Effect of moist heat reprocessing of N95 respirators on SARS-CoV-2 inactivation and respirator function

Abstract

BACKGROUND: Unprecedented demand for N95 respirators during the coronavirus disease 2019 (COVID-19) pandemic has led to a global shortage of these masks. We validated a rapidly applicable, low-cost decontamination protocol in compliance with regulatory standards to enable the safe reuse of N95 respirators.

METHODS: We inoculated 4 common models of N95 respirators with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and evaluated viral inactivation after disinfection for 60 minutes at 70°C and 0% relative humidity. Similarly, we evaluated thermal disinfection at 0% to 70% relative humidity for masks inoculated with Escherichia coli. We assessed masks subjected to multiple cycles of thermal disinfection for structural integrity using scanning electron microscopy and for protective functions using standards of the United States National Institute for Occupational Safety and Health for particle filtration efficiency, breathing resistance and respirator fit.

RESULTS: A single heat treatment rendered SARS-CoV-2 undetectable in all mask samples. Compared with untreated inoculated control masks, E. coli cultures at 24 hours were virtually undetectable from masks treated at 70°C and 50% relative humidity (optical density at 600 nm wavelength, 0.02 ± 0.02 v. 2.77 ± 0.09, p < 0.001), but contamination persisted for masks treated at lower relative humidity. After 10 disinfection cycles, masks maintained fibre diameters similar to untreated masks and continued to meet standards for fit, filtration efficiency and breathing resistance.

INTERPRETATION: Thermal disinfection successfully decontaminated N95 respirators without impairing structural integrity or function. This process could be used in hospitals and long-term care facilities with commonly available equipment to mitigate the depletion of N95 masks.

As the coronavirus disease 2019 (COVID-19) pandemic has overwhelmed many health care systems worldwide, the unprecedented demand for personal protective equipment (PPE) has exhausted stockpiles and interrupted global supply chains for N95 respirators. Currently, the proportion of frontline health care workers among individuals infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exceeds 10% in some regions and is expected to increase if PPE stockpiles diminish further.1,2 As a result, protecting front-line workers from SARS-CoV-2 infection is now an immediate global concern.3

Disposable N95 respirators protect users against infectious airborne particles and are therefore critical to front-line workers during the COVID-19 pandemic.3 However, the present global shortage of PPE has forced regulating institutions to adjust infection control measures. Before the pandemic, guidelines recommended disposal of N95 respirators after each patient encounter. Now, evolving guidelines instruct staff to reuse 1 mask over their whole shift, or even longer.4 This policy of reusing disposable masks in the setting of high airborne pathogen exposure — such as aerosol-generating medical procedures in the care of patients with COVID-19 — may result in accumulation of contagious material on the mask surface, risking the health and safety of personnel and patients.5,6 Inactivating accumulated pathogens in disposable respirators without affecting the respirators’ protective properties may enable safe reuse and thus help to alleviate the current global shortage temporarily. However, the sterilization methods regularly used in health care institutions potentially degrade disposable respirators and thereby affect fit or filtration efficiency.7

Thermal disinfection may overcome this issue and provide a widely available and cost-effective decontamination strategy for disposable respirators. Recent reports show a high sensitivity to heat for SARS-CoV-2, as 5 minutes of heating at 70°C inactivates the virus.5,8 The polypropylene microfibres in commercially available N95 respirators have a thermal degradation point above 130°C, suggesting that the filter may withstand repetitive exposure to 70°C.9,10 However, the viricidal efficacy of thermal disinfection for N95 respirators contaminated with SARS-CoV-2, and the protective performance of heat-treated respirators, have not been validated to a level meeting regulatory standards in the United States.

We therefore investigated whether thermal disinfection at 70°C for 60 minutes inactivates pathogens, including SARS-CoV-2, while maintaining critical protective properties of N95 respirators for multiple cycles of disinfection and reuse in a real-world setting.