It is always surprising how much data there is on efficacy of hand rubs and antibacterial soaps, but how little on efficacy of handwashing with soap (HWWS). In setting up the EN 1499 standard test for efficacy of antibacterial soaps, a ring trial was conducted at 15 centres on the efficacy of a 1 min handwash with soft soap, using the generally accepted “standard handwash procedure” and hands contaminated with E. coli. The mean log reduction (LR) on hands was 2.76, although reported values from centres ranged from 2.0 to 3.35 (with one outlier at 4.27)
It is thus interesting to see a new handwashing study by Stephen Luby et al. This was a field trial in Dhaka, Bangladesh among mothers to compare microbial efficacy of soapy water (30 g powdered detergent in 1.5 L water) with bar soap and water alone. Fieldworkers collected hand rinse samples before and after either 1) scrubbing with soapy water for 15 and 30 seconds, 2) scrubbing with bar soap for 15 and 30 seconds, 3) scrubbing with water alone for 15 seconds. Participants were instructed in hand washing technique. Mean LR after HW with washing with soapy water and bar soap for 15 secs was only 0.7 (P < 0.001) for soapy water and 0.6 (p=0.001) for bar soap. Increasing scrubbing time to 30 seconds did not improve removal (P > 0.05). Water alone produced a mean LR 0.3, (P = 0.046) and was less efficacious than soapy water. Although the key finding is that use of soapy water may be appropriate for low-income communities, where there are concerns about the cost of bar soap, the study suggests that efficacy of HWWS with soap for 15-30 secs of “naturally contaminated” under in use conditions may be much less than that achieved in controlled lab panel tests.
The study is at Am. J. Trop. Med. Hyg., 91(2), 2014, pp. 415–423 doi:10.4269/ajtmh.13-0475