Abstract
The handwashing literature, while extensive, often contains conflicting data and key variables are understudied or not studied at all. Some handwashing recommendations are made without scientific support, and there is limited agreement between recommendations. The influence of key variables including soap volume, lather time, water temperature, and product formulation on hand wash efficacy was investigated. Baseline conditions were 1 mL of a bland (nonantimicrobial) soap, a 5 s lather time, and 38 °C (100 °F) water temperature. A nonpathogenic strain of Escherichia coli ATCC 11229 served as the challenge microorganism. Twenty volunteers (10 men, 10 women) participated in the study and each test condition had 20 replicates. An antimicrobial soap formulation (1% chloroxylenol, or PCMX) was not significantly different from the bland soap at removing E. coli under a variety of test conditions. Overall, the antimicrobial soap used in this study had a mean 1.94 log CFU reduction (range 1.83 to 2.10 mean log reduction), and bland soap had a mean 2.22 log CFU reduction (range 1.91 to 2.54 mean log CFU reduction). Overall, lather time did significantly influence efficacy in one scenario, in which a 0.5 greater log reduction was observed for a 20 s with bland soap compared to the baseline wash (P=0.020). Water temperature as high as 38°C (100°F) vs. a low of 15°C (60°F) did not have a significant effect on the reduction of bacteria during hand washing, however this resulted in an energy usage difference between the temperatures. No significant differences were observed between mean log reductions of men and women (men= 2.08 mean log reduction, women=2.08 mean log reduction, P=0.988). A large part of the variability in the data observed was between the volunteers. Understanding what behaviors and human factors influence hand washes the most may help future studies find which techniques can optimize the effectiveness of a hand wash.