Type of Alcohol
Isopropanol and ethanol both have in-vitro activity against bacteria, fungi and viruses. When tested at the same concentration, isopropanol is more efficacious than ethanol (1), however ethanol has greater activity against viruses than isopropanol (1, 47).
Alcohol-only ABHR versus alcohol-chlorhexidine ABHR
Although alcohols are rapidly germicidal when applied to the skin, they have no appreciable persistent or residual activity. The addition of a low concentration of chlorhexidine to an ABHR results in significantly greater residual activity than alcohol alone (1, 20) and therefore potentially improves efficacy. Notably, most published clinical studies that have demonstrated reductions in healthcare-associated infections (HCAIs) with the use of ABHR, have been associated with the use of ABHR that contains at least 70% v/v alcohol (isopropanol), 0.5% chlorhexidine and a skin emollient (10,11). To date there has been one published clinical study showing that alcohol-only ABHR is effective in reducing HCAIs (indeed, it is one of the formulations recommended by WHO), however this study was conducted in a developing healthcare setting using a product that has higher concentrations of alcohol than what is currently available on the Australian market (53). Further clinical studies in this area are encouraged.
There is a clear positive association between the extent of bacterial reduction and the concentration of alcohol contained in ABHR products. Furthermore the concentration for maximum efficacy is different for isopropanol than ethanol – e.g. ABHR containing 60% v/v isopropanol is associated with similar cutaneous bactericidal activity as ABHR that contains 77% v/v ethanol (20). Overall, however, the ideal ABHR is one that has an alcohol content of > 70% v/v (1).
When comparing alcohol concentrations it is important to look at the unit of measure, not just the numerical value of the concentration. Alcohol concentrations can be reported in a number of ways:
- Volume / Volume (V/V)
- Weight / Weight (w/w)
- Weight / Volume (w/V)
Conversion tables are available for comparison between V/V and w/w for ethanol only (49). A sample of ethanol labelled with a concentration of 70% V/V is equivalent to an ethanol sample labelled as 62.39% w/w (49).
Significant differences in the efficacy of ABHRs appear to be related primarily to a product’s overall concentration of alcohol (54) with higher concentrations being more efficacious.
The selection of an ABHR may be influenced by religious factors. According to some religions alcohol consumption is prohibited. ABHR with isopropanol appears more predictable in its lack of cutaneous alcohol absorption when compared with an ethanol-based AHBR, and may therefore be more acceptable to some religious groups (21).An awareness of commonly held religious and cultural beliefs is vital when introducing new concepts to today’s multicultural health care community (55).
Solutions versus Gels versus Foams
Laboratory studies have found that ABHR solutions are more effective than ABHR gels that contain an equivalent concentration of alcohol (22). Usually gels contain approximately 10% less effective alcohol than a similar solution. For example, an ABHR gel containing 60% alcohol has similar effective alcohol activity as a 50% ABHR solution (5). Technically it has proven difficult to develop ABHR gels that contain >70% alcohol without the gel becoming less viscous and more solution-like. Thus the first generations of gel formulations have reduced antimicrobial efficacy compared with solutions (1).
There is some evidence to suggest gels are preferred to solutions, and have a trend towards improved compliance (1)
. Recent evidence suggests that the efficacy of alcohol based gels may depend mainly on concentration and type of alcohol in the formulation, rather than on product consistency (56)
Foams are new to the ABHR market and to date are used less frequently. There is currently minimal clinical evidence available for the use of alcohol based foams. Further clinical tests are encouraged.
HHA recommendations are outlined in the HHA Product Recommendations section, it does not matter if the product chosen is a solution, gel or foam.
ABHR Volume and Drying Time
The volume of hand rub dispensed is important. One mL of alcohol has been shown to be substantially less effective than 3 mL (7). The effective volume of ABHR (2-3 mL; 1-2 squirts from most ABHR dispensers) generally takes 15-20 seconds to dry on hands – hence ABHR drying time is a convenient indicator that sufficient ABHR has been applied. It is important to follow the recommendations of the manufacturer which are usually found on the ABHR bottle.
In clinical practice often smaller volumes are used than what is recommended in the testing of ABHRs. Unless high concentration products are used there is no significant reduction in contaminants with small volumes of ABHR (54).
It is essential that the team in charge of implementing the ABHR educate their staff about the correct use of the product. Specific education is required to ensure the correct dose is administered: it is important to use a two handed action to operate the dispenser, and to recognise that the number of squirts required for the ABHR to be effective may differ between products, or the size of the HCW’s hands. ABHR should never be applied to gloves.
If hands are wet when ABHR is applied
The antimicrobial efficacy of alcohols is very sensitive to dilution with water and is therefore vulnerable to inactivation, especially if only small volumes of ABHR are applied. For instance, if 60% isopropanol were rubbed onto wet hands in two portions of 3 mL (each for 1 minute), the mean log bacterial reduction achieved is 3.7, as compared to 4.3 with dry hands (20). Thus, it is recommended that ABHR be applied to dry hands.
ABHR activity versus other HH antiseptic agents
From: Pittet D, Boyce J. Hand hygiene and patient care: pursuing the Semmelweis legacy. The Lancet Infectious Diseases 2001 April: 9-20