Quest for a realistic in vivo test method for antimicrobial hand-rub agents: introduction of a low-volume hand contamination procedure.

A novel method has been developed for the evaluation of alcohol-based hand rubs (ABHR) that employs a hand contamination procedure that more closely simulates the in-use conditions of ABHR. Hands of human subjects were contaminated with 0.2 ml of a concentrated suspension of Serratia marcescens (ATCC 14756) to achieve baseline contamination between 8 and 9 log₁₀ CFU/hand while allowing product to be applied to dry hands with minimal soil load. Evaluation of 1.5 ml of an ABHR gel containing 62% ethanol produced log₁₀ reductions of 2.66 ± 0.96, 2.40 ± 0.50, 2.41 ± 0.61, and 2.33 ± 0.49 (means ± standard deviations) after 1, 3, 7, and 10 successive contamination/product application cycles. In a study comparing this low-volume contamination (LVC) method to ASTM E1174, product dry times were more realistic and log₁₀ reductions achieved by the ABHR were significantly greater when LVC was employed (P < 0.05). These results indicate that a novel low-volume hand contamination procedure, which more closely represents ABHR use conditions, provides more realistic estimates of in-use ABHR efficacies. Based on the LVC method, log₁₀ reductions produced by ABHR were strongly dependent on the test product application volume (P < 0.0001) but were not influenced by the alcohol concentration when it was within the range of 62 to 85% (P = 0.378).