Summary of guidance

We reviewed 3 guidance documents from the US CDC ^6,13,14 and 1 each from the ECDC, ¹⁵ the PHE, ¹⁶ and the WHO. ⁷ All were published or updated between March 17, 2020, and May 21, 2020, and were written for the COVID-19 pandemic. None included a systematic literature search, and the depth of referencing and level of detail varied. All guidance documents depicted extended use, reuse, or reprocessing of single-use masks and respirators as extraordinary, last-resort measures to be considered only during a critical shortage of equipment when other strategies for rational use of supplies have been exhausted (eg, minimizing need for PPE through administrative and engineering controls and coordinating supply-chain management). The US CDC, the WHO, and PHE recommend additional procedures at the organizational level: appropriate documentation and recording of reuse or reprocessing, quality assurance of reprocessing measures, suitable reprocessing and storage facilities and systems, and staff training regarding safe use and donning or doffing of masks or respirators if reusing or extending use.

All guidance documents favored extended use over reuse because of reduced risk of contact transmission. All recommended ensuring good fit, performing a seal check, and inspecting for function and potential damage prior to use or reuse of any mask or respirator. The US CDC and the WHO acknowledged that face masks and respirators that have passed their expiry date may sometimes be used in situations of limited capacity. Table 1 summarizes guidance on the extended use and reuse of surgical masks; findings are grouped by the 3 forms of risk mitigation shown in Figure 1. Table 2 summarizes guidance on extended use and reuse of respirators. Table 2 also summarizes guidance on reprocessing of respirators, which were framed with caution to reflect the high degree of uncertainty and potential risk.

Table 1. Summary of Guidance Recommendations for Fluid-Resistant Surgical Masks

Note. CDC, Centers for Disease Control and Prevention; ECDC, European Centers for Disease Control and Prevention; PHE, Public Health England; WHO, World Health Organization.

^a PHE guidelines on extended use and reuse do not clearly differentiate between surgical masks and filtering face-piece respirators.

^b “Fold” cannot apply to molded-cup–type face masks.

Table 2. Summary of Guidance Recommendations for Filtering Face-Piece Respirators

Note. CDC, US Centers for Disease Control and Prevention; ECDC, European Centre for Disease Prevention and Control; PHE, Public Health England; WHO, World Health Organization.

^a PHE guidelines on extended use and reuse do not clearly differentiate between surgical masks and filtering face-piece respirators

^b “… can be re-used for a limited time, unless there is a risk for contamination through the deposition of infectious particles on the surface.”

^c States that filter capacity of FFP3/FFP2/N95 respirators greatly exceeds one day of use in healthcare or social care.

^d Reused and reprocessed respirators are likely to be used for extended periods, in this case the extended use criteria also apply.

^e Currently appears in decontamination guidelines as an alternative to decontamination but does not appear in the reuse guideline.

^f Unless manufacturer information indicates that decontamination does not affect performance.

Systematic reviews

The 3 systematic reviews were conducted between March and April 2020 and at the time of submission were preprints or were under peer review. All were conducted in Canada; 3 were conducted by the same research team. These 3 focused on reprocessing of filtering face-piece respirators using different decontamination interventions (ie, heat-based treatments, disinfectant, and ultraviolet germicidal irradiation), ^{Reference Gertsman, Agarwal and O’Hearn17–Reference O’Hearn, Gertsman and Webster19} and 1 study covered reprocessing of surgical masks and ‘precontamination’ interventions applied before use to enable extended use or reuse. No reviews in our sample examined the impact of extended use or reuse of filtering face-piece respirators or surgical masks on the ability to meet technical standards or on healthcare worker acceptability outcomes such as comfort. The AMSTAR 2 ratings for each study are provided in Supplementary File 4 (online). The included reviews were judged to be predominantly of high quality. However, none provided a list of excluded studies or justified the reasons for exclusion, and no study reported on the sources of funding for included primary studies.

Detailed descriptions of the reviews and their findings are provided in Supplementary File 5 (online). The 3 reviews on filtering face-piece respirators included between 11 and 13 studies (28 unique studies in total). The included studies evaluated the effects of reprocessing on various outcomes including effective decontamination, appearance, performance (including filtration efficiency and airflow resistance), user comfort, fit, and safety (ie, increased contagion risk to healthcare workers due to insufficient decontamination and/or toxicity due to residual decontaminant). In relation to decontamination, most of the evidence in the reviews supported vaporized hydrogen peroxide, moist/dry heat (range, 60–90°C), and ultraviolet germicidal irradiation interventions. The studies included in the reviews were generally at low risk of bias. However, few primary studies investigated the impact of these methods on fit or user comfort, and there was substantial variability in the models of filtering face-piece respirator used across studies. Only 2 studies ^{Reference Fischer, Morris and van Doremalen20,Reference Kumar, Kasloff and Leung21} included in 1 review ^{Reference O’Hearn, Gertsman and Webster19} explored the effect of reprocessing on SARS-CoV-2. In addition, 7 studies were included in the review of surgical mask decontamination, but only 1 of these had specifically evaluated decontamination interventions after use to enable reuse. The review concluded that there was insufficient evidence regarding the safety or efficacy of any decontamination intervention for reprocessing surgical masks.

