Background

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the coronavirus pandemic (COVID-19), has affected the world and changed the way we live [1,2,3,4,5]. Aerosols, droplets, secretions, and direct contact with nasal mucosa are the main respiratory transmission routes of these viruses between humans [6].

Health professionals have been using respiratory protection masks; particularly model N95, in the care of infected patients for aerosol-generating procedures (tracheal intubation, non-invasive ventilation, tracheotomy, cardiopulmonary resuscitation, manual ventilation, before intubation, collections of nasotracheal secretions, and bronchoscopies). The recommendation is to discard them after close contact with a patient (single-use) [7,8,9].

During the current COVID-19 pandemic, governments have found it difficult to acquire adequate amounts of personal protection equipment (PPE), including respiratory protection masks. This has been accompanied by a high level of infection of health professionals on the front lines of care provided for sick people [26]. Therefore, based on the recommended approaches of a rapid review [25], only the risk of bias assessment of the included studies was not carried out. Challenging scenarios such as the onset of coronavirus demand that decision makers receive the best evidence quickly and urgently, making traditional methods of systematic review unviable [27].

Criteria for considering studies for this review

Based on these recommended approaches [25], we developed a specific protocol for this study (Supplementary material 1). We planned to include only primary research studies that evaluated methods for the decontamination of N95 masks for reuse and whose outcome was the effectiveness, safety, maintenance of protection, or filtering characteristics of the evaluated decontamination method were included. Therefore, we could answer the question: “How effective and safe are decontamination methods for respiratory protection masks model N95/PFF2 against respiratory viruses?”

Information sources for identification of studies

We followed the limit main database searching recommended by Cochrane Rapid Reviews Methods Group [27]. Therefore, searches were conducted on MEDLINE, Cochrane Library, and EMBASE databases on September 25, 2020. Search terms were related to decontamination (e.g., “Sterilization,” “Disinfection,” and “Decontamination”), reuse (e.g., “Equipment Reuse” and “Reuse”), device failure (“Equipment Failure”), and masks (e.g., “N95” and “filtering facepiece respirators”).

The search strategy was developed in two stages. In the first stage, an experienced researcher (LFP) structured the strategies with the collaboration of different specialists (AIQC, ATGG, JV, MCCF, AMMP, JOB, and SMVLO). In the second stage, a researcher (AJG) who is trained by the Cochrane Systematic Reviews Group evaluated and validated the search strategies. The review did not have a date or language restrictions. The complete search strategies can be found in Table 1 of Supplementary material 2; therefore, they are valid, reliable, and reproducible.

Searching other resources

In addition to searching the official databases, the reference lists of all studies selected for full-text reading, as well as the review articles identified in official searches, were scrutinized to identify possible eligible studies.

Selection process

Two reviewers (LFP and AIQC) independently screened for the title, abstracts, and full text, the reviewers used the Rayyan systematic review application in blind mode [28]. Disagreements during the selection process were resolved by discussion with a third review (SMLVO). Mendeley citation management software was used for the automatic removal of duplicate articles.

Data collection process and analysis

Two reviewers (LFP and AIQC) independently used a pre-specified data extraction sheet form, in duplicates, designed to obtain the specific data required for this review. The data extracted from the primary studies were data related to the author, year, study objective, intervention, comparator, commercial mask model, target microorganism, results, and conclusions of the study authors, limitations, and detailed description of the decontamination process making its reproducibility in other scenarios possible. Moreover, authors of the included primary studies were also contacted to provide data that was not available in the manuscripts.

Data synthesis

The characteristics of each study (cycles, temperatures, protocols, densities, exposure time, technology used, and results) are presented in Table 3 of Supplementary material 4 [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76]. The differences before and after decontamination are shown in Table 4 of Supplementary Material 5 for outcomes: filter aerosol penetration, filter airflow resistance, and filtration efficiency. Results of the studies were summarized based on the decontamination method and results for the two following issues [53]:

  1. 1.

    Whether the device maintains its structural characteristics and provides an adequate level of protection after the decontamination method, without any risk of exposure for the health professional (as inhalable chemical residues that may have remained after the method used). The penetration of 0.3 μm (aerodynamic mass mean diameter) of sodium chloride aerosols aerosol particles through a certified N95 respirator cannot exceed 5% [77]. Also inhalation and exhalation resistance to airflow of certified N95, i.e., filter airflow resistance utilizing a filter tester at 85 l/min of constant airflow, shall not exceed 35mm (343.2 Pa) water column height pressure and upon initial exhalation shall not exceed 25mm (245.1 Pa) water column height pressure. These are specifications required for certification as a 95% filtration efficiency level [78].

  2. 2.

