Findings and Recommendations
The threat of an influenza pandemic is likely to be with us for some time, as new strains will continue to emerge and travel quickly through the new global economy. In the absence of vaccines or effective treatments, nonpharmacological interventions such as hygiene, social distancing, and the use of respirators and medical masks must be implemented as secondary means of preventing or slowing transmission. Of these, many public health practitioners regard the use of respirators and masks to be an intervention of last resort.
With adequate time and planning, stockpiling or ramping up production, or both, would ensure that there would be enough respirators or medical masks for all those who may need them, but with limited resources and time, supplies are likely to be insufficient. Thus, reality may require that disposable N95 respirators and medical masks be pushed beyond their approved uses in the hope that they can offer some level of protection beyond their intended limits of use. Moreover, individuals with no access to respirators or masks, even disposables, may feel driven to invent their own respiratory protection measures; for example, they may don woven masks not approved for medical uses in the United States, or use household items such as towels or sheets.
Although the scientific community continues to debate the mechanisms of influenza transmission, most experts agree that pandemic influenza will be spread in the same way as seasonal influenza (DHHS, 2005).
what measures can be taken that would permit the reuse of disposable N95 respirators in healthcare settings?
what is known about the need for, and development of, reusable face masks for healthcare providers and the general public?
In the short time available, the committee reviewed the published literature on respirator and mask effectiveness, infectious disease control, and occupational health and industrial hygiene and spoke with representatives of industry, the public health community, government agencies, regulators, and the international community. Despite the extensive literature on respiratory protection, data are severely limited in some critical areas, leading the committee to rely on its collective judgment about what would constitute responsible and safe reuse of N95 filtering facepiece respirators or medical masks.
Existing literature and guidance indicate that there is a hierarchy of respiratory protection, with some respirators offering higher levels of safety than others. The committee was asked to focus on N95 filtering facepiece respirators and medical masks because they are affordable, widely available, and likely to be used in the event of an influenza pandemic. The committee was also asked to assess whether there are any cost-effective alternatives to N95 filtering facepiece respirators and medical masks that could provide adequate levels of protection and could be used against the influenza virus during a pandemic.
In reaching its conclusions, the committee formed some assumptions. First, of the forms of respiratory protection the committee was asked to consider, N95 filtering facepiece respirators that are certified by the National Institute for Occupational Safety and Health (NIOSH) and properly fit-tested are likely to provide the best protection against influenza to the extent that it may be spread via an airborne route. Similarly, a closely fitting high-efficiency medical mask is likely to provide appropriate protection against droplets, whereas a surgical N95 will provide protection against both droplets and aerosols. While recognizing the methodological and data limitations regarding the efficacy of medical masks as a form of respiratory protection against avian influenza, and in the absence of data to the contrary, the committee concluded that masks are likely to provide far less protection against aerosols than an N95 filtering facepiece but may offer
better protection than cotton masks, homemade alternatives such as handkerchiefs and scarves, or no protection at all. No device is fail-safe, and its effectiveness depends on fit, level of exposures, and appropriate use. Finally, none of these devices protects against contact transmission, and appropriate hand hygiene is necessary when using and after removing these devices.
In this final chapter, the committee provides findings and recommendations about reuse of N95 filtering facepiece respirators and medical masks and recommends a research agenda that could help the nation prepare for near- and long-term pandemic threats.
A properly fitted N95 filtering facepiece respirator is likely to be both the least expensive and the most widely available NIOSH-certified respirator for protecting healthcare workers and the public against airborne infection. However, without manufacturing modifications, current disposable N95 respirators cannot be effectively cleaned and should therefore be discarded after a single use. Moreover, manufacturers are concerned that should extended use or reuse after cleaning and disinfection of disposal devices be recommended, they will incur higher liability without federal policies to protect them. In addition, the need for fit-testing respirators is critical and must be an integral part of any program that promotes their use.
Finding 1: The committee could not identify or find any simple modifications to the manufacturing process that would permit disposable N95 respirators to be reused without increasing the likelihood of infection.
Finding 2: Any method of decontaminating a disposable N95 filtering facepiece respirator must remove the viral threat, be harmless to the user, and not compromise the integrity of the various elements of the respirator. The committee found no method of decontamination that met all three criteria.
