Test organisms

The test organisms included a clinical isolate of pulsed-field gel electrophoresis type USA800 methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE) strain C68, bacteriophage MS2, and Clostridioides difficile American type culture collection strain 43598. C. difficile spores and bacteriophage MS2 were prepared and quantitatively cultured as previously described. ^{Reference Cadnum, Li, Redmond, John, Pearlmutter and Donskey3,Reference Cadnum, Jencson and Gestrich4}

Description of the mobile disinfection cabinet

The PURitALL 3030L high-level disinfection cabinet is a mobile wheeled unit intended for disinfection of noncritical medical devices, packaged supplies, personal protective equipment (PPE), and personal items, including electronics. The unit has 2 doors, one for loading items and the other for unloading processed items. The doors lock automatically prior to cycle startup. The outer dimensions of the device are 182 cm (height), 76 cm (width), and 76 cm (depth); the dimensions of the inner disinfection chamber are 142 cm (height), 68 cm (width) and 68 cm (depth). The cabinet has plastic racks used to hold or hang items in a manner that maximizes exposure to UV-C light. The Supplementary Material (online) includes pictures of the device.

The device provides a single cycle time of ∼15 minutes incorporating 254 nm UV-C light and aerosolized 3%–7% hydrogen peroxide. For the tests performed, the concentration of hydrogen peroxide was 6%. Additional features intended to enhance antimicrobial activity of the device include heat to a peak temperature of 35–50ºC and high surface air flow to facilitate even distribution of the aerosolized hydrogen peroxide and to dry items after cycle completion. Hydrogen peroxide is converted to water and oxygen prior to cycle completion. According to the manufacturer, the door can be opened safely immediately after cycle completion. According to the manufacturer, the 15-minute cycle time was chosen based on efficacy testing.

Efficacy of the disinfection cabinet against the test organisms on real-world items

Testing was performed using a modification of the American Society for Testing and Materials (ASTM) standard quantitative disk-carrier test method (ASTM E 2197). ⁵ The inoculum in 5% fetal calf serum was spread on the test items to cover ∼1 cm ^{Reference Mathew, Cadnum, Sankar, Jencson, Kundrapu and Donskey2} and allowed to air dry. The inoculated items included a stethoscope (diaphragm inoculated), cell phone, and inside and outside surfaces of a surgical mask and blood pressure cuff. The items were distributed in multiple locations throughout the chamber. The surgical mask and blood pressure cuff were hung from a rack in a manner that maximized UV-C light exposure. After completion of a 15-minute cycle, the inoculum sites were sampled with rayon swabs moistened with Dey-Engley neutralizer and processed as previously described. ^{Reference Cadnum, Li, Redmond, John, Pearlmutter and Donskey3,Reference Cadnum, Jencson and Gestrich4} To assess how much benefit the aerosolized hydrogen peroxide added to UV-C alone, experiments were run both with and without hydrogen peroxide (ie, water was substituted for hydrogen peroxide).

For bacteriophage MS2, additional experiments were conducted with items routinely used in our facility during care of patients with coronavirus disease 2019 (COVID-19), including powered air-purifying respirator (PAPR) helmet and face shield, goggles, and face shield. The experiments were conducted both with and without hydrogen peroxide.

Log₁₀ reductions were calculated by subtracting viable organisms recovered from treated versus untreated control items inoculated using the same method. All experiments were performed in triplicate. A 3 log₁₀ or greater reduction in the test organisms in comparison to untreated controls was considered effective. ^{Reference Cadnum, Li, Redmond, John, Pearlmutter and Donskey3,Reference Cadnum, Jencson and Gestrich4}