Quantity of soap as a variable in handwashing.

The purposes of this study were to assess the effect of two quantities (1 mL or 3 mL) of four different handwashing products on reductions in log colony-forming units (CFU) from the hands and to determine the amount of liquid soap used for handwashing by personnel in one hospital. First, 40 subjects were assigned by block randomization to one of four handwashing products (4% chlorhexidine gluconate in a detergent base, two alcohol hand rinses, and a liquid, nonantimicrobial soap) to be used in either 1 mL or 3 mL amounts per wash. Each subject washed his or her hands 15 times per day for five days. After one and five days of handwashing there were significant reductions over baseline in log CFU between handwashing products (P less than 0.001). Additionally, subjects using 3 mL of antiseptic soap had significantly greater reductions in log CFU than those using 1 mL (P less than 0.001). Among subjects using control liquid soap there was no such dose response. Second, a survey of 47 members of a hospital nursing staff from nine specialty areas and ten individuals in the general population was conducted to measure amounts of two liquid soaps used for handwashing. Amount of soap ranged from 0.4 to 9 mL per handwash. Personnel working in clinical areas where patients were at high risk for nosocomial infection used significantly more soap than did others (P less than 0.05). We conclude that quantity of soap used for handwashing is one variable influencing the microbial counts on hands, and that the quantity of soap used by health care personnel varies considerably.