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

Objective There are widespread shortages of personal protective equipment as a result of the COVID-19 pandemic. Reprocessing filtering facepiece particle (FFP)-type respirators may provide an alternative solution in keeping healthcare professionals safe. Design Prospective, bench-to-bedside. Setting A primary care-based study using FFP-2 respirators without exhalation valve (3M Aura 1862+ (20 samples), Maco Pharma ZZM002 (14 samples)), FFP-2 respirators with valve (3M Aura 9322+ (six samples) and San Huei 2920V (16 samples)) and valved FFP type 3 respirators (Safe Worker 1016 (10 samples)). Interventions All masks were reprocessed using a medical autoclave (17 min at 121°C with 34 min total cycle time) and subsequently tested up to three times whether these respirators retained their integrity (seal check and pressure drop) and ability to filter small particles (0.3–5.0 µm) in the laboratory using a particle penetration test. Results We tested 33 respirators and 66 samples for filter capacity. All FFP-2 respirators retained their shape, whereas half of the decontaminated FFP-3 respirators showed deformities and failed the seal check. The filtering capacity of the 3M Aura 1862 was best retained after one, two and three decontamination cycles (0.3 µm: 99.3%±0.3% (new) vs 97.0±1.3, 94.2±1.3% or 94.4±1.6; p<0.001). Of the other FFP-2 respirators, the San Huei 2920 V had 95.5%±0.7% at baseline vs 92.3%±1.7% vs 90.0±0.7 after one-time and two-time decontaminations, respectively (p<0.001). The tested FFP-3 respirator (Safe Worker 1016) had a filter capacity of 96.5%±0.7% at baseline and 60.3%±5.7% after one-time decontamination (p<0.001). Breathing and pressure resistance tests indicated no relevant pressure changes between respirators that were used once, twice or thrice. Conclusion This small single-centre study shows that selected FFP-2 respirators may be reprocessed for use in primary care, as the tested masks retain their shape, ability to retain particles and breathing comfort after decontamination using a medical autoclave.

Please comment on dry vs moist heat. Autoclave devices are variable in setting/temperature/time -the results on your device may not translate. Dry/Moist heat has been done for COVID-19 and 70C for 30 minutes did not inactivate Fisher Morris et al 2020. This may partially support your higher temp/time/humidity. However, a single H1N1 test is not an appropriate surrogateplease comment.
By the time this is published, the few cases of anecdotal uses of cloth masks will be dated.
It has been recommended that health care workers do not use masks with exhalation valves. Please comment.
The 3M 1860 series of respirators has some of the highest structural integrity. The challenge during the shortage is that the "best" respirators are not available and many of the others would potentially fail fit testing. Please comment on the importance of fittesting ANY respirator. Ozog et al JAAD 2020.
Any visible contamination including saliva/mucous/external fluid will affect results. Subjects should only reuse their own respirators in this setting. The process is to label respirators as has been done is hydrogen peroxide FDA EUA.
Decontaminated respirators should not be used for aerosolizing procedures, regardless of decontamination method. Please add.
Thank you for this work which can potentially benefit small offices that currently have autoclave devices, understand fit testing, and have access to high quality respirators. The limited capacity (4 respirators over 34 minutes) precludes widespread use.

REVIEWER
Wen-Yinn Lin National Taipei University of Technology  Taiwan  REVIEW RETURNED 03-Jun-2020

GENERAL COMMENTS
1. Particle generation system and number concentration of different sizes are suggested to be provided. 2. What could be the reason why the filter capacities of one-and two-time sterilized San Huei 2920V for 5.0 micrometer-sized particles were lower than that for 1.0 micrometer. 3. The filter capacities of new Safe Worker 1016 (1.0 micrometer) and one-time sterilized (0.3 micrometer) were significantly lower than other particle sizes. Moreover, the capacity for 0.3 micrometer decreased from 96.5 to 60.3 after one-time sterilization, while it (for 1.0 micrometer) increased from 60.5 to 90.1. What could be the reason? 4. Did deformity result in significant change of flow resistance?

