Description of the far-UV-C technology and test room

The far-UV-C technology (Myna Life Technologies, Chesterfield, MO) uses krypton-chloride excimer lamps that emit a primary wavelength of 222 nm with filters to block emitted wavelengths >230 nm. Each device contains 3 lamps with a field of illumination of 60° per lamp. The number of devices required varies with room size; 2 devices are recommended for a typical patient room. The device includes proprietary sensors that detect the presence and location of people relative to the lamps. The device is programmed to automatically reduce or discontinue far-UV-C exposure by turning off 1 or more light modules as needed based on proximity of people to keep exposure below a threshold limit value of 160 mJ/cm² per 8 hours. ^{Reference Blatchley, Brenner and Claus3–Reference Fukui, Niikura and Oda7} This feature is intended to provide maximal far-UV-C doses when people are not present versus in proximity to the devices.

Testing was conducted in a 23.5-m³ room in the research building that was ventilated with ∼4 air changes per hour. Two devices were positioned at opposite corners of one wall 2 m from the floor, angled toward the center of the room, with 1.6 m of space between the devices. A picture of the device and illustration of the test-room setup are included in the Supplementary Material (online). With all 6 lamps from the 2 devices operating, the calculated doses of UV-C delivered over 8 hours at 2 and 3 m from the lamps were 230 and 150 mJ/cm², respectively.

Reduction in aerosolized bacteriophage MS2

For each simulation, an Aerogen Solo (Aerogen, Galway, Ireland) nebulizer was used to release 1 mL aerosol containing 10⁸ plaque-forming units (PFU) of bacteriophage MS2 over 3 minutes. Also, 99% of particles generated by the Aerogen Solo are ≤5 µm diameter. ^{Reference Cadnum, Jencson, Alhmidi, Zabarsky and Donskey8} Air samples were collected using National Institute for Occupational Safety and Health (NIOSH) 2-stage bioaerosol samplers (Tisch Environmental, Cleves, OH) over 5-minute periods at baseline (0–5 minutes after aerosol release) and 5–10, 10–15, 25–30, and 40–45 minutes after release. Bacteriophage MS2 was prepared and quantitatively cultured as previously described. ^{Reference Cadnum, Jencson, Alhmidi, Zabarsky and Donskey8} Each simulation was repeated in triplicate. Log₁₀ reductions were calculated in comparison to control experiments run in the same room with the far-UV-C technology turned off.

Reduction in healthcare-associated pathogens on carriers

We tested the efficacy of the technology against bacteriophage MS2 and several healthcare-associated pathogens using a modification of the American Society for Testing and Materials (ASTM) standard quantitative disk carrier test method (ASTM E 2197-02). ⁹ The healthcare-associated pathogens included a clinical carbapenem-resistant Escherichia coli (CRE) strain, a clinical methicillin-resistant Staphylococcus aureus (MRSA) strain, vancomycin-resistant Enterococcus strain C68, a clinical ribotype 027 Clostridioides difficile strain, and Candida auris strains Antibiotic Resistance Bank (AR)-0381 (clade II; East Asia origin) and AR-0383 (clade III; Africa origin). C. auris AR-0383 forms aggregates and exhibits reduced susceptibility to 254-nm UV-C light in comparison to AR-0381. ^{Reference Pearlmutter, Haq, Cadnum, Jencson, Carlisle and Donskey10}

Testing was conducted in the room previously described with an exposure time of 45 minutes. We used 5% fetal calf serum as a soil load. The 10-µL inoculum of the test organisms was spread to cover the 20-mm steel disks. The disks were oriented horizontally 0.8 m high in the center of the room at 2 m or 3 m from the lamps. Experiments were completed in triplicate. For C. difficile spores, additional experiments were conducted with exposure times of 3 and 5 hours. For MRSA, additional experiments were conducted with the disks placed at the side of the room or on the floor at 2 or 3 m from the nearest lamp. Log₁₀ reductions were calculated in comparison to untreated controls. Disks were processed as previously described. ^{Reference Pearlmutter, Haq, Cadnum, Jencson, Carlisle and Donskey10} A 3-log₁₀ or greater reduction in the test organisms in comparison to untreated controls was considered effective. ^{Reference Pearlmutter, Haq, Cadnum, Jencson, Carlisle and Donskey10}