key: cord-265233-v5sq5epy
authors: Cassorla, Lydia
title: Decontamination and Reuse of N95 Filtering Facepiece Respirators: Where Do We Stand?
date: 2020-10-15
journal: Anesth Analg
DOI: 10.1213/ane.0000000000005254
sha: 
doc_id: 265233
cord_uid: v5sq5epy

The coronavirus disease 2019(COVID-19) pandemic created an extraordinary demand for N95 and similarly rated filtering facepiece respirators (FFR) that remain unmet due to limited stock, production constraints, and logistics. Interest in decontamination and reuse of FFR, a product class designed for single use in health care settings, has undergone a parallel surge due to shortages. A worthwhile decontamination method must provide effective inactivation of the targeted pathogen(s), and preserve particle filtration, mask fit, and safety for a subsequent user. This discussion reviews the background of the current shortage, classification, structure, and functional aspects of FFR, and potentially effective decontamination methods along with reference websites for those seeking updated information and guidance. The most promising techniques utilize heat, hydrogen peroxide, microwave-generated steam, or ultraviolet light. Many require special or repurposed equipment and a detailed operational roadmap specific to each setting. While limited, research is growing. There is significant variation between models with regard to the ability to withstand decontamination yet remain protective. The number of times an individual respirator can be reused is often limited by its ability to maintain a tight fit after multiple uses rather than by the decontamination method itself. There is no single solution for all settings; each individual or institution must choose according to their need, capability, and available resources. As the current pandemic is expected to continue for months to years, and the possibility of future airborne biologic threats persists, the need for plentiful, effective respiratory protection is stimulating research and innovation.

P ersistent shortages of filtering facepiece respirators (FFR) to protect health care workers (HCW) 1 during the current coronavirus disease 2019 (COVID-19) pandemic 2,3 has driven interest in decontamination and reuse. Where do we stand with regard to its efficacy, safety, and role?

Use of a new, well-fitting N95 FFR has an established safety record that is lacking for decontaminated respirators; therefore, decontamination and reuse remain a crisis management strategy to be considered when conservation strategies including extended use have been exhausted. [4] [5] [6] This review of decontamination methods compliments Nathan's infographic Waste Not, Want Not 7 with background to the FFR shortage, a review of available literature, updated recommendations, and links to websites expected to contain future guidance. Knowledge is growing as relevant studies emerge. Consequently, several preprint reports of potential interest that have not yet benefitted from a peer-review process are included with

The coronavirus disease 2019 (COVID-19) pandemic created an extraordinary demand for N95 and similarly rated filtering facepiece respirators (FFR) that remain unmet due to limited stock, production constraints, and logistics. Interest in decontamination and reuse of FFR, a product class designed for single use in health care settings, has undergone a parallel surge due to shortages. A worthwhile decontamination method must provide effective inactivation of the targeted pathogen(s), and preserve particle filtration, mask fit, and safety for a subsequent user. This discussion reviews the background of the current shortage, classification, structure, and functional aspects of FFR, and potentially effective decontamination methods along with reference websites for those seeking updated information and guidance. The most promising techniques utilize heat, hydrogen peroxide, microwave-generated steam, or ultraviolet light. Many require special or repurposed equipment and a detailed operational roadmap specific to each setting. While limited, research is growing. There is significant variation between models with regard to the ability to withstand decontamination yet remain protective. The number of times an individual respirator can be reused is often limited by its ability to maintain a tight fit after multiple uses rather than by the decontamination method itself. There is no single solution for all settings; each individual or institution must choose according to their need, capability, and available resources. As the current pandemic is expected to continue for months to years, and the possibility of future airborne biologic threats persists, the need for plentiful, effective respiratory protection is stimulating research and innovation. (Anesth Analg XXX;XXX:00-00) BACKGROUND N95 FFR play an established role to protect HCW from airborne transmission of infection. 8 While FFR are not superior to surgical masks for protection of HCW from seasonal flu, [9] [10] [11] [12] [13] [14] retrospective studies showed increased protection from severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1). [15] [16] [17] [18] [19] Infectious droplets and aerosols are considered a primary transmission mechanism of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of COVID-19 illness, [20] [21] [22] and data indicate greater resilience in aerosols than SARS-CoV-1. 23 Centers for Disease Control and Prevention (CDC) guidance recommends N95 FFR or higher level respiratory protection in multiple settings for HCW treating potential COVID-19 patients. 24 A recent meta-analysis supported an association between FFR and protection from coronaviruses including SARS-CoV-2. 25 Universal masking in a major US health care system was associated with reduced HCW infections. 26 Peer-reviewed research comparing the risks and benefits of recycled to single-use FFR is lacking; however, persistent widespread shortages have changed practices. 27 Logistics, hoarding, price gouging, theft, faulty or nonexistent products, and fears of government diversion have exacerbated intense competition for new FFR. [28] [29] [30] [31] [32] [33] [34] In 2006, the Institute of Medicine, now the National Academy of Medicine, convened a "Committee on the Development of Reusable Facemasks for Use during an Influenza Pandemic." Highlighting unpreparedness, 2 reports recommended "expeditious research and policy action" to develop personal protective equipment (PPE) designed to withstand decontamination, evidence-based performance standards, and improved coordination among regulatory agencies. 9, 35 Multiple government-funded studies of FFR decontamination followed without establishing a scalable, evidence-based solution. 4, [36] [37] [38] [39] [40] [41] [42] [43] A 2019 report to the Federal Drug Administration (FDA) concluded, "There is a need for N95 respirators designed for hospital decontamination and reuse to meet the needs of HCW." 39

