Test products
In the positive list of the SFHH 51 products are listed as effective for hygienic hand disinfection, most of them with 3 ml for 30 s (48%), followed by 6 ml for 60 s (17%), 6 ml for 30 s (10%), 3 ml for 15 s (10%) and other applications (15%) [4]. We therefore selected from products with the most common type of application (3 ml for 30 s). The following products with a rather low concentration of alcohol were used in the study be because they are frequently used in French hospitals: Aniosgel 85 NPC, manufactured by Laboratoires Anios, Lille, France (coded as product 1), Aniosrub 85 NPC, manufactured by Laboratoires Anios, Lille, France (coded as product 2), and Clinogel derma+, manufactured by MEDA pharma, Paris, France (coded as product 3). Products 1 and 2 contain ethanol (70%, w/w), product 3 contains ethanol (60%, w/w) in combination with isopropanol (15%, w/w). All three products are listed as effective by the SFHH for hygienic hand disinfection with 3 mL in 30 s [4]. They are also described as virucidal in 30 s (products 1 and 2) or 1 min (product 3) [4].
Bactericidal efficacy according to EN 1500
One set of experiments was performed with blinded formulations at HygCen International GmbH (Bischofshofen, Austria), one set with blinded formulations at the Institute of Hygiene and Applied Immunology of the Medical University (Vienna, Austria) and one set at Bode Chemie GmbH (Hamburg, Germany). All participants gave informed written consent. The bactericidal efficacy of each hand disinfectant was compared to the reference isopropanol 60% (v/v) in three separate cross-over experiments on artificially contaminated hands, two of them with 15 volunteers in two different laboratories (EN 1500 version 1997) [9] and one with 20 volunteers in a third laboratory (prEN 1500 version 2009) [10]. In each experiment subjects were randomly assigned to receive either test product or reference as the first application, with half of the volunteers receiving test product first, and the other half receiving the reference alcohol first. As per cross-over design, in the second application the subjects received the other product within 3 hours.
For artificial contamination, hands were washed for one min with soft soap, dried with paper towels, immersed in the Escherichia coli contamination fluid up to the mid-metacarpals for 5 s with fingers spread, and allowed to dry for 3 min [11]. To determine pre-decontamination values, fingertips from both hands were rubbed for one min in a separate petri dish containing liquid broth. Either 1 × 3 mL of test product or 2 × 3 mL of reference alcohol was applied to the hands. Test products were rubbed into the hands for 30 s, and reference alcohol for 2 × 30 s. The EN 1500 hand rubbing technique was used [9]. Post-decontamination values were determined immediately after the rub-in period using petri dishes containing liquid broth with neutralisers (3% Tween 80, 3% saponin, 0.1% histidine, 0.1% cysteine). For both reference and test products, log10 counts from the left and right hands of each subject were averaged separately, for both pre-values and post-values. The arithmetic means of all individual log10 reduction values were calculated. For the experiments according to EN 1500 from 1997, the Wilcoxon matched-pairs signed rank test (one-sided) was used for pair-wise comparison between mean log10 values obtained with test product and the reference alcohol (significance level as described in the norm, p = 0.1) [9]. For the experiments according to prEN 1500 from 2009, the Hodges & Lehmann statistics was used to evaluate for non-inferiority of the test product compared to the reference procedure. A value > 0.75 log10 indicates inferiority of the product to the reference procedure [10].
Virucidal activity according to EN 14476
All experiments were performed at MikroLab GmbH, Bremen, Germany also without knowledge of the products examined. Product 1 was tested based on two blinded samples in a total of three independent test runs. Infectivity assays were done according to EN 14476 [12] with the following test viruses: poliovirus type 1 strain LSc-2ab, passaged and cultured in BGM cells (buffalo green monkey cells); adenovirus type 5 strain Adenoid 75, passaged and cultured in A549 cells (human lung epithelial carcinoma cells).
Tests were carried out in a water bath at 20°C. Three different compositions of test product, organic load and inoculum were evaluated based on the EN 14476 from 2005 [12] and the revised prEN 14476 from 2011 [13] (80 + 10 + 10; 90 + 9 + 1; 97 + 2 + 1, parts per volume). The appropriate volume of the test virus suspension and the appropriate volume of organic load (phosphate-buffered saline [PBS], Aqua bidest. for no organic load, or clean conditions [0.03% bovine serum albumin]) were mixed with the disinfectants. Clean conditions were incorporated because it was now introduced in the prEN 14476:2011 for hand rubs [13]. Immediately at the end of the chosen exposure time, activity of the disinfectant was stopped by serial dilutions with ice-cold cell culture medium. All controls required in the EN 14476 were incorporated.
Performing some determinations ready to use MicroSpin™ S-400 HR columns (GE Healthcare, Freiburg, Germany) were used in order to remove the cytotoxic agents according to instructions of the manufacturer. Examinations of the products and virus controls without columns were run in parallel.
Virus controls were incorporated after the longest exposure time. Here, the disinfectant was substituted by water of standardized hardness.
For determination of cytotoxicity of the disinfectants, the appropriate volume of Aqua bidest. was mixed with the corresponding volume of the disinfectant depending on the selected composition (final product concentration of 80%, 90%, or 97%), diluted with ice-cold cell culture medium and inoculated onto permissive cells. These controls were also performed with the different organic loads.
Infectivity was determined by means of end point dilution titration in a micro-procedure. For this, samples were diluted with ice-cold cell culture medium and 100 μL of each dilution were placed in 8 wells of a sterile polystyrene flat bottomed 96-well microtitre plate (Nunc A/S, 4000 Roskilde, Denmark) with a preformed monolayer. Cultures were observed for cytopathic effects after different days of inoculation. The infective dose (TCID50) was calculated according to the method of Spearman (2) and Kärber (3). Titre reduction is presented as the difference between the virus titre after defined contact time with the product and the virus titre of the control. This difference is given as log10 reduction. A reduction of infectivity of ≥ 4 log10 steps (inactivation 99.99%) was regarded as evidence for sufficient virucidal activity against the tested virus [12].