Microwave- and heat-based decontamination of N95 filtering facepiece respirators: a systematic review

Since January 2020 Elsevier has created a COVID-19 resource center with spare data in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource center is hosted on Elsevier Connect, the company ‘s public news and information web site. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource center – including this research contented – immediately available in PubMed Central and other publicly fund repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with recognition of the original source. These permissions are granted for exempt by Elsevier for a hanker as the COVID-19 resource center remains active. Microwave irradiation and heat may be safe and effective viral decontamination options for N95 FFR recycle during critical shortages. The evidence does not support autoclaving or high-heat ( > 90°C ) approaches. physical degradation may be an publish for certain mask models, and more real-world evidence on burst is needed. thirteen studies were included that used dry/moist microwave radiotherapy, hotness, or autoclaving. All discussion types reduced pathogen load by a log 10 reduction gene of at least three when applied for sufficient duration ( > 30 second microwave, > 60 min dry heat ), with most studies assessing viral pathogens. Mask affair ( aerosol penetration < 5 % and airflow resistance < 25 mmH 2 O ) was preserved after all treatments except autoclaving. Fit was maintained for most N95 models, though all discussion types caused discernible physical damage to at least one model. To help inform FFR-reuse policies and procedures, our team conducted three taxonomic reviews to synthesize existing published data regarding the effectiveness of ultraviolet bactericidal irradiation ( UVGI ), inflame, microwave irradiation, and chemical disinfectants for N95 FFR decontamination [ 17, 32 ]. This review will focus on microwave- and heat-based decontamination with the following objectives : ( 1 ) to assess the effects of microwave radiotherapy and hotness on FFR performance, with specific focus on aerosol penetration and airflow resistance ; ( 2 ) to determine how effectively microwave irradiation and hotness reduce viral or bacterial load on FFRs ; and ( 3 ) to describe changes in FFR fit or physical traits caused by microwave irradiation or heat.

It is widely understand that single-use of FFRs is not sustainable in a pandemic such as COVID-19 [ [ 6 ], [ 7 ], [ 8 ] ]. FFR decontamination has been proposed as a safe method acting than standard ‘ limited recycle ’ [ 9 ], which involves no disinfection between wears [ 10, 11 ]. however, any decontamination method acting must preserve the structural and running characteristics of the disguise ( namely fit, aerosol penetration, and airflow immunity ) or it may increase risk to healthcare workers [ 12 ]. The miss of clear consensus on how to achieve condom decontamination of single-use FFRs has discouraged manufacturers and public health experts from endorsing decontamination protocols [ 13 ], although several analyses of FFR-decontamination methods have been published and the CDC has provided suggestions for decontamination in critical situations [ 14 ]. previous make has evaluated methods including radiation ( ultraviolet-C, microwaves ), damp heat ( autoclaves ), and chemical disinfectants ( bleach, ethyl alcohol, hydrogen peroxide ) [ [ 15 ], [ 16 ], [ 17 ], [ 18 ] ], which vary in their proportional efficacies and feasibilities. For case, not all institutions have access to large UV lamps, and chemical disinfection may cause significant damage to FFRs or leave hazardous residues [ 19, 20 ]. Microwaves and heat are known to inactivate viruses and bacteria [ [ 21 ], [ 22 ], [ 23 ], [ 24 ], [ 25 ] ], including coronaviruses [ 26, 27 ], and can be accessible and low-cost [ 28 ] ; however, heat and humidity may impact the electrostatic charges that confer the eminent filtration efficiency of the polypropylene filter in N95 FFRs [ [ 29 ], [ 30 ], [ 31 ] ]. During the SARS-CoV-2 pandemic, protecting frontline healthcare workers is of the last importance. As SARS-CoV-2 can be transmitted through airborne particles, the US Centers for Disease Control and Prevention ( CDC ) and the Public Health Agency of Canada ( PHAC ) have recommended the habit of N95 filtering facepiece respirators ( FFRs ) when performing aerosol-generating procedures on distrust COVID-19 patients [ [ 1 ], [ 2 ], [ 3 ] ]. N95 FFRs trickle out a minimum of 95 % of airborne particles and are the personal protective equipment ( PPE ) preferred by healthcare workers during unplayful outbreaks of aerosol-borne