Science to guide N95 FFR decontamination is scarce due to longstanding government and manufacturer recommendations for disposal following single use. [43] [44] [45] There is however a current surge. Table 1 contains websites selected as likely sources of relevant future information and guidance. They are hosted by the CDC, 5 

A worthy decontamination method must effectively inactivate the target pathogen(s) without impairing particle filtration, effective fit, or safety to a subsequent user. 35 Microorganisms have varied resistance to decontamination (≥3-log reduction; 99.9% inactivated) and sterilization (≥6-log reduction; 99.9999% inactivated). 49 Enveloped viruses including coronaviruses are among the most susceptible. Prions and spores are most resistant. 49 Few FFR decontamination efficacy studies have used SARS-CoV-2. Access to biosafety level-3 (BSL-3) laboratories with appropriate protocols and worker protections is required. 50 Most measured inactivation of surrogate organisms, including spores, bacteria, SARS-CoV-1, and flu viruses. Thus far, susceptibility of SARS-CoV-2 appears similar to other single-stranded RNA coronaviruses including SARS-CoV-1. 51, 52 Laboratory conditions may not readily replicate real-world factors. Multiple studies report that germicidal efficacy of several methods varies substantially depending on the contaminant's solution or medium type and protein content. 53-57 SARS-CoV-1 and SARS-CoV-2 also have variable durability in different human fluids, 58 and on different surface types, 52,59 highlighting the value of studies measuring decontamination of FFR fabric.

The best-supported methods involve heat, hydrogen peroxide (HP), microwave-generated steam (MWGS), or ultraviolet (UV) light (Table 2) .

Many others are discouraged. Gamma irradiation 94 and standard liquid antiseptics including soap and water, ethanol, povidone-iodine, chlorhexidine, and benzalkonium chloride damage FFR electret and/or filter function. 54, 59 Household bleach leaves a persistent strong odor. 36, 37, 61, 62, 76, 77 Ethylene oxide (EtO) is neurotoxic, carcinogenic, and teratogenic and not recommended due to potential residue. 6, 36, 48, 61, 78, 85 Decontamination Methods Time: How Long for SARS-CoV-2? The simplest method to decontaminate FFR is enough time for the contaminant to die. Decay is most rapid in the first hours and speeded with increased temperature (T). Surface type or medium and relative humidity (RH) are important factors. 52, [58] [59] [60] [61] 63, 94 The number of days until viable SARS-CoV-2 is undetectable at 22 °C with ~65% RH is 2 on cloth, 3-5 on glass, and 7 on stainless steel (SS) or plastic. 59, 60, 63 Detectable amounts persist after 7 days on a surgical mask, 59 7 days in solution, 63 and 14 days in culture medium. 59 Shorter surface viability times were reported by Fischer et al 52 who measured data and created a model for expected SARS-CoV-2 decay. On N95 fabric, 3-log reduction at 22 °C required 13 hours, and 6-log reduction required 26 hours. 52 Intermediate RH speeds decay of viral aerosols. 94 T <22 °C will help preserve the virus. 52, 59, 60 Before considering decontamination and reuse, the CDC currently recommends each HCW be issued 5 FFR, and store each ≥5 days before reuse. 6 To date, there are no definitive studies of viability of SARS-CoV-2 at room T on any specific N95 respirator model. Adequate stock, and clean, dry storage are required for a time-based strategy. Required wait is a function of the initial viral load. A minimum wait of 5-7 days at 22 °C is prudent. 6, 47 Heat. Heat denaturizes proteins, inactivating pathogens. High heat damages FFR materials.