Finding 3: The committee found no simple modifications to currently existing N95 filtering facepiece respirators that would obviate the need for fit-testing.
Finding 4: Many versions of reusable (elastomeric) respirators on the market have facepieces that can be cleaned and reused. Some of these are available in full-facepiece versions that also offer eye protection and may prevent conjunctival transmission. These respirators can be reused by single or multiple wearers and, although they are more expensive than the disposable N95 respirators, should be considered as an alternative to filtering facepieces.
The filter media are discarded and replaced when they become unsuitable for further use, for example, when they are damaged or dirty or when breathing resistance is unacceptable. Like N95 filtering facepieces, the filter media cannot be cleaned or decontaminated by any currently acceptable means. However, it is possible that with appropriate handling, the cartridges can be reused after multiple cleanings of the elastomeric facepiece.
Despite these findings about the constraints of reuse, the committee makes a recommendation for extending the life of disposable N95 respirators for individual users. This recommendation is consistent with the Centers for Disease Control and Prevention’s (CDC’s) Interim Domestic Guidance on the Use of Respirators to Prevent Transmission of SARS (CDC, 2003).
Recommendation 1: Avoiding Contamination Will Allow for Limited Reuse.
If an individual user needs to reuse his or her own N95 filtering facepiece respirator, the committee recommends it be done in the following manner:
Protect the respirator from external surface contamination when there is a high risk of exposure to influenza (i.e., by placing a medical mask or cleanable faceshield over the respirator so as to prevent surface contamination but not compromise the device’s fit).
Use and store the respirator in such a way that the physical integrity and efficacy of the respirator will not be compromised.
Practice appropriate hand hygiene before and after removal of the respirator and, if necessary and possible, appropriately disinfect the object used to shield it.
Use of a respirator will be compromised if it does not pass a user seal check, if breathing resistance is unacceptable, or if there are obvious defects in the respirator’s structure. The choice of a fluid-resistant cover (faceshield or medical mask) should be dictated in large part by functionality and availability.
MEDICAL MASKS AND IMPROVISED PROTECTION
In its discussions with manufacturers, the committee was told that currently marketed disposable medical masks are made of materials that are likely to degrade with standard means of disinfection (e.g., chemicals, heat, radiation). Because medical masks are intended for disposal and are submitted to the Food and Drug Administration (FDA) with that labeling, manufacturers have no reason or incentive to develop methods for decontamination or reusable masks. However, manufacturers with whom the committee spoke noted that several disposable devices currently on the market can be used repeatedly by the same wearer until they become damaged, moist, difficult to breathe through while wearing, or visibly soiled. The length of use is, in general, related to the durability of the mask, and its ability to withstand moisture. Because reuse of the same device by infected patients is unlikely to increase the risk of contamination, medical masks can be reused by patients until the masks are no longer useable due to moisture or damage.
FDA informed the committee that it has not cleared any medical mask/ N95 filtering facepice respirator or medical mask as a reusable device. The agency also indicated that if such a device became available it would perform an expedited review of the premarket submission to meet the public health need. Thus, FDA recommends that without manufacturing modifications, current medical (surgical and procedure) masks commonly used in the United States cannot be effectively cleaned and should therefore be discarded after a single use.
Finding 5: Any method of decontaminating a medical mask must remove the viral threat, be harmless to the user, and not compromise the integrity of the various elements of the mask (e.g., tear or deform the filter, stretch the elastic attachments, bend the nose clip). The committee found no validated method of decontamination that meets these criteria.
The committee also reviewed the limited data available about the effectiveness of cotton masks or alternative materials for respiratory protection. Regulatory standards for an appropriate personal protective device require that a medical mask should not permit blood or other potentially infectious fluids to pass through to or reach the wearer’s skin, mouth, or other mucous membranes under normal conditions of use and for the duration of time that the protective equipment will be used. Because it is not clear that cloth masks or improvised masks can meet these standards and without better testing and more research, cloth masks or improvised masks generally have not been recommended as effective respiratory protective devices or as devices that would prevent exposure to splashes.
