key: cord-0877447-rmlyc4js
authors: Pascoe, M.J.; Robertson, A.; Crayford, A.; Durand, E.; Steer, J.; Castelli, A.; Wesgate, R.; Evans, S.L.; Porch, A.; Maillard, J.-Y.
title: Dry heat and microwave generated steam protocols for the rapid decontamination of respiratory personal protective equipment in response to COVID-19-related shortages
date: 2020-07-09
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2020.07.008
sha: 4c972b0340486900e3bd7357e6067987e2fb64f8
doc_id: 877447
cord_uid: rmlyc4js

BACKGROUND: In the wake of SARS-CoV-2 pandemic and unprecedented global demand, clinicians are struggling to source adequate access to personal protective equipment. Respirators can be in short supply, though are necessary to protect workers from SARS-CoV-2 exposure. Rapid decontamination and reuse of respirators may provide relief for the strained procurement situation. METHOD: In this study, we investigated the suitability of 70(o)C dry heat and microwave-generated steam (MGS) for reprocessing of FFP2/N95-type respirators, and Type-II surgical face masks. S. aureus was used as surrogate as it is less susceptible than enveloped viruses to chemical and physical processes. RESULTS: We observed >4 log(10) reductions in the viability of dry S. aureus treated by dry heat for 90 minutes at 70°C and >6 log(10) reductions by MGS in 90 seconds. After 3 reprocessing cycles, neither process was found to negatively impact the bacterial or NaCl filtration efficiency of the respirators that were tested. However, MGS was incompatible with Type-II surgical masks tested, as we confirmed that bacterial filtration capacity was completely lost following reprocessing. MGS was observed to be incompatible with some respirator types due to arcing observed around some types of metal nose clips and by loss of adhesion of clips to the mask. CONCLUSION: Considering the advantages and disadvantages of each approach, we propose a reprocessing PPE/face mask workflow for use in medical areas.

Background 24

In the wake of SARS-CoV-2 pandemic and unprecedented global demand, clinicians 25 are struggling to source adequate access to personal protective equipment. 26

Respirators can be in short supply, though are necessary to protect workers from 27 SARS-CoV-2 exposure. Rapid decontamination and reuse of respirators may 28 provide relief for the strained procurement situation. 29

Method 30

In this study, we investigated the suitability of 70 o C dry heat and microwave-31 generated steam (MGS) for reprocessing of FFP2/N95-type respirators, and Type-II 32 surgical face masks. S. aureus was used as surrogate as it is less susceptible than 33 enveloped viruses to chemical and physical processes. 34

We observed >4 log 10 reductions in the viability of dry S. aureus treated by dry heat 36 for 90 minutes at 70°C and >6 log 10 reductions by MGS in 90 seconds. After 3 37 reprocessing cycles, neither process was found to negatively impact the bacterial or 38

Introduction 47

Respiratory personal protective equipment (PPE) such as respirators, and surgical 48 masks (SMs) are essential for infection control and the protection of healthcare 49 workers. Following the spread of the SARS-CoV-2 pandemic, worldwide demand 50 has raised procurement issues for healthcare providers. Frontline workers and media 51 outlets widely report that supply has become restricted in many facilities, potentially 52 jeopardising the health of workers and patients. One approach for addressing supply 53

shortages is the re-use of PPE and face masks, which are normally regarded as 54 single use items. Re-use could dramatically increase the number of masks available 55 during emergency situations, until production capabilities are able to meet demand. 56 57 There are key challenges posed by the reuse of masks which must be considered to 58 make informed decisions on whether to utilise such an approach. During use, 59 microorganisms are deposited onto masks from the environment and the wearer. 60

Although SARS-CoV-2 is the current concern, as an enveloped virus, it does not 61 necessarily present a challenge for disinfection or sterilisation processes. [ A laboratory MINI/6 incubator (Genlab Ltd) was used to provide dry heat and was set 148

to 70 o C. Temperature was monitored with a glass thermometer whilst relative 149 humidity was monitored with a digital hygrometer (Traceable; Fisher Brand). Relative 150 humidity remained below the lower limit of detection of this device (25%) throughout 151 the experiments. Samples were placed in the dry heat from 5-90 minutes. Inoculated 152 membranes were placed on a folded N95 respirator as described above, and the 153 respirator placed on a shelf in the centre of the incubator. 154 155