Investigators seek a T, RH, and time that reliably inactivate target contaminant(s) without functional compromise. Intermediate RH facilitates heat inactivation of bacteria and multiple viruses including SARS-CoV-2. 53, 57, 64, 65 The effect of contaminating medium or fluid on inactivation time 57 may help explain significant variation in SARS-CoV-1 studies; for example, at 56 °C, the virus was undetectable after 20-90 minutes. 55, 56, 58, 95, 96 A 5-log reduction of SARS-CoV-2 in serum was measured after 56 °C × 60 minutes. 66 Similar reductions in culture media are reported after 56 °C × 30 minutes. and 70 °C × 5 minutes. 59 Heat decontamination of N95 fabric has been little studied. Fischer et al's 52 study used heat to inactivate SARS-CoV-2 on N95 fabric discs. Using mathematical modeling to extrapolate data, the calculated time to achieve a 3-log reduction using 70 °C dry heat was 48 minutes. A 6-log reduction was calculated to require 96 minutes. 52 Daeschler et al 65 Most studies report preserved filter function following T ≤100 °C. 36, 37, 52, 61, 62, 65, 67, 68 Aerosol filtration was retained in 6 N95 models after dry heat ≤90 °C × 1 hour but deteriorated following T ≥100 °C. 37 Using fewer models, recent reports also found preserved N95 filtration following 20 heat cycles ≤100 °C with wide-ranging RH, 62, 67, 68 although high RH with T >85 °C may decrease electret function. 62 Fit is generally maintained following heat-based FFR decontamination with some exceptions and model variation. 61, 69, 85 Direct contact with metal is avoided. Viscusi et al 69 Autoclave. Autoclave steam heat (typically 121-160 °C under pressure control) is an effective, widely available sterilization method. 97 However, high heat melts polypropylene and many autoclave machines cannot operate <121 °C. In encouraging reports using standard 121 °C × 15 minutes cycles, Kumar et al 78 confirmed SARS-CoV-2 decontamination on 6 N95 models. Two studies report good filter function using 1 model each. 76, 77 A third documented good functional results for multiple FFP2 models, a European standard similar to N95. 79 Model type appears especially important with standard autoclave. Folded FFR may tolerate 3-10 cycles at 121 °C without loss of fit or 0.3 μm particle filtering but some molded styles did not. [77] [78] [79] [80] Slight loss of filtration of particles <0.3 μm was observed; however, function remained above regulatory thresholds. 79 FFR decontamination with 121 °C autoclave × 15-17 minutes appears to be a viable option for up to 3 cycles. Steris (Mentor, OH) developed a customized autoclave cycle for N95 FFR decontamination that limits heat to 65 ± 5 °C × 30 minutes at 50%-80% RH held at 533 mm Hg pressure. Quantitative filtration and fit testing met NIOSH standards after 10 cycles. 48 Steris received an FDA emergency use authorization (EUA) to use their software to decontaminate 2 molded and 1 folded FFR models, ≤10 cycles. 45

Steam. Steam (not autoclave) heat has produced mixed results. Liao et al 62 reports that N95 FFR directly exposed to steam failed filtration tests after 5-10 cycles and speculated that moisture affected electret function. Other recent reports seek to help individuals wishing to decontaminate 1-2 FFR in low-resource settings. One used steam heat for FFR sealed in plastic bags and tested filter function with aerosolized surrogate coronavirus. 98 Another found more effective decontamination of MS2 virus and methicillin-resistant Staphylococcus aureus after 5 minutes of steam in a rice cooker than with dry heat at 100 °C × 15 minutes. 99 A recent report documented preserved filtration of a single N95 sample after 10 steam cycles but satisfactory fit testing only up to 3. 68 Microwave Irradiation and MWGS. MW irradiation uses radiofrequency waves, typically 2450 MHz. An alternating electrical field excites water molecules, generating heat. Its germicidal effect may result from MW irradiation and/or heat. 73 Although studies of dry MW FFR irradiation reported melted fabric or sparking of metal nose strips, 30, 62, 85 this was a minimal issue with others that included water to absorb energy and provide MWGS. 39, 61, 64, 69, 74 Filter function was retained after 3 cycles, although concerns remained about fit. 39,61,64,69 A recent report found that 3 minutes of MWGS resulted in ≥5-log reduction of MS2 phage, a virus more resistant than SARS-CoV-2. Using readily available materials, a single N95 model was effectively decontaminated with preserved fit and filter function after 20 cycles. 75 MWGS appears to be an effective option for individuals in low-resource settings.