viruses [ 4, 5 ]. risk of bias was assessed for each result in all include studies using criteria that were predetermined by the authors relating to study design, methodological consistency, population heterogeneity, sampling bias, consequence evaluation, and selective report ( Supplementary Material ). Given the absence of an accept standard risk of diagonal assessment cock for lab studies, we created a joyride with domains applicable to FFR decontamination studies, adapted from the Cochrane risk-of-bias creature for randomized trials [ 46 ]. Mask performance was evaluated based on share aerosol penetration through the masquerade, equivalent to 100 % minus the masquerade ‘s filtration efficiency, and initial airflow underground, which is the coerce drop across the disguise. testify of success for mask performance outcomes was defined as less than 5 % aerosol penetration ( i.e. at least 95 % filtration efficiency ) and airflow resistance under 25 mmH 2 O in accord with NIOSH certification standards [ 4, 43 ]. Pathogen log 10 reduction agent of at least three, which is sufficient to in full decontaminate the highest levels of viral contaminant that are predicted to occur in hospital settings [ 44 ], was considered a successful bactericidal effect. Success thresholds for match and physical traits were a match component ( FF ) of at least 100 as per Occupational Safety and Health Administration ( OSHA ) testing guidelines [ 45 ], and no discernible changes to the dissemble, respectively. Germicidal data was reported as log 10 pathogen reduction agent calculated from absolute pathogen loads, or relative survival if the log 10 decrease divisor was not reported directly in the article. For values below minimum detectable limits, we adopted the strategy described by Heimbuch et aluminum. for imputation of log 10 reduction component : “ Based on a US Environmental Protection Agency guideline [ 41 ], half of the limit of signal detection was used to calculate log reductions for regale samples that had no detectable virus ” [ 15 ]. For Fisher et al. ’ second 2011 analyze [ 42 ], the dispute in viral load was used without a detection limit correction [ 41 ] as there was inadequate data to perform an allowance. For studies that reported a final pathogen warhead of zero and no limit of detection, log 10 reduction factor was calculated as the log 10 of the control pathogen load ( i.e. it was assumed that all virus was inactivated ). Where criterion deviation or standard error were not reported and could not be calculated across the means, generic imputation was used. If no arms within a study had a respect for uncertainty, the average value between studies was imputed for missing data. For studies that performed the lapp decontamination treatment on unlike study arms ( for example, variable mask types, durations of exposure, estrus temperatures, transmittance modes ), within-study data were averaged. All statistical analyses were performed using the R statistical program language [ 39 ]. Where two or more studies measured the lapp result using the same intervention type, cross-study data was meta-analysed using a random effects model with the R box ‘ meta ’ [ 40 ]. Variability between point estimates of studies was calculated by taking the standard deviation ( aerosol penetration and airflow resistance ) or standard error ( bactericidal effects ) across the means. Heterogeneity was assessed using an I 2 statistic ; if I 2 ≥75 %, the pool estimate was not reported. Titles and abstracts were upload to InsightScope ( www.insightscope.ca ) for title/abstract and full-text screen. At both levels of screen, citations were assessed independently in duplicate by a team of six reviewers from CHEO ( a pediatric academician hospital in Ottawa, Canada ), the University of Ottawa, and McMaster University. To ensure that all reviewers understood the eligibility criteria, the discipline leads ( S.G., A.A. ) constructed a test set of 30 citations in which five met all study criteria ( true positives ) and 25 did not ( truthful negatives ). Before gaining access to title/abstract screen, each reviewer was required to complete the screen fit and achieve a sensitivity of at least 80 %. At both title/abstract and full-text shield, records were removed entirely if both reviewers agreed to exclude ; any conflicts were reviewed and resolved by one of the cogitation leads. subsequently, the study leads reviewed the eligible citations to eliminate duplicates and confirm eligibility. The survey leads developed an origin creature for demographic and methodology data using REDCap tools hosted at CHEO and piloted the cock on five eligible studies [ 