Comparative in vivo efficiencies of hand-washing agents against hepatitis A virus (HM-175) and poliovirus type 1 (Sabin)

Abstract

The abilities of 10 hygienic hand-washing agents and tap water (containing approximately 0.5 ppm of free chlorine) to eliminate strain HM-175 of hepatitis A virus (HAV) and poliovirus (PV) type 1 (Sabin) were compared by using finger pad and whole-hand protocols with three adult volunteers. A mixture of the two viruses was prepared in a 10% suspension of feces, and 10 μl of the mixture was placed on each finger pad. The inoculum was allowed to dry for 20 min, and the contaminated area was exposed to a hand-washing agent for 10 s, rinsed in tap water, and dried with a paper towel. In the whole- hand protocol, the hands were contaminated with 0.5 ml of the virus mixture, exposed for 10 s to a hand-washing agent, washed, and dried as described above. Tryptose phosphate broth was used to elute any virus remaining on the finger pads or hands. One part of the eluate was assayed directly for PV with FRhK-4 cells, while the other part was first treated with a PV-neutralizing serum and then assayed for HAV with the same cell line. The results are reported as mean percentages of reduction in PFU compared with the amount of infectious virus detectable after initial drying. In the finger pad protocol, an unmedicated liquid soap was the least effective agent (77.96% ± 7.17% reduction) for removing HAV, and a medicated liquid soap was the most effective agent (92.04% ± 4.02% reduction) for reducing the HAV titer; the smallest reduction in PV titer was obtained with tap water (85.22% ± 2.91% reduction), and the same medicated soap was the most effective agent against PV (98.39% ± 1.98% reduction). Significant differences were found between HAV removal and PV removal with 9 of the 11 agents tested (F = 102.14; P < 0.05). There was good correspondence between the results of the finger pad protocol and the results of the whole-hand method. In additional experiments, we attempted to transfer infectious virus remaining on finger pads treated with various hand-washing agents by having the finger pads contact clean metal disks at a pressure of about 1 kg/cm2 for 10 s. Detectable amounts of both of the viruses were transferred after washing with all of the agents except a 1:30 dilution of a mixture containing 1.5% chlorhexidine gluconate and 15% cetrimide in 70% ethanol, 70% ethanol alone, and a foam containing 62% ethanol. More work is needed to determine the health implications of residual infectious viruses on washed hands, but our findings reinforce the need to determine the virus-eliminating efficiencies of hand-washing products, particularly those used in health care settings, day-care centers, and food establishments.