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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu 2 Characteristics of Respirators and Medical Masks To prevent and control infectious respiratory diseases such as influenza, the first line of defense should be to prevent exposures by using control measures, such as isolation, quarantine, or restricting or closing group gatherings, and/or using local exhaust ventilation. When such measures are not feasible or fully effective, measures such as respiratory hygiene/cough etiquette and hand washing can be useful. Personal respiratory protection provides the last line of defense. In the workplace setting, the Occupational Safety and Health Administration (OSHA), in its respiratory protection standard Code of Federal Regulations Title 29, Part 1910.134, requires that businesses provide respirators to reduce employee exposure to respiratory hazards of all types, including dusts, fumes, and vapors; this standard extends to workers who will be in environments where exposure to tuberculosis is likely (OSHA, 1998). This chapter will discuss the prevention of dissemination of influenza organisms by two methods: (1) those meant to prevent inhalation by the user (i.e., respirator) and (2) those meant to protect persons around the user by limiting exhaled particles (e.g., mask). Many options are available for respiratory protection in the healthcare setting depending on the environment to which the user may be exposed and the probability of exposure. These devices have a variety of features. For example, they may supply clean, breathable air from a compressed air source or filter the contaminated air, they may cover half or the entire face,
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu they may have variable filter composition, and they may have differing modes of operation (e.g., powered vs. nonpowered). The performance of a respirator or medical mask depends on the efficiency of the filter (how well it is able to collect airborne particles) and fit (how well it prevents leakage around the facepiece). FILTRATION THEORY OF AIRBORNE PARTICLES Media used for the filtration of airborne particles do not work by the same principles as those used for the filtration of liquids. Filters used in respirators and medical masks must allow the user to breathe and thus cannot clog when particles adhere to their fibers. Respirator and medical mask filters are typically composed of mats of nonwoven fibrous materials, such as wool felt, fiberglass paper, or polypropylene (see Box 2-1). The material creates a tortuous path, and various mechanisms result in the adhesion of particles to the fibers without necessarily blocking the open spaces, still allowing air to flow easily across the filter (Revoir and Bien, 1997). This chapter will discuss three mechanisms of removing particles from the airstream: inertial impaction, diffusion, and electrostatic attraction (see Figure 2-1). Mechanisms for removing large particles differ from those for small particles. The model postulates that inertial impaction is effective for aerosol particles that are approximately 1 µm and larger. Such particles have enough inertia that they cannot easily flow around the respirator fibers. Instead of flowing through the filter material, the large particles deviate from the air streamlines and collide with the fibers and may stick to or be caught in them. For much smaller particles—those that are 0.1 µm and smaller—diffusion is regarded as an effective filtration mechanism. Brownian motion—the process by which the constant motion of oxygen/nitrogen molecules causes collisions between particles—results in a “wandering” pathway. The complex path that is followed by the small particles increases the chance that they will collide with the filter fiber and remain there. Another efficient method of capturing both large and small particles from the airstream is said to be electrostatic attraction, in which electrically charged fibers or granules are embedded in the filter to attract oppositely charged particles from the airstream. The attraction between the oppositely charged fibers and particles is strong enough to effectively remove the particles from the air. The first electrostatic filters used resins