36, 37 ]. Based on the data collected on REDCap, the study leads created and piloted spreadsheets ( Microsoft Excel ) to collect data on post-decontamination aerosol penetration, airflow resistance, bactericidal effects, equip, and physical traits. In both phases of data extraction, eligible studies were divided equally among the reviewers for double, autonomous extraction, followed by conflict resoluteness by the discipline leads. Data from figures were extracted by one commentator using SourceForge Plot Digitizer ( hypertext transfer protocol : //plotdigitizer.sourceforge.net/ ) and cross-verified by a second base commentator. Extracted data and meta-data of all records screened are available on OSF [ 38 ]. Two journals were besides hand-searched, as they were particularly relevant to the review but are not indexed in any of the aforesaid databases : Journal of the International Society for Respiratory Protection and Journal of Engineered Fibers and Fabrics. Two authors ( M. S. Bergman and D. J. Viscusi ) had been previously identified as publishing frequently on disguise decontamination ; Scopus was searched 29 th March 2020 for those authors and N95-related terms. A search of Google Scholar ( 29 th March 2020 ) yielded 1630 hits. The first 1000 were downloaded to Publish or Perish and screened until 50 consecutive irrelevant records were found. Records up to that point were saved as an RIS charge and edited to remove patents, reports and books. The WHO database on COVID-19 ( 29 th March 2020 edition ) was searched. Disaster Lit : database for Disaster Medicine and Public Health, MedRxiv and OSF Registries were searched 29 th March 2020 for the condition “ N95 ” and records pertaining to decontamination were selected and downloaded. All references were entered into an Endnote file where duplicate records were removed. Following screen, one librarian ( M.S. ) reviewed the reference lists of admit studies to identify any potentially relevant studies not included in the screen set. Two health sciences librarians ( L.S. and M.S. ) searched the following databases for relevant literature : medline and Medline in Process via OVID, Embase Classic + Embase via OVID, and Global Health via CAB Direct. A research strategy was developed in Medline, and then translated into the other databases as appropriate ( Supplementary Material ). All databases were searched from 1 st January 1972 to 29 th March 2020 for English and french publications. eligible studies met the follow criteria : ( 1 ) survey was an master article or taxonomic follow-up ; ( 2 ) study investigate decontamination of N95 ( including surgical N95 ) filtering facepiece respirators or their components ; ( 3 ) survey included a decontamination arm involving microwave irradiation or inflame treatment ; ( 4 ) at least one of the follow post-treatment outcomes was reported : ( i ) FFR performance ( aerosol penetration, airflow resistance ) ; ( two ) decrease in viral/bacterial burden ; ( three ) disguise fit ; ( intravenous feeding ) changes in physical traits. Articles besides had to be available in English or french and published after 1972, the first year that an FFR was approved by the National Institute for Occupational Safety and Health ( NIOSH ) [ 35 ]. We excluded abstract-only publications, discipline protocols, guidelines, commissioned reports, editorials, narrative reviews, book chapters, and patents. A full risk of bias assessment for all report outcomes is presented in the Supplementary Material. overall risks of bias across all studies for aerosol penetration and airflow resistance outcomes were humble. risk of bias for bactericidal outcomes was moderate for most studies, chiefly ascribable to gamble of population heterogeneity ( i.e. masks not from same lot ) and the use of unblinded ocular assays. risk of bias for fit was tone down in all studies, due either to high hazard of sampling bias or centrist hazard for both population heterogeneity and methodology. Risks of bias for physical traits varied between studies, but unblinded/subjective result evaluation and electric potential population heterogeneity were common reasons for increased risk. Changes in smell were assessed in three studies [ 18, 50, 52 ] ; the alone meaning increase in smell was noted in the 3M 1860 after MHI in one sketch [ 52 ]. impossible urine retentiveness, defined as over 1 g of water retained after drying for 1 henry, was observed in three ( 3M 1860, 3M 8210, Cardinal Health ) of six models tested [ 42 ]. physical changes were both treatment- and model-dependent. The 3M 1870 expose coherent separation of the inner foam nose cushion after MGS and MHI, with this change not