Comparison of guidance and systematic reviews on reprocessing of masks or respirators

Table 3 compares the findings of the systematic reviews with the 3 guidance documents relating to the reprocessing of surgical masks and respirators. There is considerable discrepancy to the extent that no single reprocessing method is supported by all the guidance documents. The intervention with most support is vaporized hydrogen peroxide, though one document cautions about chemical residues and another indicates that it has only been tested with some of the respirator models in common use. Similarly, ultraviolet germicidal irradiation receives both cautious support and concerns about inadequate decontamination because of incomplete penetration into deeper layers of the filter. Moist heat is cited as promising, though there are concerns when steam is microwave generated because it may be uneven heating and the metal nose-band may generate sparks.

Table 3. Summary of Systematic Review Conclusions Compared to Guidance Recommendations for Reprocessing Methods^a

Note. CDC, US Centers for Disease Control and Prevention; ECDC, European Centre for Disease Prevention and Control; PHE, Public Health England; WHO, World Health Organization; UV, ultraviolet.

^a No data are given for PHE because no recommendations have been made in their guidance.

^b The CDC identified these methods as showing most promise and recommends focusing current efforts on these technologies.

Inconsistencies and gaps in evidence

Our review of guidance documents and systematic reviews highlights several inconsistencies that warrant exploration, even though the COVID-19 pandemic presents unique challenges for different contexts. This is particularly true of the emerging science of reprocessing respirators, for which authorities appear to have proceeded with different degrees of caution in making recommendations.

Although the ECDC recommends the addition of either a surgical mask or a cleanable face shield over a respirator, the US CDC strongly recommends a face shield rather than a surgical mask due to supply issues and concerns that a surgical mask could affect the function of the N95 respirator. Moreover, evidence suggests that the addition of a surgical mask does not improve respiratory protection and may increase user discomfort and impair communication. ^{Reference Radonovich, Cheng, Shenal, Hodgson and Bender22,Reference Radonovich, Yanke, Cheng and Bender23}

The US CDC and ECDC make specific recommendations regarding respirators and aerosol-generating procedures. Both recommend discarding and not reprocessing respirators after use in aerosol-generating procedures, and the US CDC also recommends not using a reprocessed respirator while carrying out an aerosol-generating procedure (subject to manufacturer guidance). However, the WHO and PHE do not explicitly recommend that respirators be discarded after aerosol-generating procedures, nor do they mention the use of reprocessed respirators in aerosol-generating procedures. No guidance mentions the use or discarding of respirators in areas where aerosols may be present.

Guidance regarding the reuse of respirators without reprocessing is inconsistent and lacks clarity. The WHO guidance strongly discourages the reuse of respirators without appropriate decontamination. However, citing a recent study by Van Doremalen et al ^{Reference van Doremalen, Bushmaker and Morris24} suggesting that SARS-CoV-2 viral particles may remain infective for up to 72 hours, the US CDC suggests a system in which each healthcare worker is allocated 5 respirators for daily use in strict rotation, using careful storage to essentially ‘quarantine’ the devices. The US CDC suggest that if 5 respirators are not available for each worker, then decontamination may be necessary, potentially suggesting that this should be an initial strategy prior to attempting reprocessing. We found no systematic review evidence testing this approach, and neither PHE or ECDC explicitly discuss reuse with or without reprocessing. Moreover, data from the study cited showed that the 72-hour period was just the length of the measurement period and that survival followed a decay curve, not a fixed “all dead” time, implying that the length of time an amount greater than or equal to the infective dose survives depends on the starting quantity of virions. ^{Reference van Doremalen, Bushmaker and Morris24}

The systematic reviews included laboratory studies to test whether reprocessing changed the properties of a respirator. None of the reviews or research reported in guidance documents described practical or operational studies of facilitating reuse or reprocessing of respirators at scale. This is a key gap in the research, given the existing strain on healthcare resources and the requirement to ensure that a respirator remains matched to a healthcare worker throughout its use.