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

Abstract

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 log(10) CFU/ml of Serratia marcescens, an average of 5.28 log(10) CFU remained on each hand after washing, and 2.23 log(10) 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 log(10) 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 log(10) 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 log(10) CFU) was significantly lower than the mean number after washing with contaminated bulk-soap-refillable dispensers (0.74 log(10) CFU; P < 0.01). Finally, significantly higher levels of Gram-negative bacteria were recovered from students (2.82 log(10) CFU per hand) than were recovered from staff (2.22 log(10) CFU per hand) after washing with contaminated bulk soap (P < 0.01). These results demonstrate that washing with contaminated soap from bulk-soap-refillable dispensers can increase the number of opportunistic pathogens on the hands and may play a role in the transmission of bacteria in public settings.

Fig. 1.

Sample images from a controlled study (Table 2) to determine the number of bacteria from contaminated hands transferred to an agar surface before (A and C) and after (B and D) hand washing with soap containing 4.51 log₁₀ CFU/ml (A and B) or 7.51 log₁₀ CFU/ml (C and D) of S. marcescens.

Fig. 2.

Log₁₀ CFU change in Gram-negative bacteria recovered from hands of elementary school students and staff as a result of hand washing with contaminated soap (solid bars) versus uncontaminated control soaps (open bars).

Fig. 3.

Gram-negative bacteria recovered from the hands of elementary school students and staff before and after washing with contaminated bulk soap. Fourteen contaminated soap dispensers and 2 uncontaminated soap controls were used by students and staff. n = 4 for dispensers 2 to 5 and 12, and n = 2 for dispenser 10; n = 5 for all other dispensers. *, P < 0.05 for bacteria recovered per hand before versus after hand washing by paired two-sample t test.