Following decontamination processes, inoculated membranes were aseptically 157 removed from the masks and placed individually in 50 mL centrifuge tubes 158 containing 5 g sterile glass beads and 10 mL resuspension medium (TSC 159 supplemented with 0.1% polysorbate-80). Tubes were vortexed for 1 minute to 160 dislodge cells into the resuspension medium. Suspensions were serially diluted in a 161 10-fold series using sterile TSC. Aliquots of 20 µL volume of each dilution were 162 plated in triplicate on a TSA plate. To increase the lower limit of detection, 500 µL 163 aliquots of the resuspension media (i.e. the 10 0 dilution) were also used to prepare 164 spread plates on TSA using sterile L-shaped spreaders. Following overnight 165 incubation at 37 o C, colonies were counted and log 10 reductions were calculated 166 relative to the untreated controls. The lower limit of detection using this approach 167 was calculated as 2 CFU/mL. A >4 log 10 reduction in CFU/mL was used as a target 168 value for determining whether the approaches we explored for reprocessing were 169 effective. afforded a 35mm diameter was tested. NaCl was nebulised to an average mobility 214 size of 56 nm. Size distribution was determined by differential mobility spectrometry, 215 rather than photo-optical methods of mass measurement. 216 217 Assessment of particle penetration was assessed in a similar manner as has been 218 previously reported [11] . The cut sections of pristine and reprocessed respirators or 219 masks were sequentially tested within a stainless-steel filter holder within the NaCl 220 

Two approaches were successful at achieving the target of >4 log 10 reductions in S. 277 aureus dry inoculum viability (Table I) (Table II) (Table III) . Decontamination of 303 respirators with either dry heat or microwave generated steam was not found to have 304 a negative impact on bacterial filtration efficiency, even after 3 reprocessing cycles. 305

In all cases, the number of bacteria recovered from processed surfaces was below 306 the lower limit of detection. 307 308 Impact of decontamination procedures on NaCl aerosol filtration efficiency 309 35 mm cut sections of pristine surgical masks provided 50% NaCl filtration efficiency 310 whilst pristine N95 respirators provided 98% NaCl filtration efficiency (Figure 4) . 311

There were no detectable changes (P >0.05; ANOVA, Dunnett) in performance 312 between pristine and reprocessed masks of any type, even after three reprocessing 313 cycles. Notably, N95 masks could be reprocessed with MGS in combination with 314 essential oil. might be more susceptible to these processes than other microorganisms including 353 mycobacteria [17] . If other microorganisms, such as mycobacteria, were a concern, 354 these should be tested. 355

We found that microwave-generated steam (1800W, 90 sec, 100 or 200 mL water in 357 'steriliser') and dry heat (70 o C for 90 min) were both effective in decontaminating 358 surgical masks and respirators. Whilst dry heat was not found to negatively impact 359 function of PPE or face masks, microwave-generated steam was incompatible with 360 surgical masks and some models of respirator. The Kimberly-Clark FFP2/N95-type 361 respirators used in this study were able to be reprocessed with either method and 362 could be effectively disinfected within 90 seconds. In addition, Type-II surgical face 363 masks and FFP2/N95-type respirators were able to be reprocessed up to three times 364 without negatively impacting their function. The addition of lemon-scented essential 365 oil to the microwave-generated steam process was not found to negatively impact 366 NaCl filtration efficiency, indicating that such oils may be added to a microwave 367 steam steriliser to impart a fresh fragrance onto the PPE if desired. It might not 368 however cover strong malodours. Dry heat reprocessing is less manually intensive 369 and may be more easily scaled-up to high volume reprocessing workflows. It is also important to note that other PPE brands might respond differently to dry 388 heat and microwave generated steam processes, and that different microwave 389 ovens would need to be validated; in particular, domestic microwave ovens typically 390 have much lower power (600W) and use rotating turntables rather than rotating 391 antenna, so a longer exposure time would be needed and they might not achieve the 392 same results. Here, we observed that the use of an industrial-grade 2.45 GHz 393 microwave oven at a 1800 W setting for 90 seconds with 100 mL water in the 394 steriliser was incompatible with some FFP2/N95-type respirator. respirators should be exposed to a thermal cycle of a) for 24 h to a dry atmosphere 409 of (70 ± 3°C) and b) for 24 h to a temperature of (-30 ± 3°C), before allowing to 410 return to room temperature for at least 4 h, ensuring that no thermal shock occurs, 411 prior to testing, it is supported that the 70°C dry heat method discussed in this paper 412

should not be detrimental. 

Selection and use of disinfectants In practice

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Sterilization of disposable face masks by means of standardized 456 dry and steam sterilization processes; an alternative in the fight against mask 457 shortages due to COVID-19

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