Contaminated sink drains and other wastewater drainage sites have been linked to outbreaks of infections with gram-negative bacilli. ^{Reference Volling, Ahangari and Bartoszko1} Organisms colonizing sink drains can be dispersed from beneath the strainer to the bowl, countertop, and to patients or personnel. ^{Reference Dandalides, Rutala and Sarubbi2–Reference Hajar, Mana, Cadnum and Donskey4} Thus, there is a need for effective strategies to reduce sink drain colonization. Pouring disinfectants into sinks has only a modest, transient effect because the disinfectants flow rapidly down the drain, providing inadequate contact time and poor penetration into areas harboring biofilm-associated organisms. ^{Reference Cadnum, Livingston, Gestrich, Jencson, Wilson and Donskey5,Reference Jones, Mana and Cadnum6}

Recently, a foam application of a 3.13% hydrogen peroxide and 0.05% peracetic acid disinfectant (Virasept, Ecolab, Saint Paul, MN) has been shown to suppress sink drain colonization significantly longer than poured liquid disinfectants, presumably due to enhanced contact time and penetration into biofilm. ^{Reference Jones, Mana, Cadnum, Jencson, Silva, Wilson and Donskey7,Reference Ramos-Castaneda, Faron and Hyke8} The foam product is Environmental Protection Agency (EPA)-registered to kill Pseudomonas aeruginosa and Staphylococcus aureus biofilms with a 5-minute contact time. However, the optimal frequency of application is uncertain. Based on a single application of the foam disinfectant, Ramos-Castaneda et al. ^{Reference Ramos-Castaneda, Faron and Hyke8} proposed that drain disinfection every 3–5 days might be effective. Jones et al. ^{Reference Jones, Mana, Cadnum, Jencson, Silva, Wilson and Donskey7} suggested that drain disinfection every 3 days might be effective and noted a progressive decrease in the bacterial burden with repeated treatments every 3 days. Here, we examined the impact of different frequencies of foam disinfectant application on the burden of gram-negative bacilli in hospital sink drains.

The study was conducted on medical-surgical wards at the Cleveland VA Medical Center. Twenty-four sinks in patient rooms or bathrooms were randomized (6 per group) to receive foam disinfection with Virasept at different intervals, including daily, every second day, every third day, or every fifth day. At baseline, all drains were colonized with P. aeruginosa with ∼5–7 log₁₀ colony-forming units (CFU) per swab; P. aeruginosa is the predominant organism colonizing more than 95% of sinks in the hospital. The foam was generated from ∼50 mL of the disinfectant and was allowed to dwell for 5 minutes before flushing with water.

ESwabs (Becton Dickinson, Sparks, MD) were used to sample the drain to a depth of 2.4 cm below the strainer prior to the intervention and then daily for 14 days; swabs were collected immediately prior to foam application on days of sink treatment. The swabs were processed to quantify total gram-negative bacilli. ^{Reference Jones, Mana, Cadnum, Jencson, Silva, Wilson and Donskey7} The level of reduction in drain colonization required to minimize risk for dispersal of bacteria is uncertain; for the purposes of this study, a reduction to 2 log₁₀ CFU that was sustained for 2 or more treatments was deemed effective.

Based on the initial results, we hypothesized every third-day treatment might be effective in maintaining a sink drain concentration of <2 log₁₀ CFU of gram-negative bacilli if the burden was first reduced by applying foam daily for several days. Therefore, we treated 11 additional sinks colonized with P. aeruginosa with foam daily for 4 days followed by every third-day application for 4 treatments (N = 7 sinks) or no further foam application (N = 4 control sinks).

Figure 1(a) shows the effect of repeated foam application on the burden of gram-negative bacilli. The concentration of gram-negative bacilli was reduced to ≤2.2 log₁₀ CFU 1 day after each application. However, sustained reductions to less than 2 log₁₀ CFU within 2–3 days were only achieved in the daily application group. With every second-day application, the concentration of gram-negative bacilli trended downward and remained below 2 log₁₀ CFU after the sixth and seventh applications.

Figure 1. Effect of different frequencies of foam disinfectant applications on the burden of gram-negative bacilli recovered from sink drains colonized with Pseudomonas aeruginosa. (a). Sinks (6 per group) received foam disinfection daily, every second day, every third day, or every fifth day. (b). Sinks (N = 11) received foam disinfection daily for 4 days followed by every third day for 4 treatments (N = 7 sinks) or no further foam application (N = 4 sinks). *, foam application.

Note. CFU, colony-forming unit. Error bars indicate standard error.

Figure 1(b) shows the impact of daily foam application for 4 days followed by every third-day application versus no further foam application. Daily foam application reduced the concentration of gram-negative bacilli to 2 log₁₀ CFU. However, the concentrations of gram-negative bacilli increased to above 2 log₁₀ CFU during subsequent every third-day applications and returned to baseline in control sinks that did not receive further foam applications.

In response to outbreaks linked to sinks, it has been recommended that facilities consider disinfection of sink drains using an EPA-registered disinfectant with claims against biofilms in consultation with state or local public health departments. ^{Reference Glowicz, Landon and Sickbert-Bennett9} Previous studies have demonstrated that the EPA-registered hydrogen peroxide and peracetic acid disinfectant administered as foam can suppress drain contamination. ^{Reference Jones, Mana, Cadnum, Jencson, Silva, Wilson and Donskey7,Reference Ramos-Castaneda, Faron and Hyke8} Our findings suggest that daily application may be required to achieve a rapid and consistent reduction in colonization. Application of the foam disinfectant every 2 days resulted in a downward trend in drain contamination, but suppression to below 2 log₁₀ CFU only occurred after the sixth application.

Our study has some limitations. Testing was conducted in one facility and all sinks were colonized with P. aeruginosa. Additional studies are needed in other facilities and for sinks colonized with carbapenem-resistant Enterobacterales which have been associated with many outbreaks linked to sinks. ^{Reference Volling, Ahangari and Bartoszko1} We tested a single 5-minute daily application of the foam as recommended by the manufacturer. It is possible that longer exposure times might have greater efficacy. A reduction to 2 log₁₀ CFU was deemed effective. However, the level of reduction required to minimize the risk of dispersal of organisms is uncertain. We did not detect any obvious adverse effects of repeated foam application on the sinks. However, additional studies are needed as the duration of treatment was relatively short. We did not perform a cost analysis but estimated that the cost of the disinfectant for each application was <$2.00. Finally, studies are needed to determine if application of the foaming disinfectant will be effective in controlling outbreaks linked to sink colonization.