Researchers Test Influence of Volume on Hand Coverage and Bactericidal Efficacy in Hand Disinfection

Some manufacturers recommend using 1.1 mL per application of alcohol-based handrubs for effective hand disinfection; however, whether this volume is sufficient to cover both hands, as recommended by the World Health Organization, and fulfills current efficacy standards, is unknown. A study by Kampf, et al. (2013) aimed to determine hand coverage for three handrubs (two gels based on 70 percent v/v and 85 percent w/w ethanol and a foam based on 70 percent v/v ethanol) applied at various volumes.
 
Products were tested at product volumes of 1.1 mL, 2 mL, 2.4 mL as well as one- and two-pump dispenser pushes; the foam product was tested in addition at foam volumes of 1.1 mL, 2 mL, and 2.4 mL. Products were supplemented with a fluorescent dye and 15 participants applied products using responsible application techniques without any specific steps but the aim of completely covering both hands. Coverage quality was determined under ultraviolet light by two blinded investigators. Efficacy of the three handrubs was determined according to ASTM E 1174-06 and ASTM E 2755-10. For each experiment, the hands of 12 participants were contaminated with Serratia marcescens and the products applied as recommended (1.1 mL for 70 percent v/v ethanol products; 2 mL for the 85 percent w/w ethanol product). Log10-reduction was calculated.
 
The researchers found that volumes < 2 mL yielded high rates of incomplete coverage (67 percent to 87 percent) whereas volumes >= 2 mL gave lower rates (13 percent to 53 percent). Differences in coverage were significant between the five volumes tested for all handrubs (p < 0.001; two-way ANOVA) but not between the three handrubs themselves (p = 0.796). Application of 1.1 mL of 70 percent v/v ethanol rubs reduced contamination by 1.85 log10 or 1.60 log10 (ASTM E 1174-06); this failed the US FDA efficacy requirement of at least 2 log10. Application of 2 mL of the 85 percent w/w ethanol rub reduced contamination by 2.06 log10 (ASTM E 1174-06), fulfilling the FDA efficacy requirement. Similar results were obtained according to ASTM E 2755-10.

The researchers concluded that their data indicated that handrubs based on 70 percent ethanol (v/v) with a recommended volume of 1.1 mL per application do not ensure complete coverage of both hands and do not achieve current ASTM efficacy standards. Their research was published in BMC Infectious Diseases.

Reference: Kampf G, Ruselack S, Eggerstedt S, Nowak N and Bashir M. Less and less--influence of volume on hand coverage and bactericidal efficacy in hand disinfection. BMC Infectious Diseases 2013, 13:472 doi:10.1186/1471-2334-13-472