observed in any early masquerade exemplary [ 15, [ 50 ], [ 51 ], [ 52 ] ]. Melting of some models occurred after MGS, dry microwave, or dry heat at temperatures of 100°C or greater [ 18, [ 49 ], [ 50 ], [ 51 ] ]. Autoclaving led to significant mask distortion in two of three studies [ 19, 49 ]. Four studies assessed FFR match after microwave and/or heat treatment ( ) [ 46, 47, 51, 52 ]. Viscusi et aluminum. abbreviated the standard OSHA paroxysm test [ 45 ] from eight exercises to six [ 52 ]. An FF, scored from 1 ( poor equip ) to 200 ( best fit ), was calculated by measuring the proportion of ambient atom concentration outside the respirator to the particle concentration inside. Each subject donned each mask five times, with two replicates per model-treatment combination, and a multi-donning suit agent ( MDFF 10 ) was calculated as the harmonic mean of the 10 FFs. MDFF 10 exceeded the pass threshold of 100 for all models after MGS and MHI treatments. Bergman et alabama. used an abbreviate OSHA match test exchangeable to Viscusi et al., but performed three cycles of decontamination with a single-donning match test before the first treatment and after each of the three cycles [ 51 ]. The match screen evanesce rate after three MGS or MHI cycles was 95 % for all models. Fischer et aluminum. incorporated 2-h wear periods between each of three dry heating system rounds and performed fit-testing using the official four-exercise modified OSHA protocol initially and after each decontamination-wear cycle ; deterioration of fit was lone seen in two ( of six ) replicates after the third discussion [ 47 ]. Kumar et alabama. fit-tested four N95 models after one, three, five, and ten autoclave cycles using normal and trench breathing exercises alone [ 48 ]. Across all four studies, most replicates of all tested models maintained adequate burst for all interventions tested, with the exception of the 3M 1860 after multiple ( > 1 ) cycles of Kumar et al. ’ randomness autoclave treatment. In the four studies that examined the bactericidal effect of MGS [ 15, 42, 53, 54 ], all arms demonstrated a log 10 viral reduction factor greater than three except the two rapid-treatment arms ( 30 sulfur or less ) in Fisher et al. ’ s 2009 study [ 54 ]. All studies using inflame treatment against viral pathogens ( dry, MHI, and autoclave ) besides reported log 10 decrease factors in excess of three [ 15, 47, 48, 53 ], although this alone occurred after 60 min at 70°C dry heat in Fischer et al. ’ randomness SARS-CoV-2 study and not at 10-, 20-, or 30-min timepoints [ 47 ]. Bacterial decontamination using rapid ( 3-min ) high-temperature dry inflame in Lin et al. ’ sulfur study resulted in a log 10 reduction divisor of only 2.5, although this was increased to three after a 24-h incubation at ‘ worst case ’ temperature/humidity ( 37°C, 95 % proportional humidity ) [ 16 ]. In the like study, no colonies grew post-autoclave treatment. Three studies examined airflow resistance simultaneously with aerosol penetration (, ) [ 18, 19, 50 ] ; of these, there were two microwave decontamination arms ( one damp and one dry ) and three heat arms ( one MHI, one dry, and one autoclave ). initial resistance to airflow was reported in millimetres of water column altitude pressure. Where testing was performed, minimal to no increase in airflow resistance was noted, and all final values were within NIOSH guidelines ( < 25 mmH 2 O ) [ 43 ].

Five studies assessed aerosol penetration after heat treatment (, ) [ 18, 19, 49, 50, 53 ], four of which had at least one damp circumstance ( MHI or autoclave ). MHI was applied for 20–30 min [ 50, 53 ] and, for all mask models, the increase in aerosol penetration was small ( < 1 % ) and remained within NIOSH documentation standards ( < 5 % penetration ) [ 4 ]. Results in autoclave conditions varied : in one study no increase was noted after 15-min treatment [ 19 ], while another noted increases of over 18 % and 34 % for 15- and 30-min treatments, respectively [ 49 ]. Three studies examined aerosol penetration post-dry heat treatment and reported small increases with all final examination values remaining within NIOSH authentication standards except the Kimberly–Clark PFR95-270 after 60 min at 110°C ( 5.4 % penetration ) [ 18, 19, 49 ]. about all studies that measured aerosol penetration [ 18, 42, 49, 50, 53 ] utilized a neutralize solid polydisperse sodium chloride aerosol ( count median diameter ( CMD ) = 75 ± 20 nanometer, geometric standard deviation ( GSD ) ≤1.86 ) and a flow rate of 85 L/min over full masks as per NIOSH documentation testing procedures [ 4 ]. The exception was Lin et al., who used a lower flow rate ( 