Finding 6: Woven cloth masks currently available in Asia are being reused in the clinical setting after washing and decontamination. The committee recognizes that these masks may be the only option available for some individuals during a pandemic. Given the lack of sufficient data either supporting or refuting the effectiveness of woven cloth masks in blocking influenza transmission and fluid resistance, the committee hesitates to discourage their use but cautions that they are not likely to be as protective as medical masks or respirators. The committee is concerned that their use may give users a false sense of protection that will encourage risk taking and/or decrease attention to other hygiene measures.
None of the currently available cloth masks has been reviewed according to FDA’s regulatory criteria for use as a medical mask.
Finding 7: The committee recognizes that in the absence of any alternative, some members of the public may improvise respiratory protection (e.g., T-shirts, handkerchiefs, or scarves) against transmission of influenza when it is necessary to enter an infected environment, such as when caring for an infected family member at home. Given the lack of sufficient data either supporting or refuting the effectiveness of such actions, the committee hesitates to discourage their use but cautions that they are not likely to be as protective as medical masks or respirators. The committee is concerned that their use might give wearers a false sense of protection that will encourage risk taking and/or decrease attention to other hygiene measures. The tighter the structure of the fabric, the bet-
ter the potential for filtration. At the same time, as the tightness of the structure increases, breathing resistance increases, thereby affecting the user’s comfort while using the device. This may affect usage. The level of protection offered also may be contingent on the tightness of the fit of the device to the wearer’s face.
The committee was hampered in its work by the lack of reliable data in many areas of concern, in particular the routes and modes of influenza transmission. Consistent with its broader charge, the committee makes recommendations to DHHS on a research agenda ranging from the most fundamental aspects of infectious disease to more focused research opportunities in two major areas: (1) studies related to the epidemiological aspects of novel influenza viruses and (2) the design and development of reusable respirators and medical masks.
Recommendation 2: Determine Routes and Risks.
DHHS should expand pandemic influenza research to characterize and determine the routes of transmission and risks of disease associated with different levels and types of exposure.
Characterizing and determining the relative importance of different routes of influenza transmission (e.g., droplet, contact, aerosol) will allow for the design of more effective nonpharmacological interventions and personal protective equipment.
Recommendation 3: Short-Term Research Opportunities.
a. In the areas of design, materials, and processing technology, DHHS should sponsor and/or conduct research that will lead to understanding the efficacy of simple decontamination techniques (e.g., bleach, microwave radiation, or ultraviolet light) that could routinely be employed without having negative effects on respirator integrity.
Such factors as effectiveness of decontamination, impact on the reusability of the decontaminated device (e.g., filter efficiency, fit), processing cost, and ease of implementation (both in a large-scale setting and at home), including those related to environmental impact, should be considered in the research. These efforts could quickly lead to the identification of an
effective decontamination process that would extend the reusability of disposable N95 respirators beyond the scope already identified by the committee. The investigation of ozone, supercritical fluid extraction, and other advanced treatments might require a longer term research investment as they are newer technologies.
b. In the area of epidemiology, DHHS should sponsor and/or conduct research that will examine various forms of respiratory protection and their effectiveness under simulated conditions of use, including use by the public.
Such research would lead to a realistic understanding of the protection offered to healthy persons by placing a mask over someone who is ill and, conversely, the protection offered to a healthy person by wearing a mask (woven or nonwoven) or respirator in a contaminated environment.
c. DHHS should sponsor and/or conduct research on the risks associated with handling a respirator that has been used to protect against a viral threat. Such research should include determining whether and in which ways the exterior surface of a respirator becomes contaminated and the likelihood that it might harbor pathogenic microorganisms and thus serve as an agent of transmission of infection.
This research would improve understanding of the degree of external contamination on respiratory protective devices and the associated risk of transmission to the wearer, particularly during removal and redonning.
Recommendation 4: Long-Term Research Opportunities.
a. In the areas of design and materials technology, DHHS should sponsor and/or conduct research on the use of alternative materials, including bioactive fibers, for disposable N95 respirators to allow for extended use (e.g., polyester filter media) and higher durability elastomers for the straps.
An in-depth investigation of the use of alternative fibers for filters such as polyester, biocidal fibers, and shape-memory polymers could improve the fit and durability and lead to better methods of cleaning and decontamination. The effects of such fibers on the performance of the devices
(including filtration capacity and resistance to moisture), cost, ease of manufacturing, and disposability should be considered as part of the research. The various finishes used in the filters affect their performance. These finishes are proprietary; thus, the participation of manufacturers in the research would be critical. Similarly, DHHS should investigate the use of alternate materials (e.g., shape-memory polymers for improved fit) for the other components of the device—front and back layers, straps, and nose clips—so that they have improved fit and can better withstand cleaning and decontamination, resulting in longer usable life.