With all heat methods using T ≤100 °C procedures must avoid cross-contamination, air FFR during cooling to inhibit resistant pathogens, and return each FFR to its original user. Model-specific data from studies of heat, autoclave, and microwave (MW) methods are available at N95decon.org. 47 HP-Based Treatments. HP, H 2 O 2 , is an effective germicide in liquid HP (LHP), vaporized (VHP), gas plasma (HPGP), and ionized (i-HP) gas states. 100 It causes free radical oxidization of DNA, RNA, and possibly other proteins and lipids. 101, 102 Although HP vapor is toxic (OSHA permissible exposure limit is 1 ppm 103 ), www.anesthesia-analgesia.org aNeStHeSia & aNalGeSia N95 Respirator Decontamination it degrades to oxygen and water. Cellulose and latex materials are avoided as they absorb HP, decreasing concentrations.

LHP was studied in preliminary FFR decontamination studies. No visible or filter damage was found following 3 cycles (30 minutes soaking in 3%-6% HP and 16-72 hours drying). 36, 61 This relatively simple method merits further investigation as published studies of fit or required drying time are lacking.

All HP studies report effective FFR sterilization of a variety of organisms, including VHP using Geobacillus stearothermophilus spores, 40 and HPGP using multiple bacteria, viruses, and spores, 53 and recent reports testing VHP and HPGP with SARS-CoV-2. 52, 78 Regarding filter function and fit, early studies demonstrated greater durability following VHP (3 cycles) than HPGP (2 cycles). 61, 85 Testing with manikins Battelle (Columbus, OH) reported preserved filtration and fit of 1 N95 model after 20 VHP cycles. 40 Straps failed before filter function. After 10 VHP cycles, Kumar et al 78 found preserved quantitative fit and filter function, using 6 FFR models. Wigginton et al 53 demonstrated filter and fit integrity after 10 cycles using 1 FFR model. Fischer et al 52 found good filter function after 2 cycles with "acceptable" function after the third, using 1 FFR model. In contrast, filter function has failed after just 1-2 cycles of HPGP in more than 1 study. 53, 78 Another recent report of the effects on 0.3 μm particle penetration of 7 FFR decontamination methods found very little change after 10 VHP cycles but damage after the third HPGP cycle, using 3 N95 models. 71 Pressure gradient data suggest that all methods damaged filter function by weakening the electret. 71 Filter damage following plasma and ionized methods may be related to higher HP concentrations. Cramer et al 83 reported on a low concentration i-HP technique (TOMI, Beverly Hills, CA) that is compatible with cellulose-containing PPE. The study found effective sterilization of Geobacillus stearothermophilus spores and retention of quantitative fit and filter function after 5 cycles, using 5 FFR models.

Proprietary HP-based sterilization equipment is prevalent in health care facilities. 46 Systems deliver 6%-60% HP in VHP, HPGP, or i-HP forms. HPGPand i-HP-based methods are quicker than VHP. Airing times range from a few minutes to 6 hours. A table of multiple proprietary systems is available on the N95decon.org website. 47 FDA EUAs have been granted to 7 companies and 2 universities to use proprietary HP-based systems for FFR decontamination during the pandemic. Some use standard equipment. Others are mobile, large-scale systems operated by the companies 45 (Table 3) .

Multiple institutions reported on their HP-based programs to decontaminate and reuse FFR during the COVID-19 pandemic. 81, 82, 84 News reports highlight calls for independent confirmation of reused FFR safety and fit as internal studies used manikins rather than FFR worn by humans. [104] [105] [106] Ultraviolet Germicidal Irradiation. Light in the UV-C range causes molecular damage when absorbed by DNA and RNA. Adequate doses prevent biologic replication. 107 Called ultraviolet germicidal irradiation (UVGI), UV-C is commonly used to decontaminate water, air, and surfaces. The delivered dose, a function of energy, area, and time, is measured in Joules/ area (J/cm 2 ). Low-pressure mercury vapor bulbs are commonly used to deliver UVGI because they emit UV light at 254 nm, very close to the maximally absorbed wavelength for nucleic acids. Other sources of UVGI include LEDs and pulsed Xenon lamps. 53, 108 Of note, tanning beds, nail salon UV light sources, and sunlight do not deliver UV-C.