5.95 L/min ) to generate equivalent airfoil speed on smaller dissemble segments, and measured penetration of a range of particle sizes using a neutralize potassium sodium tartrate tetrahydrate aerosol ( CMD = 101 ± 10 nanometer, GSD = 2.01 ± 0.08 ) [ 19 ]. Microwave and heat treatments were performed in dry conditions or with the addition of moisture. Two studies used dry microwave treatment [ 18, 49 ], and seven included a reservoir of water or steam bulge within the microwave chamber, creating microwave-generated steam ( MGS ) [ 15, 42, [ 50 ], [ 51 ], [ 52 ], [ 53 ], [ 54 ] ]. Five studies used dry heat ( oven or rice cooker ) [ 16, 18, 19, 47, 49 ], five employed damp heat incubation ( MHI ) by adding water reservoirs inside ovens or using testing ground incubators [ 15, [ 50 ], [ 51 ], [ 52 ], [ 53 ] ], and four used an autoclave [ 16, 19, 48, 49 ]. thirteen studies were included in this review ( ). The studies were published between 2007 and 2020, and all were performed in the USA except one from Canada and two from Taiwan. The two studies that investigated the novel coronavirus were published as pre-prints and not yet peer-reviewed at the time of inclusion body [ 47, 48 ]. Microwave and heat-based interventions were investigated in nine and 11 studies, respectively. sixteen unlike mask models were used across the studies, with the 3M 1860 ( N = 8 ), 3M 1870 ( N = 7 ), 3M 8210 ( N = 7 ), and 3M 8000 ( N = 5 ) being the most normally tested. The initial database and journal searches identified 466 and three records, respectively, and two extra studies were identified via consultation with leaders in the field ( ). After twin removal, 418 unique records remained for screening. All six reviewers achieved a sensitivity of 100 % on the test plant before beginning screening. The review team excluded 397 records at the title/abstract tied ( κ = 0.79 ). Three records were excluded after full-text review, resulting in 18 reports representing 13 singular studies eligible for inclusion ( κ = 0.77 ). No extra studies were found from checking reference lists of include manuscripts .


In answer to PPE shortages during the COVID-19 pandemic, we systematically reviewed the existing literature on N95 FFR decontamination using microwave irradiation and heating system. Our results indicate that moist/dry microwave radiotherapy and moist/dry heat between 60 and 90°C can efficaciously deactivate viral pathogens on certain N95 FFR models while maintaining mask match and function within acceptable ranges. General manipulation of high heat ( greater than 90°C ) and autoclaving are not supported by the testify in recapitulation as these interventions compromised the integrity of multiple disguise models. decontamination of N95 masks for recycle is worthwhile only if the masks retain their ability to remove at least 95 % of viral particles from the air out ( i.e. aerosol penetration < 5 % ) [ 4 ]. In the six studies that evaluated aerosol penetration after microwave and/or heat treatment, only two studies showed an increase in penetration above the standard 5 % doorway [ 18, 49 ]. The decontamination conditions in these studies ( temperature above 100°C and autoclaving ) were besides associated with meaning physical degradation of the mask. interestingly, despite observing physical degradation, Lin et aluminum. reported no significant change to aerosol penetration after autoclaving [ 19 ]. This discrepancy may be explained by the non-standard protocol used by Lin et al., which involved mask fragments, modified flow rate, and a different aerosol solution, precluding direct comparison with NIOSH aerosol penetration guidelines. Mask serviceability does not entirely depend on filtration efficiency. N95 FFRs cause breathing resistance and reduce air commute volume at baseline [ 55 ] ; frankincense, if microwave- or heat-treatment were to increase airflow resistance significantly, this could render the masks intolerable, specially when break for extend periods during PPE rationing [ 10 ]. Three studies in this review evaluated airflow resistance in a sum of five different decontamination conditions ( MGS, dry microwave, MHI, dry heating system, and autoclave ) [ 18, 19, 50 ]. The concluding average airflow resistance never reached even 50 % of the maximum allowable resistance indicated in NIOSH-established guidelines for any mask exemplar [ 43 ], and most models demonstrated slender reductions in resistance after decontamination, making airflow resistance an improbable obstacle to N95 decontamination using microwave beam or heat. Microwave irradiation and estrus both effectively reduced viral load on FFRs, with all interventions displaying