This research could lead to the identification of alternative fibers for the filters, new and better finishes for the filters, and newer materials for the other components of the device that would result in the reusability of disposable N95 respirators and medical masks. This effort should be carried out in close collaboration with manufacturers. The committee heard from NIOSH that in the event of an emergency, NIOSH would be more than willing to perform an expedited review in order to get such a product to market.
b. Given the durability of woven cloth masks, DHHS should sponsor and/or conduct an in-depth investigation of the engineering design of woven cloth masks to enhance their fit and assess their effectiveness to protect against influenza.
Specifically, research should focus on the material-process-structure-property relationships of woven cloth masks through incorporation of high-elongation stretch fibers (such as spandex) into fabrics containing the base fibers; investigation of a range of base or comfort fibers (e.g., cotton, polyester, polypropylene, blends) for the woven cloth masks; investigation of a range of structures of varying yarn densities, designs, plies, and manufacturing technologies (woven and knitted) for producing the woven cloth masks; and integration of disposable filtering media into multilayer clothmasks.
This comprehensive research agenda is expected to lead to the development of the specifications for an effective, reusable cloth mask that could be made readily available to the general public in the event of an influenza pandemic. Moreover, such reusable cloth masks may have a positive environmental impact (unlike disposables, which do not biodegrade in landfills).
c. Manufacturers should consider modifications to processing conditions, chemicals, and finishes to improve the electrostatic charge retention of respiratory protection filters.
One way to reuse the N95 filtering facepiece respirator is to make process modifications during manufacturing to improve the electrostatic charge retention of the filters (a parameter said to be critical for their efficacy) so that they can better withstand cleaning and decontamination, should such techniques prove to be effective. Research should therefore be directed at making modifications to current manufacturing processes to investigate the effects of various surface active finishes, charging (dwell) times, and materials on the electrostatic charge retention of the resulting devices. The effects of such process modifications on costs, production rates, and equipment modifications should be part of the research. Since manufacturing processes are proprietary, the participation of manufacturers is critical to executing this research.
This research could lead to the identification of processing conditions for the devices, especially the filters, and could permit reusability of disposable N95 respirators and medical masks.
d. DHHS should sponsor and/or conduct research on issues related to public education on and compliance with respiratory protection guidelines, including the importance of proper fit and the need for hand hygiene after handling respiratory protection.
Further research into the factors affecting an individual’s willingness and ability to comply with recommendations is vital to a complete infection control program. Both hospital and community studies on this topic will be important to understanding how best to maximize the benefit that may be seen from the use of nonpharmacological interventions for controlling pandemic influenza.
The threat of an influenza pandemic presents clear and unique challenges in that the timing, impact on populations, severity, and duration of a pandemic cannot be reliably predicted. In the absence of primary prevention, plans must be made to delay the entry of a novel pandemic virus into the population and to employ measures that prevent or slow transmission
of infection in both the healthcare and community environments. Respiratory protection is the last resort to control infectious spread. As has been stated throughout this report, many factors will influence the effectiveness of respiratory protection used by both healthcare workers and the public to mitigate potential infection in the event of an influenza pandemic. Experience with previous efforts to improve infection control in the hospital and elsewhere have demonstrated that the efficacy of an intervention alone does not guarantee its success. The best respirator or medical mask will do little to protect the individual who refuses, or misunderstands how and when, to use it correctly. Any public health effort aimed at extending the usefulness of existing devices must be delivered with clarity and truthfulness. The public is likely to forgive lack of knowledge but will not be willing to trust public health officials in the next instance if they have in any way been misinformed or misled.
CDC (Centers for Disease Control and Prevention). 2003. Interim Domestic Guidance on the Use of Respirators to Prevent Transmission of SARS. [Online]. Available: http://www.cdc.gov/ncidod/sars/respirators.htm [accessed January 23, 2006].
DHHS (Department of Health and Human Services). 2005. HHS Pandemic Influenza Plan. Washington, DC: DHHS.