    Whether the decontamination method used was effective in reducing or eliminating the infectious capacity of the target organism without any risk of exposure for the health professional to contamination. This criterion can be verified when the mean log reduction of the microorganisms allows us to state that the mask has reached non-infectious levels, as recommended by the FDA, at level 1 with a reduction (≥6-log) of more resistant spores and Mycobacterium. Alternatively, using a quantitative molecular amplification assay (quantitative real-time polymerase chain reaction) that shows if there was a reduction in the levels of detectable viral RNA, with the absence of any pathogenic infectious agent [53].

Results

Search results

The complete search strategies can be found in Table 1 of Supplementary material 2. Initial searches retrieved 552 articles (MEDLINE: 381, Cochrane: 52, and EMBASE: 119). The reference lists of all studies selected for full-text reading, as well as the review articles identified in official searches, were scrutinized to identify possible eligible studies. Authors of the included primary studies were also contacted. These manual searches detected 11 additional publications that were added to the total recovered. Mendeley citation management software was used for the automatic removal of duplicate articles, leaving 301 studies remaining.

Selection process

Two reviewers (LFP and AIQC) independently screened the 301 studies using the Rayyan systematic review application to screen abstracts and titles [28]. Of these, 240 were excluded for not meeting the inclusion criteria. The full texts of 61 studies were screened by two reviewers (LFP and AIQC), and thirteen additional studies were excluded. Excluded full-text studies and the reasons for exclusion are listed in Table 2 of Supplementary material 3 [79,80,81,82,83,84,85,86,87,88,89,90,91]. At the end, 48 studies were selected for the full-review process (Fig. 1).

Fig. 1
figure 1

PRISMA flow-chart of the study selection process

Full size image

Fifteen methods were assessed in the 48 papers: hydrogen peroxide, ultraviolet irradiation, ethylene oxide, dry heat, moist heat/pasteurization, ethanol, isopropanol solution, microwaving, sodium hypochlorite (NaClO), autoclaving, electric rice cooker, cleaning wipes, bar soap, and water, multi-purpose high-level disinfection cabinet (Altapure, Mequon, WI), and chlorine dioxide (ClO2) [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,15, 94].

Limitations and strengths of this review

As reported in the results, the search strategy was developed by an experienced researcher and validated by another systematic review researcher, who is trained by the Cochrane Systematic Reviews Group. However, it was not developed by a health information specialist. Considering that this was the review that found the largest number of studies that were in fact eligible and included compared to previous reviews which investigated different mask decontamination methods (model N95) [18, 19], we do not consider this a limitation. As a rapid review, another limitation concerns a series of methodological simplifications adopted, which may affect the findings and our interpretations. Eliminating the evaluation of the studies’ methodological qualities was among the simplifications and calls for caution in interpreting the results presented. The technical aspects of outcome assessment in the included studies were not taken into account in this review and is an important limitation when interpreting the presented results.

The strengths of this review, however, are the number of identified decontamination methods and its unfolding results which points to practices that may be adopted and further studied as they seem to present better results initially, the multiple approaches used to search for relevant studies, such as contact with various authors and manual search of article references, and the participation of a team of multi-disciplinary specialists in all stages of the project, which included professionals from the areas: nursing, dentistry, medicine, pharmacy, and physical therapist.

Agreements and disagreements with other reviews

A previous systematic review that included 15 studies concluded that future studies were required in order to establish the efficacy and safety of N95 decontamination methods [18]. Other systematic reviews have reported that masks can be decontaminated with microwave irradiation and moderate-temperature heat (up to 90°C), in both moist and dry conditions [20] and a single cycle of vaporized H2O2 can be used as a chemical disinfectant to remove viral pathogens without degrading the masks [22]. Our review is broader than the cited ones, which shows that our search strategy is much more sensitive. However, there is not sufficient evidence concerning UVGI as a safe decontamination method [21] To our knowledge, this is the first rapid review to assess 15 different decontamination methods identified in 48 studies, providing an overview of all available methods.

Implications for future research studies

Whereas the current evidence is insufficient to determine a safe and widely accessible method, even for countries with financial limitations, our review points to an important gap in the evidence base, despite recent research efforts. In addition, considering the possibility of new challenging pandemic scenarios, investigating decontamination methods for reuse of protection professional equipment has an environmental, social appeal, and economic aspect. Moreover, it is important to invest in new fabric technologies that are prepared to be reused.

Conclusion

Access to effective PPE should be guaranteed for health care workers on the front lines of pandemics. However, there is currently insufficient evidence to recommend any method as being safe and effective for the decontamination and reuse of respiratory protection masks. Even though there are several promising methods worth for further studies such as hydrogen peroxide vapor, germicidal ultraviolet irradiation, dry heat at temperatures ≤85°C, wet heat/pasteurization, and the microwave oven, this rapid review has exposed all methods for decontamination need further evaluation and validation in real-life scenarios, also considering economic issues for implementation.