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu BOX 2-1 Materials and Components Used in Respirators and Medical Masks The filtering materials of respirators and medical masks are typically nonwoven. These materials, initially using natural fibers, came into greater prominence with the introduction of synthetic thermoplastics, particularly polypropylene, about 40 years ago. Spun-bonded polypropylene is a fabric or structure in the category of nonwoven textile materials. The salient advantage of nonwoven technology is the ability to produce fabrics or structures at significantly lower cost than the older fabric-generating techniques of weaving or knitting of spun yarns. Additional important advantages are the versatility of the process and the products in terms of properties and uses. There has been ongoing development of and increasing sophistication in spun-bonded, and the related melt blown, technologies, which have made these materials the optimal choice in many applications. Polypropylene is one of five major commodity plastic resins now produced in large quantities in many countries. It is readily converted into spun-bonded fabric and structures with a very wide range of properties. Some of the parameters that can be varied include fiber thickness (down to micron or submicron diameters), density of fibers per unit area or volume, density of bond points, and average orientation of fibers. For filtration and trapping of aqueous particles (as in respirators and medical masks), polypropylene fiber surfaces require modification to render them more hydrophilic (water attracting) because polypropylene is inherently hydrophobic (water repelling). Several methods are known to impart the necessary degree of hydrophilicity to the surface. A process in which a droplet-attracting electric charge is applied to the surface has also been described, but it is not clear that such a charge could be maintained during storage of the respirator or mask, and the charge would dissipate with exposure to air with any degree of humidity. These materials and processes have produced a viable material whose low cost permits a disposable, one-use culture to prevail in industrialized countries. Spun-bonded polypropylene masks have completely supplanted the woven cotton fabric masks previously used in the United States and predominate in the filtration components of commonly used respirators.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu FIGURE 2-1 Filtration mechanisms. added to natural wool fibers to retain an electrostatic charge. This addition enhanced the efficiency many times over the basic wool material. However, the efficiency of resin electrostatic filters is degraded when they are exposed to airborne oil mists and other materials that shield the electrostatic charge. Manufacturers have been able to overcome this issue by incorporating synthetic plastic fibers, such as polypropylene (see Box 2-1), which are said to be capable of holding a sufficiently strong electrostatic charge (electret) to effectively resist the shielding effects of oil. Once particles are captured by a filter, they are held tightly to the fibers through van der Waals bonding and other forces, thus making it difficult for captured particles to escape. Filters generally become more efficient with loading (i.e., the adhesion of additional particle to the filter fibers). This increase in efficiency is the result of the increased number of collection points that are created by the particles that have already adhered to the filter fibers. However, increased loading becomes a problem when enough particles have been captured to begin to block the open spaces of the woven or nonwoven network. This blockage results in a buildup in pressure drop
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu and an increase in resistance that eventually makes it difficult to breathe while wearing the respirator. Heavy loading of filters may also increase the ability to dislodge particles that have already been captured. Very little research has been conducted on the characteristics of filters in relation to loading. However, the relatively clean environment in healthcare facilities and the limited time of use of a respirator suggest that filter clogging will rarely become an issue. Loading might be of some concern for use in areas that have considerably dirtier air than healthcare facilities. More information about the efficiency of respirator filters can be found later in this chapter under the subsection “Filters.” PROPERTIES OF RESPIRATORS A respirator is a personal protective device that is worn on the face, covers at least the nose and mouth, and is used to reduce the wearer’s risk of inhaling hazardous airborne particles (including dust, infectious agents, gases, or vapors). Respirators sold in the United States are tested and certified by the National Institute for Occupational Safety and Health (NIOSH). Employers covered by the Occupational Safety and Health Act or by the Mine Safety and Health Act are required to provide their employees with respirators that have been certified for use by NIOSH. The OSHA