Evolving the EN 1500 test method for alcohol-based hand rub closer to clinical reality by reducing the organic load on hands and enabling product to be applied to dry hands

Background: The methods currently used in Europe and North America to evaluate the bactericidal efficacy of hand hygiene products have some limitations (e.g. selection of test organism, method of contamination), and none of the methods allow prediction of actual clinical efficacy. Therefore, the World Health Organization has proposed the development of methods that better reflect typical clinical reality.

Methods: In Experiment 1, two contamination methods (immersion method according to EN 1500 and low-volume method according to ASTM E2755) were tested with the EN 1500 test organism Escherichia coli using 60% v/v iso-propanol. Experiment 2 compared the two contamination methods with Enterococcus faecalis. Experiment 3 compared the two test organisms using the low-volume contamination method. Data within each experiment were compared using the Wilcoxon test for paired samples, and data from all experiments were combined and fit to linear mixed-effects models.

Results: Mixed-effects analysis confirmed that both the test organism and the contamination method impacted the pre-values, and all three factors influenced log₁₀ reductions. Higher pre-values resulted in significantly higher log₁₀ reductions, immersion contributed to significantly higher log₁₀ reductions, and E. coli showed significantly lower log₁₀ reductions.

Conclusion: An efficacy evaluation against E. faecalis with a low-volume contamination method could be considered as an alternative to the EN 1500 standard. This could help to improve the clinical relevance of the test method by including a Gram-positive organism and reducing the soil load, allowing product application closer to reality.