VERSION 1 -AUTHOR RESPONSE
Reviewer: 1 Comment 1. The introduction or discussions could compare or cite more references on decontamination of N95FFRs, especially Raymond J. Roberge, Ronald E. Shaffer and Chane-Yu Lai. Response 1. Dr Roberge is mentioned in the discussion on the physiological impact of valve-type and non-valved N96 filtering facepiece respirators. Dr. Shaffer is mentioned in reference 9 regarding the user seal check. We put information on this procedure in the discussion part of the manuscript. Dr. Chane-Yu Lai is also included in the manuscript, namely cited in the important paper on (PloS ONE 2017;12:e0186217).
Comment 2. In methods, the fit test is more useful than user seal check.
Response 2. While this is correct; the user seal check is test that can be easily performed in the clinic without the need of scarcely available and expensive FIT test equipment and should therefore also be included.
Comment 3. Also, in particle penetration test, "the 28 liter of surrounding air is sucked through the filter material of the mask and the remaining particles are counted in the categories of 0.3, 0.5, 1.0 and 5.0microns". The 28 liter was not enough or match the requirement for the EN-149 sampling flow rate or face velocity. Moreover, the tested particle size barely included the most penetrating particle size (MPPS) of electret N95FFRs. Response 3. As these suggestions are very valid, we now stated in the limitations: "Also, we presumed that solid particles of 0. Comment 4. Masks that can reuse, not only including fit and decreased risk of spreading other diseases, but also the filter quality or acceptable filtration efficiency, and bioefficacy. Suggest add some references or redo some experiments. Response 4. We have rewritten relevant sections in the discussion paragraphs. Please see the paragraphs "prior studies on heat as a decontamination method" and "prior studies on the reuse of respirators".
Comment 5. Strongly recommend the authors to calculate the filter quality of each tests before and after decontamination, and describe the discrepancies between the decontamination. Response 5. We have calculated the filter quality of each sample, of unused respirators, as well as single, and multiple decontamination cycles. Please see table 1.
Comment 6. The whole article did not compare the bioefficacy of any bacteria or viruses after decontamination. Did the decontamination process work well or not? What are the decontamination criteria? How do the authors make sure that the decontamination method is good or not? Response 6. Our group previously demonstrated that steam decontaminated respirators proved negative for bacteria [11]. Others have performed further study on bioefficacy. We have added the following paragraph to the discussion section of the manuscript. (please see italic text below). Moreover in our "implications for practice" paragraph we have also provided practical tips, such as: 1) do not use reprocessed respirators in the event of aerosol-generating procedures (per CDC recommendations); 2) mark reprocessed respirators with the wearer's initials as well as the number of reprocessing cycles.
"From the literature there is a consensus that thermal inactivation is a very efficient technique to eliminate viruses. [2,6,7,11,13]  Response 4. We have added information on this topic in the paragraph "implications for practice", which can be found in the discussion section of the manuscript.
Comment 5. The 3M 1860 series of respirators has some of the highest structural integrity. The challenge during the shortage is that the "best" respirators are not available and many of the others would potentially fail fit testing. Please comment on the importance of fit-testing ANY respirator. Ozog et al JAAD 2020.
Response 5. We agree that the 3M 1860 series provide high structural integrity. While we agree that fit and material testing is of at most importance as one cannot determine the quality of a respirator in any other way, it is our belief that this is somewhat out of the scope of this manuscript and the message we bring to the audience.
Comment 6. Any visible contamination including saliva/mucous/external fluid will affect results. Subjects should only reuse their own respirators in this setting. The process is to label respirators as has been done is hydrogen peroxide FDA EUA. Response 6. We agree that this will affect the results.
Comment 7. Decontaminated respirators should not be used for aerosolizing procedures, regardless of decontamination method. Please add. Response 7. We agree that this is the case, however in primary care settings these types of procedures are extremely rare.

Reviewer: 3
Comment 1. Particle generation system and number concentration of different sizes are suggested to be provided.