respiratory protection standard 1910.134 regulates the use of respirators (OSHA, 1998). It requires the employer to develop and implement a written respiratory protection program with required worksite-specific procedures and elements for respirator use that include procedures for selecting respirators; fit-testing methods for tight-fitting respirators; medical evaluation of employees required to use respirators; procedures and schedules for cleaning, disinfecting, storing, inspecting, repairing, discarding, and otherwise maintaining respirators; procedures to ensure adequate air quality, quantity, and flow of breathing air for atmosphere-supplying respirators; procedures for proper use of respirators in routine and reasonably foreseeable emergency situations; training of employees in the proper use and maintenance of respirators, including putting on and removing them and any limitations on their use; and procedures for regularly evaluating the effectiveness of the program.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu The program must be overseen by a suitably trained program administrator. The program must be updated as necessary to reflect any changes in workplace conditions that affect respirator use. Types of Respirators Respirators can be categorized as air-purifying or atmosphere-supplying (Ha’eri and Wiley, 1980). Air-purifying respirators include those that employ filters to remove airborne particulate matter (such as N95 filtering facepiece respirators), those that employ an adsorbent to remove hazardous vapors and gases (half-facepiece with chemical cartridges or canisters), and those that combine a filter and adsorbent to remove particulate matter, gases, and vapors (cartridge or canister with particulate-removing filter). Per the NIOSH respirator selection logic, air-purifying respirators cannot be used in atmospheres that lack a normal amount of oxygen (approximately 20 percent) or that contain sufficiently high concentrations of contaminants to be classified as immediately dangerous to life or health (NIOSH, 2004). These air-purifying respirators can be either nonpowered or powered. Nonpowered respirators depend on the wearer to draw air in through the filters or cartridges, and thus there is negative pressure1 inside the facepiece during inhalation. Powered air-purifying respirators (PAPRs) use a blower to draw air through the filter and deliver it to the wearer, thereby eliminating airflow resistance to the wearer. PAPRs that are tight fitting or have a hood/helmet design are expected to provide higher levels of protection because the pressure inside the respirator is likely to remain positive, and certainly less negative than a non-PAPR air-purifying respirator (Ha’eri and Wiley, 1980; ANSI, 2001). Although rarely used in healthcare settings, air-supplying respirators can be classified into (1) self-contained breathing apparatus (SCBA) for use by emergency responders or in chemical, biological, radiological, and nuclear and oxygen-deficient environments2 and (2) airline respirators designed to deliver clean breathing air to hoods, helmets, and full- and half-facepiece masks. The air sources include a compressed gas cylinder, plant 1 Pressure inside the facepiece drops when the wearer inhales. 2 An additional type of SCBA is an “industrial-only” version that does not necessarily resist damage or penetration by chemical warfare agents.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu breathing air, or a low pressure pump. Supplied air respirators are most useful against contaminants that are not easily removed by filters or sorbents owing to their physical nature or concentration. The correct choice of respirator for use in a particular working environment depends on which contaminants may be present as well as their concentrations (Herrick and Demont, 1994). NIOSH’s respirator decision logic assists in choosing the type of respirator to use in a specific industry or working environment (NIOSH, 2004). Facepieces The facepieces of negative-pressure respirators include filtering facepieces and elastomeric half and full facemasks that use replaceable filter elements (BLS, 2002). N95 filtering facepiece respirators and half-mask elastomeric respirators cover the wearer’s nose and mouth, whereas full facemasks also protect the eyes. PAPRs can be equipped with standard half or full facepieces, a loose-fitting facepiece, or a hood or helmet that can be equipped with or without a neck seal. Filters Respirator particulate filters are characterized as P (oil proof; can survive oil exposure for more than one work shift), R (oil resistant; can be used for oil exposure in one shift), and N (not oil resistant; used for