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. 2020 Jun 25;11(3):e00997-20.
doi: 10.1128/mBio.00997-20.

Microwave-Generated Steam Decontamination of N95 Respirators Utilizing Universally Accessible Materials

Katelyn E Zulauf #  1   2 , Alex B Green #  1 , Alex N Nguyen Ba  3 , Tanush Jagdish  4   5 , Dvir Reif  6 , Robert Seeley  7 , Alana Dale  7 , James E Kirby  8   2
Affiliations

Microwave-Generated Steam Decontamination of N95 Respirators Utilizing Universally Accessible Materials

Katelyn E Zulauf et al. mBio. .

Abstract

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has caused a severe, international shortage of N95 respirators, which are essential to protect health care providers from infection. Given the contemporary limitations of the supply chain, it is imperative to identify effective means of decontaminating, reusing, and thereby conserving N95 respirator stockpiles. To be effective, decontamination must result in sterilization of the N95 respirator without impairment of respirator filtration or user fit. Although numerous methods of N95 decontamination exist, none are universally accessible. In this work, we describe a microwave-generated steam decontamination protocol for N95 respirators for use in health care systems of all sizes, geographies, and means. Using widely available glass containers, mesh from commercial produce bags, a rubber band, and a 1,100-W commercially available microwave, we constructed an effective, standardized, and reproducible means of decontaminating N95 respirators. Employing this methodology against MS2 phage, a highly conservative surrogate for SARS-CoV-2 contamination, we report an average 6-log10 plaque-forming unit (PFU) (99.9999%) and a minimum 5-log10 PFU (99.999%) reduction after a single 3-min microwave treatment. Notably, quantified respirator fit and function were preserved, even after 20 sequential cycles of microwave steam decontamination. This method provides a valuable means of effective decontamination and reuse of N95 respirators by frontline providers facing urgent need.IMPORTANCE Due to the rapid spread of coronavirus disease 2019 (COVID-19), there is an increasing shortage of protective gear necessary to keep health care providers safe from infection. As of 9 April 2020, the CDC reported 9,282 cumulative cases of COVID-19 among U.S. health care workers (CDC COVID-19 Response Team, MMWR Morb Mortal Wkly Rep 69:477-481, 2020, https://doi.org/10.15585/mmwr.mm6915e6). N95 respirators are recommended by the CDC as the ideal method of protection from COVID-19. Although N95 respirators are traditionally single use, the shortages have necessitated the need for reuse. Effective methods of N95 decontamination that do not affect the fit or filtration ability of N95 respirators are essential. Numerous methods of N95 decontamination exist; however, none are universally accessible. In this study, we describe an effective, standardized, and reproducible means of decontaminating N95 respirators using widely available materials. The N95 decontamination method described in this work will provide a valuable resource for hospitals, health care centers, and outpatient practices that are experiencing increasing shortages of N95 respirators due to the COVID-19 pandemic.

Keywords: COVID-19; MS2 phage; N95; SARS-CoV-2; disinfection; respirator; reuse; sterilization.

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Figures

FIG 1
FIG 1
N95 respirator microwave steam decontamination by ceramic mug either inside or in the absence of Ziploc containment. (A) Image of ceramic mug decontamination system. A 10-cm-diameter mug was filled with 60 ml of distilled water and covered with mesh from a produce bag, secured with a rubber band. Triplicate N95 1-cm2 coupons were placed on top of the mesh. The mug was then placed in the microwave either in a sealed, ventilated Ziploc bag or directly into the microwave. (B) After a 1-min microwave treatment, with or without Ziploc bag enclosure, or a 60-min treatment with dry 105°C heat, phage was extracted from N95 coupons and quantified by plaque assay. Triplicate untreated N95 coupons were included as controls in all assays. There was no significant reduction in plaque titer between Ziploc bag-enclosed and open-mug decontamination systems or between dry-heat-treated and untreated controls (P = 0.9 or P = 0.66, respectively, as determined by analysis of variance (ANOVA) with Holm Sidak posthoc test). PFU, plaque-forming units, a direct measure of viable viral titer; n.s., not significant.
FIG 2
FIG 2
N95 respirator decontamination by microwave-generated steam over an open ceramic mug. (A) Triplicate N95 coupons treated with 107 PFU MS2 were placed on the mesh-covered ceramic mug and treated for the indicated durations in an 1,100-W microwave. After treatment, phage was extracted from N95 coupons and quantified by plaque assay. (B) We next evaluated treatment of an entire N95 respirator on the mug decontamination system. (C) 107 PFU of MS2 was spotted on 10 premarked sections of a whole N95 respirator as indicated. (D) After a 3-min treatment in an 1,100-W microwave, demarcated pretreated segments measuring 1 cm2 were excised from the respirator, and MS2 phage was then extracted and quantified by plaque assay. Triplicate untreated precut N95 coupons were included as a control in all assays. Bars shown are means and standard deviations of phage titers from each excised segment from a single respirator. An asterisk indicates that no viable MS2 were detected. The limit of detection of all assays is 10 PFU. Data shown are representative of three separate respirator experiments.
FIG 3
FIG 3
N95 respirator decontamination with microwave-generated steam over an open glass container. (A and B) Image of glass container decontamination system. A 17 cm × 17 cm glass container was filled with 60 ml of distilled water, covered with mesh from a produce bag, secured with a rubber band. (C) Triplicate N95 respirator coupons inoculated with 107 PFU MS2 phage, placed on the mesh-covered container, and treated for indicated times in an 1,100-W microwave. After treatment, MS2 phage was extracted from N95 coupons and quantified by plaque assay. (D) 107 PFU of MS2 phage was spotted onto 10 different premarked locations on a N95 respirator as indicated. (E) The whole N95 respirator was then treated for 3 min as shown in panel B in an 1,100-W microwave. Demarcated segments measuring 1 cm2 encompassing the area of inoculation were excised from the respirator, and MS2 phage was extracted and quantified by plaque assay. Triplicate untreated precut N95 coupons were included as a control in all assays. Data shown are the means and standard deviations of plaque titers from a single respirator and are representative of three separate experiments. In one experiment, no viable PFU were detected from all excised segments (data not shown). An asterisk indicates that no viable MS2 was detected. The limit of detection of all assays is 10 PFU.
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