?

Participants

All participants in this study were medical students (N = 340) of the Semmelweis University (Budapest, Hungary). All students who attend class at our clinic were invited to participate in the study, voluntarily. Students undertook a short course on hand hygiene, after which they received individual RFID cards to record their individual data (Table 1).

Table 1 ABHR included in the evaporation rate measurementExperimental settings

Measurements involved giving participants pre-determined, randomly assigned, exact volumes (1.5 or 3 ml) of either liquid or gel disinfectant (Table 2). A Dispensette S Analog-adjustable bottle-top dispenser (Brand GmbH, Germany) was used to apply the liquid, while a calibrated Purell ADX-7 (GOJO Industries Inc., Akron, OH) dispenser was used for the gel. Disinfectants were placed on the centre of the dominant hand’s palm. All measurements were performed under the direct supervision of a qualified investigator. Participants did not get any instruction on how they should rub their hands, they were only asked to reach complete coverage. Students were previously trained to follow the WHO 6-step protocol [1].

Table 2 Gel versus Liquid Investigation ArrangementsIn vitro evaporation rate investigation

During the study, we compared two commercially available ABHR products. In order to exclude any possible bias, and to prove the findings can be generalized, regardless of ABHR brand, an in vitro evaporation rate investigation of commercially available products was conducted.Evaporation rates were examined on two typically applied volumes (1.5 and 3 ml) on three different sized Petri dishes (surface areas: 7.07, 19.63 and 38.48 cm2). To assess the evaporation rates, disinfectants were first taken to Petri dishes. Then, to replicate the hand temperature, the covered Petri dishes were placed on a heater, adjusted to 34 °C [27, 28]. The mass of the disinfectant was measured when the cover was removed, and every 30 s after, for up to 3 min. Evaporation was calculated by subtracting the mass registered every 30 s from the initial mass at t = 0. Measurements occurred under standard ambient laboratory conditions (25 ± 3 °C, 30 ± 5% humidity) and were repeated 5 times with each handrub (Fig. 1). The list of the investigated commercial handrubs can be found in Table 1.

Fig. 1figure 1

Evaporation rate measurement setup

Hand coverage measurements

Distribution, and consequently hand coverage differences between liquid and gel formulated ABHRs were measured employing an innovative electronic and completely automated digital health technology system (Semmelweis Hand Hygiene System, HandInScan Zrt., Debrecen, Hungary), which has been shown to be superior to any human expert-based evaluation method [29]. Furthermore, application times, volume awareness and disinfectant spillage were also assessed for every single hand hygiene event.

The Semmelweis Hand Hygiene System (Fig. 2) can evaluate the disinfectant’s coverage on the hand. By adding a fluorescent dye to the handrub, whether it is a liquid or gel based one, the device can detect the covered (and validly disinfected) areas with a pixel sized resolution. The system presents an immediate and quantitative feedback for health care workers to examine their hand rubbings’ efficiency.

Fig. 2figure 2

Measurements using the Semmelweis System, where green indicates handrub-covered areas, red indicates non-covered areas determined by an AI algorithm, based on image analysis performed on recorded hands, treated with an UV-dyed alcohol-based solution. (Image credit: HandInScan Zrt)

Both the gel and the liquid (Semmelweis Training Rub, Semmelweis Training Gel, Molar Chemicals Kft.) had a similar alcohol concentration (70% ethanol), and contained a small amount of fluorescent dye (< 0.02%). After the hand rubbing, participants' hands were assessed employing the Semmelweis System.

Hand size determination

Hand size for every participant was calculated by counting the pixels of the systems’ scanned images. Poor quality images were excluded from the evaluation. Hand surface (cm2) assessment was performed according to an already established Automated Area Assessment method [17], which estimates hand size by using a calibration to convert pixel counts to centimetres, and thus considers that the 3D surface of the hands is 1.36× bigger as their two dimensional projections.

Application time measurements

Application time was measured by a digital stopwatch. Participants were given a clear signal when to start the hand rubbing. As soon as participants felt that their hands were dry, they signalled to the investigator, who recorded and documented the exact time.

Volume awareness

Adjacent to the physical experiments, participants were surveyed on how the given disinfectant volume felt (Subjective Volume Awareness Assessment, presented in Table 3), before the hand rubbing’s evaluation with the Semmelweis System. The participants were not informed about the exact volume they were given during the experiments.

Table 3 Subjective volume awareness assessmentDisinfectant spillage

To assess the disinfectant spillage, a custom experiment design including an A3-size paper was used. Participants were required to perform hand rubbing directly above the sheet of paper (66,329,742 celeste chiaro coloured paper, A3-size, 80 g/m2 grammage, Fabriano, Italy) at approximately 20 cm height. After an extensive drying period, papers were photographed using a camera equipped with a UV flashlight. The disinfectant droplets that stained the paper were fluorescent, therefore could be assessed using suitable software evaluation (segmentation with custom written segmentation algorithm in Python). Utilizing control measurements as a reference, the spillage was evaluated according to the fluorescence patches’ overall intensity and area. Additionally, students were asked whether they felt the disinfectant dripping from their hands during the hand rubbing process (Table 4). The setup was built so that participants could not directly verify the spillage with their own eyes.

Table 4 Disinfectant spill testStatistical analysis

For the statistical analysis, R Core Team: R: A Language and Environment for Statistical Computing (R Foundation for Statistical Computing, Vienna, Austria R Version: 4 Released: 2020.04.24) was used. According to the predictor and outcome variables, different statistical tests were chosen. To investigate hand coverage, two models were investigated, one where the missed surface area that larger 0% was handled as continuous variable and the other, where surface area was handled as binary variable (0% missed and not 0% missed). In the first case, a linear mixed effect model was utilised, in which predictor values were handrub volume, type and subjective volume awareness, while the outcome variable was the logarithm of the missed surface area (%). In the second case, we utilised a generalized mixed effect model with logit link. In this model, again, the predictor values were handrub volume, type and subjective volume awareness while the outcome variable was the binary value of the missed surface area. For both cases, we adjusted for hand size and for the type of the first used handrub.

Random intercept was assigned to the different participants. Compound symmetry correlation structure for handrub amount and different power variance structure for handrub at different participants were used to fit the final model.

When examining the correlation of handrub type and volume to drying time and disinfectant spillage, a linear mixed effect model was used, where the outcome variables were the logarithm of the drying time and the fluorescence coverage, respectively.

Results are presented as mean along with ± 1 standard deviation.

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