Our results show that an alcohol-only handrub that contains an optimized composition of two alcohol species, ethanol and n-propanol, achieved a significantly greater initial microbial reduction after surgical hand preparation than a CHG-alcohol combination handrub when tested according to a modified EN 12791 protocol, and that a significant difference in reduction factors in favor of the alcohol-only rub was maintained for 6 h under surgical gloves. These results are consistent with findings from a previous comparative study , in which an 80% (w/w) ethanol-only rub passed EN 12791 requirements both immediately and at 3 h after application, while the same 1% (w/w) CHG and 61% (w/w) ethanol combination rub as was used in the present study failed at both time points. Among the three common alcohol species (ethanol, isopropanol and n-propanol) that are used for hand and skin antisepsis, n-propanol has the most potent general microbicidal activity and exerts this at relatively lower concentrations . This supports its inclusion into alcohol-based handrubs and explains the potent activity exhibited by a combination of n-propanol and ethanol at an overall concentration of 63% (w/v) in product A as observed in the present study.
The results in this study were obtained despite the absence of CHG in handrub A, despite the extended test interval of 6 h under surgical gloves and despite the fact that handrub B was given a very substantial a priori advantage by having had twice the initial application time (180 s) of handrub A (90 s), with the application volume (3 × 3 ml) and other conditions being equal. These findings are consistent with earlier findings indicating that the application of alcohols, despite the absence of residual activity per se, is followed by substantially delayed regrowth of skin flora or even continued microbial killing [23, 24] and that the contribution of dedicated supplements for persistency is relatively modest or even absent when tested for durations of up to 6 h [25, 26]. This is further consistent with the concept that an initially strong and immediate microbial killing capacity continues to translate into low viable microorganism numbers for several hours under surgical gloves. The extended duration of 6 h under surgical gloves was chosen for the present experiments, instead of the usual 3 h for EN 12791, in order to simulate tougher test conditions that resemble those of the US ASTM E1115 standard in this aspect. Furthermore, our results as well as those of others [11, 27] support shorter application times, as short as 1.5–2 min, when highly potent alcohol-based handrubs are used.
In addition to using an effective alcohol-based handrub, the technique of application is also considered important . While EN 12791 requires coverage of only the hand surfaces for the purpose of efficacy testing, the World Health Organization hand hygiene guidelines  state that complete coverage of hands and forearms requires about 15 ml (about 3 × 5 ml) and emphasize that it is important to keep hands and forearms wet with alcohol for the entire duration of application. Some protocols that include very small applied volumes  are therefore a cause for concern, as they are likely to lead to incomplete skin surface coverage and interrupted action of the antiseptic.
In the area of skin antisepsis, CHG has been the subject of a considerable amount of incorrect assessment. What had happened was that a substantial proportion of the clinical trial-based literature on skin antisepsis had attributed favorable clinical outcomes achieved with CHG-alcohol combinations (two effective antiseptics) to CHG alone and concluded that CHG alone (instead of the combination) was the agent supported by evidence [30, 31]. This had happened despite a strong microbiological literature base that showed alcohols to be potent antiseptics. The misinterpretation of trial outcomes was carried over into prominent guidelines, led to a number of prominent recommendations for CHG alone, and created widespread but in parts unsubstantiated views of CHG as an “in” antiseptic.
Microbiological assessment of antiseptics may similarly be subject to errors. Both European and US standards stipulate that adequately validated neutralizer substances must be used at the point of sampling after antiseptic exposure ; this is in order to prevent continued killing due to residual bacteriostatic or bactericidal action after the end of the dedicated exposure. While this applies to the testing of all antiseptics, CHG in particular is prone to false-positive efficacy assessment in the absence of adequate neutralization, due to strong bacteriostatic activity that it exerts at concentrations far below bactericidal levels [32,33,34]. It has been suggested that this is a factor that likely led to a systematic skewing of the antiseptic literature . Previous reports of superior performance of CHG-alcohol combination rubs for surgical hand antisepsis [16, 17] indeed attracted letters to the editor that expressed concern about adequate neutralization [18, 19]. In the present study, adequate neutralizers were used during the entire testing process, thus creating equal sampling conditions for both comparator rubs.
Among the different hand hygiene agents, alcohol-based handrubs are generally most well tolerated on skin; true alcohol allergies have not been documented beyond reasonable doubt, and irritant contact dermatitis from alcohols is rare when handrubs are well formulated with emollients . On the other hand, CHG is a known allergen and a frequent cause of irritant contact dermatitis among healthcare personnel [2, 36, 37]. It has also been the subject of a recent US FDA warning about rare but serious anaphylactic reactions . Thus, there is a clear potential for a tolerability advantage from alcohol-only handrubs for surgical hand preparation, especially if their antimicrobial performance characteristics are equal to or even better than those of CHG-containing ones.
It is a limitation of our study that it was performed according to a modified EN 12791 protocol, and results from EN 12791 testing do not necessarily translate into congruent results according to the US standard ASTM E1115 , mainly due to the US standard’s requirement for incremental increases (cumulative effects) in log reduction factors on subsequent days of testing [15, 39]. However, the clinical relevance of this requirement has been questioned, because it is not intuitive why a surgeon’s hands after antisepsis should be permitted to have different microbial counts on different working days of the week . In any case, EN 12791 is a very stringent standard in which only very potent handrubs tend to pass, and it has high inter-laboratory reproducibility .