Last time, we wrote about the two most important standards for testing the efficacy of handrubs; the European CEN EN 1500 and the American ASTM E-1174. Now we summarize the main weaknesses of these standards.
The first issue with the EN 1500 and ASTM E-1174 is the cost. E-1174 needs a minimum of 54 test subjects for the in vivo test and another 54 for the positive control. In the case of EN 1500 the results could be intra-individually compared, thus reduce the sample size at the same statistical power [1].
The required hand treatments are 30 seconds for E-1174 and 30 seconds repeated twice in EN 1500. The actual average duration of a hand hygiene event is less than 15 minutes in most studies [1]. It means that almost no data exists regarding the efficacy values under conditions in which they are actually used. To prove non-inferiority in the efficacy is easier, if we examine longer skin contact. For shorter term, bigger sample size would be required [1].
ASTM E-1174 requires 2 log10 reduction after the 1st use and 3 log10 reduction after the 10th use. The 2 log10 reduction is quite a low requirement that even unmedicated soap and water can fulfil. In health-care settings, strong and immediate effect would be necessary even after the first use [1].
Both EN 1500 and ASTM E-1174 use Escherichia coli for artificial had contamination, and E-1174 allows to substitute E.coli with Serratia marcescens. These organisms are Gram negative bacteria, however Gram positive pathogens, like MRSA and VRE (vancomycin-resistant enterococci) are big threats in hospitals. Goroncy-Bermes 2001 examined the handrub efficacy according to EN 1500 against Micrococcus luteus, as a representative of Gram positive bacteria, and compared it to the efficacy against E.coli. They did not found significant difference, but drew attention to the fact that the ethanol-based handrub (Desderman in their case) was significantly more effective against E.coli than against M. luteus, while there were no significant differences in the case of a propanol-based handrub (Desmanol) [2].
Both standard methods use unrealistic high level hand contamination, which necessitates the use of unrealistic volumes of product at excessive contact times [3]. Microbiological sampling also raises questions, we will discuss it later.
New methods:
ASTM developed new methods in recent years, including ASTM E-2755 (for bacteria-eliminating effectiveness) and ASTM E-2784 (for effectiveness of handwash formulations). Edmonds-Wilson 2015 found that efficacy values are highly depend on the method applied, and efficacy value after the first use was not predictive for the result after the 10th use (see Table 1).
| ASTM method | Mean log10 reduction after the 1st use |
Mean log10 reduction after the 10th use |
| E-1174 | 2.69 ± 0.56 | 4.35 ± 1.38 |
| E-2755 | 3.29 ± 0.94 | 4.06 ± 0.89 |
| E-2784 | 4.57 ± 1.13 | 5.06 ± 0.46 |
Table 1: Effectiveness values of the same handrub measured according to different standards.
Source: Edmonds-Wilson 2015 [4]
These new standards were developed to make the hand contamination procedure more realistic [4]. ASTM E-2755 use Staphilococcus aureus for hand contamination, which is more representative of a hand transmitted pathogen in healthcare environments. It also applies lower level of artificial contamination [3]. A revised version of EN 1500 was released in 2013, which left untouched the key elements of the protocol despite the rising criticism. It may take several years before a new European Norm working group comes up with an alternative recommendation.
Conclusion:
An ideal efficacy test of handrubs should focus on the condition used in healthcare settings; about 15 second application time, single use, and on germs representing well the typical pathogens in health-care setting. It should be carried out cost-effectively, to facilitate the development of new formulations. Such a new, internationally accepted standard would be a huge step-forward. Until then, keep in mind that different standards result different efficacy values, and try to choose a product that is tested with different test methods.