The World Health Organization has recognized the shortcomings of current standards for evaluating the in vivo efficacy of hand hygiene products, and has called for methods which are realistic under practical conditions.
Rutter and Macinga (2013) sought to develop a method to evaluate the efficacy of alcohol-based handrubs which reflects the mode of hand contamination typical in healthcare settings to provide an accurate assessment of product performance under in-use conditions.
Stainless steel discs 1 cm in diameter were contaminated with 10 µl of a liquid suspension of S. aureus ATCC 6538 (8 log CFU/ml) and allowed to dry. Discs were stored in a humidity chamber at 50% RH for up to 72 hours prior to use. Hands were contaminated by firmly pressing each fingerpad to a contaminated disc for 2 seconds. Two fingers on each hand were sampled individually by kneading in a neutralizer solution for 30 seconds to obtain pre-treatment counts. A hand hygiene intervention was performed after which the remaining fingers were sampled to obtain post-treatment values. Recovered bacteria were quantified and mean log reductions per finger were calculated.
S. aureus was stable on stainless steel discs for several days. Transfer and recovery of S. aureus from fingers was highly reproducible both between the fingers of individual subjects and between different subjects (mean recovery = 5.9±0.2 log CFU per finger pad; N=65). The organism was stable on the fingers with no die off for at least 40 minutes. A 15 second non-antimicrobial handwash, 0.5 ml, and 1 ml of an alcohol based handrub achieved log reductions of 3.2±0.5, 2.9±1.3 and 3.7±1.0, respectively. Consistent with other hygienic handrub methods, intra-subject variability was low and inter-subject variability was high.
The researchers conclude that contamination of the fingers via contact with a dry surface appears to be a simple and highly reproducible means of evaluating the efficacy of hand hygiene products under practical use conditions. Furthermore, this method utilizes a relevant marker organism, and simulates the primary mode of hand contamination in healthcare settings. Finally, the sampling method may be applied to the clinical setting to perform Phase 3 field studies, to investigate prevention of cross-transmission of pathogens through use of a hygienic handrub.
Reference: Rutter J and Macinga DR. Oral presentation O006 at the 2nd International Conference on Prevention and Infection Control (ICPIC 2013): Development of a method to simulate practical use conditions of hygienic handrubs. Antimicrobial Resistance and Infection Control 2013, 2(Suppl 1):O6 doi:10.1186/2047-2994-2-S1-O6