UVGI decontamination of N95 FFR has been studied for a decade. 39, 41, 64, 86, 87, 95 Concerns include widely varied FFR styles, and the potential for attenuation, shadowing, and strap damage. A pathogen must be in the direct path of UV light to be inactivated; therefore, multiple light sources or separate cycles for each side are required. Straps do not rest flat and require a secondary antiseptic wipe. 39, 41, 87 Viruses are generally more sensitive to UVGI than bacteria or molds; however, SARS-CoV-1 is among the most resistant viruses to UV-C. 54 , 58 Heimbuch and Harnish 41 reported on an extensive FDA-funded study of UVGI decontamination of FFR using flu and RNA viruses, including SARS-CoV-1 and MERS coronavirus. The recommended dose was 1 J/cm 2 , 41 hundreds of times higher than required for hard surfaces. 82 FFR model differences cause significant variation in UVGI efficacy 41, 64, 87, 88 and the dose reaching each layer. 89 Adjusting calculations to account for the shape of whole FFR, Syphers 89 again found 1 J/cm 2 adequate. Mills et al 87 used artificial fluids to assess interference by skin oil or saliva. UVGI remained effective in decontaminating 12 of 15 FFR models and 7/15 straps. Fischer et al 52 applied UVGI to a single side of SARS-CoV-2-contaminated N95 fabric. The dose requirement for a 3-log reduction was 2 J/ cm 2 . Two preprint reviews recommend 2-4 J/cm 2 to each side. 54, 90 . Added time either before 54 or after 70 UVGI provides additional safety. Delivered dose must be verified with calibrated UV-C-specific sensors. Resistant pathogens may persist; therefore, protocols must prevent cross-contamination and return each FFR to its original user.

Filtration preservation is likely a function of lifetime dose. Bergman et al 61 documented preserved filtration of 6 N95 models after nearly 5 J/cm 2 . There is little independent research on filter function or fit after a cumulative dose >5 J/cm 2 or 3 "cycles." 61, 69 68 Another reports all 6 samples of 3 models failed filter and human fit tests after 10 UVGI cycles, without reported dose. 72 Strikingly, 3M reports specific models maintained NIOSH quantitative filter and fit standards after a cumulative UV-C dose of 100 J/cm 2 , their recommended maximum. 48 Chen et al 71 used an assessment of particle penetration and reported decreased filtration following the third UVGI cycle of 1 J/cm 2 using 3 mask models. Two are listed by 3M to withstand 100 J/cm 2 . 48 UVGI facilities are widely available 46 and decontamination of N95 respirators has been instituted in multiple US medical centers during the COVID-19 pandemic. Some have published detailed reports of their protocols, involving dozens of steps. [91] [92] [93] Ozone. Ozone (O 3 ) gas is an established effective germicide due to its oxidizing properties. In an initial report, ozone was used to inactivate Pseudomonas aeruginosa on multiple N95 models with no significant change in filtration for up to 10 cycles. 109 Further study is required to establish its promise for FFR.

NIOSH and the CDC moved from Normal to Contingency to Crisis Management during the winter of 2020. In early April 2020, the CDC confirmed that 90% of N95 FFR stored in the Strategic National Stockpile 110 (SNS), 11.7 million, had been released to states. 111 This represented 13% of estimated need for 6 weeks and only 1% of estimated need for a yearlong pandemic. 35, 111 Some had been stored >10 years. Results of FFR fit, filtration, and resistance testing of samples from each of 10 SNS sites showed 98% of nearly 4000 tested met NIOSH standards. 112 CDC recommendations to conserve FFR supplies include minimizing the number of people requiring respiratory protection, using alternate class respirators when feasible, extended use (longer wearing time and/or use with multiple patients), prioritizing use for those at highest risk, and limited reuse. 24 Current guidelines authorize health care use of FFR that are not normally used in health care settings, past recommended date for use, and models regulated by other countries. 24 In current CDC guidance, limited decontamination and reuse of FFR is advised for NIOSH-approved respirators only. FFR manufactured in China are specifically excluded from decontamination under EUAs. 24, 45 Any FFR that was wet, oily, soiled, stained, damaged, deformed, or no longer forms an effective seal to the face must be discarded. 6 The CDC states that the manufacturer should be consulted about any decontamination method and specifically recommends against use of a decontaminated respirator during aerosol-generating medical procedures, "given the uncertainties about the impact of decontamination on respirator performance." 6 Specific methods are not currently discussed by CDC. 6 Although 3M, a major N95 manufacturer, was not historically supportive of any decontamination or reuse of their products, 43 verification of postdecontamination filtration and fit following multiple decontamination methods is currently provided. 48, 113 3M currently recommends against conventional autoclave, MW, or any method with T >75 °C for their products. 48 US-based manufacturing is encouraged with expedited and prioritized permits 114 along with substantial government contracts. 115 Significant 3M and Honeywell production increases are underway. [116] [117] [118] FUTURE To the degree that regulatory standards specify a required degree of protection, governments are likely to drive innovation of new products designed for HCW. International FFR standards would reduce regulatory barriers that contribute to supply-chain bottlenecks when demand surges. 42,119 More testing using particles <0.3 μm was called the "greatest need for further research" by Shaffer and Rengasamy. 38 Efforts to better protect industrial workers from engineered nanoparticles 120,121 could potentially overlap to protect HCW from nanobiohazards, including viral aerosols.