oil-free atmospheres). P and R series filters can also be used in oil-free environments. Gas/vapor respirators use sorbent cartridges approved for specific chemicals. Combinations of particulate filters and chemical cartridges are used when protection from exposure to both types of contaminants is needed in normal work environments (NIOSH, 2004). Testing and certification regulations for respirators can be found in 42 Code of Federal Regulations Part 84, most recently updated in June 1995. These regulations specify the maximum acceptable level of breathing resistance for both inhalation and exhalation and the necessary level of filter performance under test conditions. To be NIOSH-certified, tests of respirator filters evaluate the collection efficiency of the filter material using relatively small particles (0.3 µm, which has been found to be the most penetrating size). The effects of loading, temperature and humidity, and airflow are also evaluated. Filters can be certified for a range of efficiency
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu classes (e.g., 95, 99, or 100 percent) as well as for their ability to withstand degradation due to loading or oil mist exposures. N95 filters are not permitted to have more than 5 percent of the challenge aerosol concentration penetrate the filter and would be expected to have less aerosol penetration with either larger or smaller particles than the size used in certification testing. As these tests are conducted at very high flow rates, it is expected that these filters will collect all particle sizes with efficiencies greater than 95 percent under normal conditions of use. N95 Respirators Most filtering facepiece respirators are manufactured only in the N95 configuration. For healthcare settings, the term “N95 respirator” has become synonymous with N95 filtering facepiece respirators (as opposed to those that have reusable facepieces but employ N95 filters). (See Figure 2-2.) Filtering facepiece respirators are part of a family of negative-pressure respirators, meaning the pressure inside the facepiece becomes negative FIGURE 2-2 Filtering facepiece respirator. NOTE: An example of a filtering facepiece respirator held to the user’s head with two elastomeric straps. The respirator also has a pliable metal nosepiece to allow for the user to adjust the fit at the nose.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu when the wearer inhales a breath of air. During the negative-pressure period (about half the time a respirator is worn), any leakage along the sealing surface of the face will allow hazardous contaminants to bypass the filtering element and be inhaled. For this reason, wearers of negative-pressure respirators must be clean-shaven as facial hair has been shown to interfere with the sealing edge of the respirator, and they must be fit-tested to ensure that the respirator properly seals to the face. The need for periodic fit-testing is outlined in ANSI consensus standard Z88.2 and is also an OSHA requirement. While some groups such as the Infectious Disease Society of America3 have spoken out against the need for fit-testing healthcare workers in tuberculosis environments, not enough is known about the transmission of influenza to make a similar comparison, and other research contradicts that recommendation (Lee et al., 2004). Fit-testing methods include both qualitative and quantitative tests; they are specified in OSHA regulation 1910.134 and can also be found in the American National Standards Institute standard ANSI Z88.10. It is hypothesized that most of the contaminants enter through faceseal leakage rather than filter penetration. Published studies conducted in laboratory and workplace environments have examined the total inward leakage of respirators worn by subjects who have been properly fit-tested and trained with a fully functional N95 filtering facepiece. These studies have found that 95 percent of the subjects had at least 80 percent to 90 percent protection from the test particulate contaminants. In other words, the respirator allowed no more than 10 percent to 20 percent of the contaminants to pass through to the wearer (CDC, 1998; Coffey et al., 1999). Nicas notes, however, that achieving a fit test is not always indicative that the respirator will perform appropriately under ongoing job stress (Nicas et al., 2004). By contrast, the ability of an individual wearer to obtain good facepiece fits is far more varied and is a function of the facial dimensions of the wearer, the training received by users to ensure that the device is properly placed on the face each time the respirator is donned, and how closely the 3 The Infectious Disease Society of America defines itself as an organization that “represents physicians, scientists and other health care professionals who specialize in infectious diseases. IDSA’s purpose is to improve the health of individuals, communities, and society by promoting excellence in patient care, education, research, public health, and prevention relating to infectious diseases.” It is not a recognized authority on fit-testing.