Bacterial hand contamination and transfer after use of contaminated bulk-soap-refillable dispensers

Bulk-soap-refillable dispensers are prone to extrinsic bacterial contamination, and recent studies demonstrated that approximately one in four dispensers in public restrooms are contaminated. The purpose of this study was to quantify bacterial hand contamination and transfer after use of contaminated soap under controlled laboratory and in-use conditions in a community setting. Under laboratory conditions using liquid soap experimentally contaminated with 7.51 log₁₀ CFU/ml of Serratia marcescens, an average of 5.28 log₁₀ CFU remained on each hand after washing, and 2.23 log₁₀ CFU was transferred to an agar surface. In an elementary-school-based field study, Gram-negative bacteria on the hands of students and staff increased by 1.42 log₁₀ CFU per hand (26-fold) after washing with soap from contaminated bulk-soap-refillable dispensers. In contrast, washing with soap from dispensers with sealed refills significantly reduced bacteria on hands by 0.30 log₁₀ CFU per hand (2-fold). Additionally, the mean number of Gram-negative bacteria transferred to surfaces after washing with soap from dispensers with sealed-soap refills (0.06 log₁₀ CFU) was significantly lower than the mean number after washing with contaminated bulk-soap-refillable dispensers (0.74 log₁₀ CFU; P < 0.01). Finally, significantly higher levels of Gram-negative bacteria were recovered from students (2.82 log₁₀ CFU per hand) than were recovered from staff (2.22 log₁₀ CFU per hand) after washing with contaminated bulk soap (P < 0.01). These results demonstrate that washing with contaminated soap from bulk-soaprefillable dispensers can increase the number of opportunistic pathogens on the hands and may play a role in the transmission of bacteria in public settings.