High demand and potential shortages of respiratory protection devices are expected for months to years, [122] [123] [124] and novel airborne pathogens will emerge. The need for available, effective solutions has prompted an international plethora of prototypes including reusable injection molded 125 or 3-dimensional (3D) printable masks for filter inserts, 126,127 a self-disinfecting respirator, 128 nanopore membrane to cover FFR, 129 and 3D-printed frames to improve respirator fit or overcome broken straps. 130, 131 The National Institute of Health hosts a website to share 3D printable PPE innovations 131 and a recent study documents easy, effective sterilization of 3D printable materials testing many organisms including SARS-CoV-2. 132

Respiratory protection for HCW is of critical importance during the COVID-19 pandemic, 133 yet N95 FFR supply remains constrained. Conservation strategies including extended use should be used before decontamination and reuse as the risks are lower due to fewer donnings. 4, 6 For individuals with adequate stock, waiting 5-7 days between uses is advised before undertaking any decontamination. 6, 48 Manufacturers should be consulted as FFR demonstrate wide model-specific variation in durability following decontamination. 6 Large-scale methods require special equipment, substantial resources, and careful organization. Best available evidence supports moist heat, low T autoclave, MWGS, and HP-based decontamination as effective methods for SARS-CoV-2 without causing significant damage to FFR for 2-5 cycles. Minimum effective UVGI dose is 2-4 mJ/cm 2 . Filter function is a factor of cumulative dose and is generally preserved to 5 J/cm 2 . HP-based methods are effective sterilants while the other methods may not inactivate all pathogens and require procedures to prevent cross-contamination and return each respirator to its original user. Calibrated verification of each cycle of each method is required whenever possible. Questions remain. Few peer-reviewed studies comprehensively verified decontamination, filter function, airflow resistance, and fit. Laboratory conditions may not fully test realworld variables and decontamination of SARS-CoV-2 has rarely been measured on N95 materials. Fit is a critical vulnerability. Failures are frequently reported after more than 3-5 donnings, regardless of method. Users must carefully check the seal with each donning. A recent report documents increased failures following extended use and reuse by HCWs. 134 N95 decontamination and reuse remain a crisis strategy. Respirator prototypes designed for reuse are emerging. Knowledge gaps are likely to remain for the near-term; therefore, readers are encouraged to check frequently for updated guidance and new publications. We stand at the intersection of need and innovation. E 

Critical supply shortagesthe need for ventilators and personal protective equipment during the Covid-19 pandemic

A novel coronavirus from patients with pneumonia in China

Coronavirus Cases: Worldometer. Available at

Considerations for recommending extended use and limited reuse of filtering facepiece respirators in health care settings

Implementing Filtering Facepiece Respirator (FFR) Reuse, Including Reuse after Decontamination, When There Are Known Shortages of N95 Respirators

Waste not, want not: re-usability of N95 masks

Guideline for isolation precautions: preventing transmission of infectious agents in health care settings

Preparing for an Influenza Pandemic: Personal Protective Equipment for Healthcare Workers

N95 respirators vs medical masks for preventing influenza among health care personnel: a randomized clinical trial

Cochrane review: interventions for the interruption or reduction of the spread of respiratory viruses. Evid Based Child Health

Effectiveness of N95 respirators versus surgical masks in protecting health care workers from acute respiratory infection: a systematic review and meta-analysis

Surgical mask vs N95 respirator for preventing influenza among health care workers: a randomized trial

Medical masks vs N95 respirators for preventing COVID-19 in healthcare workers: a systematic review and meta-analysis of randomized trials. Influenza Other Respir Viruses

Advisors of Expert SARS group of Hospital Authority. Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS)

Factors associated with transmission of severe acute respiratory syndrome among health-care workers in Singapore

SARS among critical care nurses

BC Interdisciplinary Respiratory Protection Study Group. Protecting health care workers from SARS and other respiratory pathogens: a review of the infection control literature

Effectiveness of masks and respirators against respiratory infections in healthcare workers: a systematic review and meta-analysis

Reducing transmission of SARS-CoV-2

Airborne transmission of severe acute respiratory syndrome coronavirus-2 to healthcare workers: a narrative review

Transmission of COVID-19 virus by droplets and aerosols: a critical review on the unresolved dichotomy

Persistence of severe acute respiratory syndrome coronavirus 2 in aerosol suspensions

Strategies for Optimizing the Supply of Facemasks: COVID-19

Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis

Association between universal masking in a health care system and SARS-CoV-2 positivity among health care workers