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu device matches the size and shape of the wearer’s face. Coffey et al. (2004) have demonstrated that subjects who wear most N95 filtering facepieces without prior fit-testing fail to achieve the expected levels of protection and that persons passing a qualitative or quantitative fit test will achieve the expected level of protection. Some N95 filtering facepiece respirators have exhalation valves placed near the mouth of the wearer. Exhalation valves bypass the filter media and significantly reduce the effort required to exhale and also increase the wearer’s comfort as there is less heat and moisture buildup. A disadvantage of this configuration is that if a nonsymptomatic, but infectious wearer is exhaling a virus or other pathogen, the virus or pathogen may bypass the filter, be emitted to the outside environment, and possibly infect individuals in the immediate vicinity (CDC, 2003). As with any type of respirator, wear time affects the performance of the N95. The longer the respirator is worn, the more particulate loading and moisture buildup from exhaled air occurs, with possible obstruction of breathing. In addition, the more the filtering facepiece respirator is taken off and redonned, the greater the odds that it may be deformed creating a suboptimal fit and increasing leakage. PROPERTIES OF MEDICAL MASKS A mask used in a healthcare setting is a disposable face covering designed to fit loosely over the user’s nose and mouth. Although there are some hybrid mask/respirators (see discussion later in this chapter), masks are not respirators, and they undergo a different regulatory and certification process. The loose fit of most medical masks leaves gaps that could allow substantial contaminant leakage into and from the mask. Food and Drug Administration (FDA) regulatory requirements do not address the fit of medical masks, which can make the total filtration efficiency of questionable value (CDRH, 2004). Masks approved by FDA for medical use are designed to be worn by an infected person, healthcare worker, or member of the public to reduce transfer of body fluids that may spread infection. Medical masks may be used as barriers against disease transmission by fluids, especially blood, and some large droplets, and they are designed to prevent release to the environment of large droplets generated by the wearer (see Table 2-1). They are not designed or approved for the purpose of protecting the wearer against entry of infectious aerosolized particles potentially
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu TABLE 2-1 Comparison of Respirators and Medical Masks N95 Filtering Facepiece Respirator Medical Mask Intended use Reduce wearer’s inhalation exposure to certain airborne particles < 100 µm To protect both the surgical patient and operating personnel from expired respiratory droplets from the wearer Use limitations Subject to considerations of hygiene, damage, and increased breathing resistance One-time use Use may extend beyond 8 hours only if it is demonstrated that extended use will not degrade filter efficiency and total mass loading of filter is less than 200 mg Certification requirements Certified by NIOSH under 42 CFR 84 FDA reviews 510(K) submission and clears for marketing Filter elements Nonreplaceable Nonreplaceable Filter efficiency 95% Particle and bacterial filtration efficiency quality indicator Testing aerosol and particle size Sodium chloride test aerosol with a mass median aero- dynamic diameter particle of about 0.3 µm Polystyrene latex sphere test aerosol approx 0.1 µm and Staph. aureus filtration test, per ASTM standard (PFE) Airflow rate 85 L/min 28 L/min Test aerosol Charge neutralized test aerosol Unneutralized test aerosol Preconditioning Preconditioning at 85% relative humidity and 38°C for 24 hrs No preconditioning Faceseal fit Designed to fit tightly to face Annual fit-test required Not designed to fit to face Fit check requirements Required with each use Not designed for fit check Available sizes Some models available in three sizes Only one facepiece size generally available. Tends to produce more leakage on small facial sizes Approximate cost $0.70–$2.34 each $0.15 each SOURCE: National Personal Protective Technology Laboratory (2006).