a log10 viral reduction component greater than three when applied for sufficient duration. Although studies used masks that were artificially contaminated in the lab quite than those that had been contaminated during clinical use, viral load titres that are sufficient for observation of a three log10 decrease factor meet or exceed the highest levels of viral contamination modelled to occur in hospital settings [ 44 ]. Germicidal affect can be far bolstered by leaving the masks for several days after decontamination before recycle : there is evidence that SARS-CoV-2 naturally decays over fourth dimension on surfaces [ 56 ], and Lin et aluminum. demonstrated that bacterial load was far reduced 24 h after incubation, even in warm, humid conditions [ 16 ]. For SARS-CoV-2, a wait time of at least three days is advisable as viable virus is detectable up to 72 h after application on some surfaces [ 56 ]. N95 FFRs must fit with a compressed varnish to ensure that air passes immediately through the filter. Data regarding post-decontamination masquerade fit was promising, but most study protocols did not account for the impacts of repeated donning–wearing–doffing cycles. previous research indicates that fit failure is associated with extended consumption and limited recycle of masks even without any decontamination treatment [ 57, 58 ]. thus, applying microwave/heat discussion to idle masks, as three of the four studies did, has limited generalizability. The exception was the protocol used by Fischer et al., which included 2-h wear cycles between each discussion and demonstrated that fit deteriorated after the third decontamination-donning cycle [ 47 ]. Kumar et al. ’ south positive post-autoclave meet results, which did not include wear-periods between cycles, must be interpreted with extra circumspection as they only tested fit using breathing exercises, which are not congressman of functional movements of healthcare workers [ 48 ]. Overall, the results of these studies indicate that a limited number of microwave or heat decontamination cycles may not compromise paroxysm ; however, further testing is required using masks that have undergone prolonged wear clock time and multiple donning–doffing cycles. Regardless, a careful drug user seal bridle should be performed by any healthcare actor who dons a decontaminate FFR, just angstrom would be done when donning a newly one [ 59 ]. forcible abasement of an N95 FFR will about constantly causal agent changes in fit, function, and tolerability. Melting of masquerade components was observed in some microwave and heating system arms and depended on the mask exemplary, temperature, and discussion duration. frequent adverse physical changes were observed at temperatures over 90°C, which corresponds to the maximum manoeuver temperature of polypropylene, the polymer that comprises the N95 filter [ 60 ]. gamey temperature was besides the likely lawsuit of melting during microwave treatments : a previous sketch demonstrated that wet kitchen sponges can exceed 90°C after 1 minute of microwave irradiation [ 25 ]. separation of the inner foam nose cushion was a coherent issue for the 3M 1870 after microwave and heat treatments, but did not lead to a significant reduction in fit and so may not preclude recycle if the mask feels tolerable to the user [ 52 ]. Autoclaving does not appear to be a desirable decontamination option for rigid FFRs as it caused significant physical deformations to the 3M 8000 and 3M 1820 [ 19, 49 ]. Although Kumar et aluminum. did not notice any significant physical changes after their autoclave intervention, functional degradation did occur in the one fixed mask model ( 3M 1860 ) while the three flexible ‘ pleated ’ mask models maintained their structural and functional integrity [ 48 ]. therefore, it is potential that autoclaving may be effective for pleat N95 varieties, although this needs far study. Fisher et alabama. 's 2011 study contained the sole examination of water memory post-MGS discussion [ 42 ]. notably, their results corresponded with hydrophobicity evaluations performed by Viscusi et aluminum. [ 18 ] for the five disguise models that were shared between the two studies : entirely the masks with all hydrophobic trickle layers ( i.e. urine droplets applied by Viscusi et alabama. beaded on each layer 's surface and were not absorbed ) showed acceptably low water memory levels in Fisher et al. ’ mho study. As residual moisture may occlude mask pores and increase breathing resistance, hydrophobicity should be a consideration when choosing which mask models to sterilize using damp microwave or heating system methods if dry time is limited [ 61, 62 ] .