Sourcing personal protective equipment during the COVID-19 pandemic

In pursuit of PPE

Benioff's $25 Million Blitz to Buy Protective Gear From China. 2020. The New York Times

Bans Faulty Masks, 3 Weeks After Failed Tests. 2020. The New York Times

Man Charged in Scheme to Sell 125 Million Nonexistent Masks. 2020. The New York Times

3M files lawsuit alleging N95 price in New York City. 2020. 3M Company -3M News Center. Available at

3M has sued 5 vendors who targeted emergency officials in 3 states offering billions of nonexistent N95 respirators. 2020. Available at

Macedonian Ex-Minister and a $45 Million Mask Scheme. 2020. The New York Times. Available at

Reusability of Facemasks During an Influenza Pandemic: Facing the Flu. IOM, The National Academies Press

Effect of decontamination on the filtration efficiency of two filtering facepiece respirator models

Evaluation of five decontamination methods for filtering facepiece respirators

Respiratory protection against airborne nanoparticles: a review

A pandemic influenza preparedness study: use of energetic methods to decontaminate filtering facepiece respirators contaminated with H1N1 aerosols and droplets

Research to Mitigate a Shortage of Respiratory Protection Devices During Public Health Emergencies

Frequently asked questions on PPE use and equipment

Commissioner of the U.S. Food and Drug Administration

N95 Masks: New Guidance for Addressing Shortages. ECRI. Available at

Decontamination Methods for 3M Filtering Face Respirators. Novel Coronavirus and COVID-19 Outbreak. 2020. 3M in the United States

Decreasing order of resistance of microorganisms to disinfection and sterilization and the level of disinfection or sterilization

Interim Guidelines for Biosafety and COVID-19. 2020

A scalable method of applying heat and humidity for decontamination of N95 respirators during the COVID-19 crisis

Effectiveness of N95 respirator decontamination and reuse against SARS-CoV-2 virus

Validation of N95 filtering facepiece respirator decontamination methods available at a large university hospital

Rapid evidence summary on SARS-CoV-2 survivorship and disinfection, and a reusable PPE protocol using a double-hit process

Stability and inactivation of SARS coronavirus

Evaluation of inactivation methods for severe acute respiratory syndrome coronavirus in noncellular blood products

Humidity and deposition solution play a critical role in virus inactivation by heat treatment on N95 respirators

SARS Research Team. Stability of SARS coronavirus in human specimens and environment and its sensitivity to heating and UV irradiation

Stability of SARS-CoV-2 in different environmental conditions

Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1

Evaluation of multiple (3-cycle) decontamination processing for filtering facepiece respirators

Can N95 respirators be reused after disinfection? How many times?

Factors affecting stability and infectivity of SARS-CoV-2

Effectiveness of three decontamination treatments against influenza virus applied to filtering facepiece respirators

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

A pneumonia outbreak associated with a new coronavirus of probable bat origin

Dry heat as a decontamination method for N95 respirator reuse

COVID-19 Pandemic-Decontamination of Respirators and Masks for the General Public, Health Care Workers, and Hospital Environments. 2020. Anesthesia Patient Safety Foundation

Impact of three biological decontamination methods on filtering facepiece respirator fit, odor, comfort, and donning ease

Relative survival of Bacillus subtilis spores loaded on filtering facepiece respirators after five decontamination methods

Transmission of aerosols through pristine and reprocessed N95 respirators

Is the fit of N95 facial masks affected by disinfection? A study of heat and UV disinfection methods using the OSHA protocol fit test. medRxiv

Evaluation of microwave steam bags for the decontamination of filtering facepiece respirators

Microwave-generated steam decontamination of N95 respirators utilizing universally accessible materials

Filter quality of electret masks in filtering 14.6-594 nm aerosol particles: effects of five decontamination methods

Sterilization of disposable face masks by means of standardized dry and steam sterilization processes; an alternative in the fight against mask shortages due to COVID-19

N95 mask decontamination using standard hospital sterilization technologies

Reprocessing filtering facepiece respirators in primary care using medical autoclave: prospective, bench-to-bedside, single-centre study

Multicycle autoclave decontamination of N95 filtering facepiece respirators

Decontamination and reuse of N95 respirators with hydrogen peroxide vapor to address worldwide personal protective equipment shortages during the SARSCoV-2 (COVID-19) pandemic

Institution of a novel process for N95 respirator disinfection with vaporized hydrogen peroxide in the setting of the COVID-19 pandemic at a large academic medical center

Analysis of SteraMist™ ionized hydrogen peroxide technology in the sterilization of N95 respirators and other PPE