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu surrounding the wearer and his or her mask (See Table 2-2). As noted in Chapter 1, there are two types of medical masks: surgical and procedure masks. Surgical masks, which were originally designed to protect the operating field from contaminants generated by the wearer, are of two main types: (1) flat-pleated or duck-billed in shape, conforming to the bridge of the nose with a flexible piece, affixed to the head with two ties and (2) premolded, conforming to the bridge of the nose with a flexible piece, and adhering to the head with a single elastic. In the context of this report, unless otherwise specified, a surgical mask has demonstrated filtration efficiency and fluid resistance required by FDA, or the manufacturer has demonstrated that the performance of the mask is as good as or better than any other mask it currently has on the market. TABLE 2-2 Functions Performed by Respirators and Masks Currently Available Masks Function Respirator (all NIOSH- approved N95 or better) Blocks particles < 100 µm from being inhaled Surgical N95 Blocks particles < 100 µm from being inhaled Reduces the transfer of respiratory droplets to others Blocks blood or other potentially infectious materials from reaching the wearer’s skin, mouth, or mucous membranes Keeps droplets and larger particles from being inhaled. Requires filtration of all air reaching the mouth/nose for 5 µm particles and larger Medical mask Reduces the transfer of respiratory droplets to others Blocks blood or other potentially infectious materials from reaching the wearer’s skin, mouth, or mucous membranes Keeps droplets and larger particles from being inhaled. Requires filtration of all air reaching the mouth/nose for 5 µm particles and larger Woven cotton (or other fabric masks) and improvised protection Reduces the transfer of respiratory droplets to others
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu Procedure masks, designed to be used in the same way as surgical masks, are flat-pleated or duck-billed in shape and fasten to the head with ear loops. Other masks, including laser, isolation, and dental masks, also possess these characteristics. The intended use of medical masks is to maintain a sterile environment by preventing the spread of contaminants originating from the user, such as in saliva or respiratory secretions produced on exhalation. In addition, a surgical mask can protect the user from fluids that may splash during medical procedures. Any mask intended to be worn by a healthcare worker is regulated by FDA. However, FDA does not ask manufacturers to test the devices with any particular disease or disease-causing agent (pathogen). Instead, the masks are tested using a 0.1 µm polystyrene latex sphere aerosol test and Staphylococcus aureus filtration test in accordance with American Society for Testing and Materials (ASTM) standards (see Table 2-1 and discussion later in this chapter) (ASTM, 2001; ASTM , 2003). Both types of medical masks come in a variety of forms, with a spectrum of “protective” features. Typically, a fluid-resistant disposable medical mask has multiple layers or plies of different nonwoven fabric materials that form a composite material laminate that is used for the nose and mouth section of the mask (Maturaporn, 1995). For example, a three-layered laminate structure is pleated and sized to cover the wearer’s nose and mouth. The innermost layer (the first ply) comes in contact with the wearer’s face and is made of nonwoven, airlaid4 paper material that is resistant to liquid and designed to be soft. It is intended to prevent facial hair, perspiration, and saliva from interfering with or exiting the facemask. The second layer is made of nonwoven, liquid-resistant, melt blown, polypropylene material designed to act as a barrier against bacteria, body fluids, and particulate contaminants. The outermost layer (the third ply) is made of nonwoven, liquid-resistant, thermobond, polypropylene fabric designed to be the first contact filter barrier layer against body fluids and liquid particulate contaminants from outside the wearer’s medical mask. The three-ply structure 4 A process of manufacturing nonwoven material by which the fibers are fed into an airstream and from there to a moving belt or perforated drum, where they can form a randomly oriented web.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu is fused through ultrasonic heat-sealing. The medical mask is secured to the wearer’s head and face by either ear loops or head ties. The medical mask may have a nosepiece made of malleable aluminum wire. Masks with splash visors have an attached antifog-treated plastic shield. While some high-performance surgical masks can exceed 99 percent filtration efficiency at 0.1 µm, there is no pass/fail criteria for filtration. Rather, test data are an indicator of quality, and masks are required to perform at least as well as other masks currently on the market. The Association of Perioperative Registered Nurses suggests that surgical masks should filter bacteria at least 0.3 µm in size for regular use and 0.1 µm in size for use in laser surgery, or they should provide 90 percent to 95 percent bacterial filtration efficiency (AORN, 2005). While there is no method to test the fit of surgical masks, fit of any form of respiratory protection is important in preventing airborne disease. As most surgical masks are not designed to