Future directions

While the results of this review provide a begin degree for the development of institutional microwave- or heat-based FFR decontamination protocols, there are several key gaps in the existing evidence. For exemplar, few studies investigated fit ; without a close seal, air will flow through the gaps between the dissemble and the wearer ‘s face, bypassing the trickle wholly and making outcomes of aerosol penetration and airflow resistor irrelevant. The characteristics of the micro-organisms used in respective of the bactericidal studies must besides be taken into bill when extrapolating these results to the SARS-CoV-2 coronavirus. Influenza A viruses, such as H1N1 and H5N1, are enveloped, approximately 120 nm in diameter, and covered in glycoproteins [ 63 ] ; coronaviruses share all of these characteristics and may credibly respond in a alike manner to inflame and radiation [ 64 ]. notably, effective decontamination was reached by Heimbuch et alabama. for H1N1 at a lower temperature and shorter timepoint than in Fischer et al. ’ sulfur experiment using SARS-CoV-2 [ 15, 47 ]. It is ill-defined whether the presence of moisture in Heimbuch et al. ’ south treatment may have increased bactericidal efficacy, or if SARS-CoV-2 is more insubordinate to heat than influenza. MS2, as investigated by Fisher et aluminum. in two studies [ 42, 54 ], is less comparable as it consists of a non-enveloped 26-nm virion [ 65 ], and the bacterial species ( Bacillus subtilis ) in Lin et al. ’ randomness evaluation is further distinct [ 16 ]. The use of different viruses besides necessitates the use of unlike assays ( for example, brass or TCID50 ) and cell types according to the infectious properties of each virus, and these different tests may not have comparable sensitivities. however, reproducible potent bactericidal effects across interventions and pathogens support the notion that these methods should reduce the load of SARS-CoV-2 to undetectable levels if applied for sufficient clock. additionally, it should be noted that no studies using moderate-temperature MHI interventions quantified growth of non-target bacteria, which could increase under damp heating system conditions and pose a separate infectious risk .

Risk of bias

The moderate hazard of bias seen in most studies for bactericidal outcomes arises from the fact that all studies quantified pathogens using brass, colony, or TCID50 assays ; while these are wide accepted means of quantifying viral and bacterial load, they involve ocular procedures that are not fully objective, and no studies stated that the lab technicians were blinded to discussion and control designations. Two studies that evaluated equip replaced and re-tested masks when their straps broke or melted [ 51, 52 ] ; it is possible that this discounted data from the samples that were most vulnerable to physical damage, which could positively skew the fit scores. similarly, there were two models ( 3M 1870, 3M 8000 ) for which aerosol penetration and/or airflow electric resistance could not be measured after certain treatments due to melting [ 18, 49 ] ; these were appropriately accounted for within the articles ‘ conclusions and therefore did not significantly increase within-study hazard of bias, but the absence of measurements from these more-vulnerable masks could positively bias the results of the systematic review. For physical trait outcomes, several studies reported observations in the results without indicating physical evaluation in their objectives or methods, and/or merely commented on changes in some mask models without indicating that unmentioned models were unaffected, making it unmanageable to rule out methodological inconsistencies and selective report.

Strengths and limitations

This is a rigorous taxonomic review, involving a peer-reviewed search strategy, an a priori registered protocol, train and test of the screening/extraction team, and attachment to PRISMA reporting guidelines [ 34 ]. however, the heterogeneity of the microwave and heat parameters across the 13 studies limits the ability to draw overarching conclusions about any one plant of conditions. temperature, pressure, and moisture all influenced outcomes, specially in heat-decontamination arms where an autoclave provides a vastly different environment than a dry heat rice cooker. There was evidence that different mask models have unlike physical vulnerabilities, indicating that the reception of a given mask model to a particular treatment does not predict how any other exemplary will react. Germicidal outcomes showed consistent viral reduction, but the artificial contaminant of samples limits extrapolation to the clinical fructify. The results of this revue should therefore be used as a resource for determining which microwave and heat conditions may be most auspicious but can not guarantee the success of any specific protocol. In termination, in situations where sufficient new PPE is available, recycle of N95 FFRs should not be considered. however, in a position where procurement of new masks is not possible, this systematic review indicates that microwaves and heat may both be suitable options for FFR decontamination. Microwave beam and moderate-temperature heat ( up to 90°C ), in both damp and dry conditions, demonstrated effective decontamination of viral pathogens without compromising mask performance or affair. The most significant limitations to the application of available testify are the differential effects on specific dissemble models, particularly regarding physical deterioration, and the miss of real-world data regarding changes in fit. Autoclaving is an effective disinfectant, but caused significant abasement and decrease of filter efficiency in some mask types, and so its use is not supported by the results of this review. overall, any hospital implementing these decontamination methods would benefit from monitoring the physical responses of their mask models to determine which, if any, are durable in these treatment conditions, and for how many treatment cycles. niobium : The Association of Home Appliance Manufacturers has emphasized the importance of not using home appliances to microwave or heat facemasks due to risk of damage or wound [ 66 ] .