Disinfection of N95 respirators by ionized hydrogen peroxide during pandemic coronavirus disease 2019 (COVID-19) due to SARS-CoV-2

Impact of three cycles of decontamination treatments on filtering facepiece respirator fit

Effects of ultraviolet germicidal irradiation (UVGI) on N95 respirator filtration performance and structural integrity

Ultraviolet germicidal irradiation of influenza-contaminated N95 filtering facepiece respirators

A method to determine the available UV-C dose for the decontamination of filtering facepiece respirators

Determining Exposure Times for UV-C Irradiation of PPE Filtration Facemasks for Sterilization and Potential Reuse in Times of Shortages

Decontaminating N95 masks with ultraviolet germicidal irradiation (UVGI) does not impair mask efficacy and safety: a systematic review. 2020. aNeStHeSia & aNalGeSia N95 Respirator Decontamination 91

N95 Filtering Facepiece Respirator Ultraviolet Germicidal Irradiation (UVGI) Process for Decontamination and Reuse

N95 Mask Decontamination Process. N95 Mask Decontamination Process | For Health Professionals. VCU Health

Humidity-dependent decay of viruses, but not bacteria, in aerosols and droplets follows disinfection kinetics

Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV

Inactivation of coronaviruses by heat

Guideline for disinfection and sterilization in healthcare facilities

Decontamination of face masks with steam for mask reuse in fighting the pandemic COVID-19: experimental supports

It's not the heat, it's the humidity: effectiveness of a rice cooker-steamer for decontamination of cloth and surgical face masks and N95 respirators

Chemical Disinfectants

Antiseptics and disinfectants: activity, action, and resistance

Use of hydrogen peroxide as a biocide: new consideration of its mechanisms of biocidal action

Pocket Guide to Chemical Hazards -Hydrogen peroxide

Trump administration paying huge premium for mask-cleaning machines. Which don't do the job

Mask sterilizer's safety questioned -The Boston Globe

Nurses Renew Calls To Stop Cleaning

Absorption spectra of deoxyribose, ribosephosphate, ATP and DNA by direct transmission measurements in the vacuum-UV (150-190 nm) and far-UV (190-260 nm) regions using synchrotron radiation as a light source

New Testing Confirms Xenex LightStrike Pulsed Xenon UV Robots Do Not Damage N95 Respirators. 2020. Xenex. Available at

Disinfection of N95 respirators with ozone

About the Strategic National Stockpile. phe.gov. Available at

New Document Shows Inadequate Distribution of Personal Protective Equipment and Critical Medical Supplies to States. 2020. House Committee on Oversight and Reform

NIOSH Tests the Effectiveness of PPE in National Stockpile. 2020. NETEC. Available at

3M collaborates with Decontamination Companies for N95 Respirators. 2020. 3M Company -3M News Center

NIOSH Conformity Assessment Letter to Manufacturers

DOD Awards $126 Million Contract to 3M, Increasing Production of N95 Masks. 2020. U.S. Department of Defense

3M Doubled Production of N95 Face Masks to Fight Coronavirus

Honeywell Further Expands N95 Face Mask Production By Adding Manufacturing Capabilities In Phoenix

n95-face-mask-production-by-addingmanufacturing-capabilities-in-phoenix

3M CEO on COVID-19 response: We have a unique and critical responsibility. 3M Company -3M News Center. Available at

Respirator Classification in Handbook of Respiratory Protection -Routledge Handbooks

Approaches to Safe Nanotechnology: Managing the health and safety concerns associated with engineered nanomaterials

Performance of mechanical filters and respirators for capturing nanoparticles-limitations and future direction

How the pandemic might play out in 2021 and beyond

Infection prevention precautions for routine anesthesia care during the SARS-CoV-2 pandemic

Shortage Could Last Years Without Strategic Plan, Experts Warn. HealthLeaders Media

Injection molded autoclavable, scalable, conformable (iMASC) system for aerosol-based protection: a prospective single-arm feasibility study

Rapid prototyping of reusable 3D-printed N95 equivalent respirators at the George Washington University

A Self-Disinfecting Face Mask for PPE Against COVID-19 from Technion Israel: Technion -Israel Institute of Technology

Flexible nanoporous template for the design and development of reusable anti-COVID-19 hydrophobic face masks

3D Printed frames to enable reuse and improve the fit of N95 and KN95 respirators

COVID-19 Response

Inactivation of SARS-CoV-2 and diverse RNA and DNA viruses on 3D printed surgical mask materials

Rapid Expert Consultation on the Possibility of Bioaerosol Spread of SARS-CoV-2 for the COVID-19

Pandemic. 2020. Login | The National Academies Press

Correlation between N95 extended use and reuse and fit failure in an emergency department


