Effectiveness of Ultraviolet-C Light and a High-Level Disinfection Cabinet for Decontamination of N95 Respirators

Abstract

Background: Shortages of personal protective equipment (PPE) including N95 respirators are an urgent concern in the setting of the global COVID-19 pandemic. Decontamination of PPE could be useful to maintain adequate supplies, but there is uncertainty regarding the efficacy of decontamination technologies.

Methods: A modification of the American Society for Testing and Materials standard quantitative carrier disk test method (ASTM E-2197-11) was used to examine the effectiveness of 3 methods, including ultraviolet-C (UV-C) light, a high-level disinfection cabinet that generates aerosolized peracetic acid and hydrogen peroxide, and dry heat at 70°C for 30 minutes. We assessed the decontamination of 3 commercial N95 respirators inoculated with methicillin-resistant Staphylococcus aureus (MRSA) and bacteriophages MS2 and Phi6; the latter is an enveloped RNA virus used as a surrogate for coronaviruses. Three and 6 log₁₀ reductions on respirators were considered effective for decontamination and disinfection, respectively.

Results: UV-C administered as a 1-minute cycle in a UV-C box or a 30-minute cycle by a room decontamination device reduced contamination but did not meet criteria for decontamination of the viruses from all sites on the N95s. The high-level disinfection cabinet was effective for decontamination of the N95s and achieved disinfection with an extended 31-minute cycle. Dry heat at 70°C for 30 minutes was not effective for decontamination of the bacteriophages.

Conclusions: UV-C could be useful to reduce contamination on N95 respirators. However, the UV-C technologies studied did not meet pre-established criteria for decontamination under the test conditions used. The high-level disinfection cabinet was more effective and met criteria for disinfection with an extended cycle.

Keywords: N95 respirator; SARS-CoV-2; Ultraviolet-C; decontamination; peracetic acid.

Figure 1.

Pictures of the 3 N95 respirators evaluated in the study and areas where the test organisms were applied.

Figure 2.

Efficacy of ultraviolet-C (UV-C) light for decontamination of methicillin-resistant Staphylococcus aureus (MRSA), bacteriophage MS2, and bacteriophage Phi6 on 3 different N95 respirators (3M 1860S, Moldex 1517, and Kimberly-Clark 46727). Aliquots of 10 μL containing 10⁶ colony-forming units (CFU) or plaque-forming units (PFU) of the test organisms in the simulated mucus suspension were spread to cover an area of 1 cm² on 3 different areas on the respirator surface (top exterior, edge exterior, and interior) as shown in Figure 1. The respirators were exposed to a 60-second cycle of UV-C inside a UV-C box. Error bars indicate standard error.

Figure 3.

Efficacy of ultraviolet (UV) light delivered by low-pressure mercury decontamination device for decontamination of methicillin-resistant Staphylococcus aureus (MRSA), bacteriophage MS2, and bacteriophage Phi6 on Moldex 1517 N95 respirators. 10-μL aliquots containing 10^>6 colony-forming units (CFU) or plaque-forming units (PFU) of the test organisms in the simulated mucous suspension were spread to cover an area of 1-cm2 on 3 different areas on the respirator surface (top exterior, edge exterior, and interior) as shown in Figure 1. The respirator was exposed to a 15-minute cycle of UV at 3 feet from the bulbs then turned for another 15-minute cycle on the opposite side. Error bars indicate standard error.

Figure 4.

Pictures showing colorimetric indicators placed adjacent to respirators during ultraviolet-C cycles.

Figure 5.

Efficacy of a multi-purpose high-level disinfection cabinet for decontamination or disinfection of methicillin-resistant Staphylococcus aureus (MRSA) and bacteriophage MS2 on N95 respirators. 10-μL aliquots containing 10⁶ colony-forming units (CFU) or plaque-forming units (PFU) of the test organisms in the simulated mucous suspension were spread to cover an area of 1-cm² on 3 different areas on the respirator surface (top exterior, edge exterior, and interior) as shown in Figure 1. The respirator was exposed to 1, 2, or 3 22-minute treatment cycles or a single extended cycle of 31 minutes. Error bars indicate standard error.