fit tightly to the face, air will take the path of least resistance and bypass the mask surface if there is a gap between the mask and the face. When placed on an infectious patient, a medical mask may contain the patient’s respiratory secretions and reduce the spread of particles to others. Likewise, when a patient is not wearing a medical mask, medical personnel may choose to don a mask to limit mucous membrane contact with infectious droplets. There is no evidence, however, that mask use by either infectious patients or healthcare personnel will prevent influenza transmission (CDC, 2005). In the United States, medical masks have been used in healthcare settings as a method of limiting exposure to infectious droplets; however, they are not commonly used in community settings (see Chapter 3 for further discussion). Medical Mask/N95 Filtering Facepiece Respirators Respiratory protection that combines the properties of surgical masks and respirators is known as a medical mask/N95 filtering facepiece respirator. These devices have the ability to protect against inhaled particles and also resist fluids and limit the dispersion of exhaled properties. These devices are regulated by both NIOSH and FDA. Effectiveness of Surgical Masks Few studies have demonstrated the efficacy of surgical masks in protecting the sterile field. The emphasis in the development of surgical masks
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu to date has been on protecting the patient during surgery, and thus efforts to improve such masks have focused on filtering efficiency, which has been measured in disparate ways (Belkin, 1997). The collection efficiency of mask filters is extremely variable, with studies showing differing penetration ranges depending on the size of the particles and the test methods used (Cooper et al., 1983b; Tuomi, 1985; Brosseau et al., 1997; McCullough et al., 1997; Willeke and Qian, 1998). Two studies indicate that wearing a mask does not influence the incidence of infection in surgical wounds (Orr, 1981; Tunevall, 1991). One study has shown that minimizing faceseal leakage by wearing the mask under headgear prevented wound contamination (Ha’eri and Wiley, 1980). Non-Surgical Masks and Alternative Materials Several gauze or woven cotton masks are available in addition to FDA-approved medical masks. Masks of this design were used extensively during the outbreak of Severe Acute Respiratory Syndrome (SARS) in Asia (see Chapter 3). In addition, in emergency settings, workers and the public have sometimes protected their airways with readily available materials (such as sheet or towel materials) or used nonapproved disposable facemasks available at hardware stores as a means of respiratory protection. Early reusable surgical masks were made of woven linen, which only redirected exhaled air away from the surgical wound. Cloth surgical masks, sometimes made of cheesecloth (McNett, 1949), were replaced in the early 1960s with the synthetic materials described earlier that also provide bacterial filtration and improved filtration efficiency (See Box 2-2). Limited testing with mannequins has shown that these materials can reduce concentrations of aerosol particles and certain water-soluble gases and vapors at pressure drops acceptable for respiratory protection during accident conditions (Cooper et al., 1983a). When such materials are used in combination with improvised techniques to improve the face fit (e.g., nylon hosiery), leakage can be reduced (Cooper et al., 1983b). Tests conducted in animals have shown that tightly fitted six-layer gauze masks reduce the incidence of contamination with tuberculosis bacilli by 90 percent to 95 percent (Lurie and Abramson, 1949). However, regulatory standards require that a mask should not permit blood or other potentially infectious materials to pass through to or reach the wearer’s skin, eyes, mouth, or other mucous membranes under normal conditions of use and for the duration of time that the protective equipment will be used (OSHA, 1992).
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu BOX 2-2 The Engineering Design of Textile Structures: Material-Process-Structure-Property Relationships The engineering design of textile structures, such as fabrics for parachutes, apparel, facemasks, and geotextiles, is a complex task. The task is made even more complex because of the significant interactions between the design parameters associated with the materials and structures that ultimately determine the properties of the resulting textiles. For example, the linear density of the fibers used to make the yarn in the fabric and the thread density (i.e., the number of threads per unit area in the fabric) significantly influence the tensile strength, air permeability, and flexural rigidity of the resulting woven fabric. Thus, if one tries to increase the fabric tensile strength by increasing the thread density, it will make the fabric stiffer and reduce its air permeability. Consequently, the engineering design of fabrics to realize desired end-use properties requires numerous trade-offs and becomes more complicated if the design has to accommodate additional constraints imposed by the manufacturing processes (e.g., weaving, knitting, braiding, and nonwovens). Thus, the engineering design of textile structures involves an in-depth assessment of the materials-process-structure-property relationships of such structures; it also calls for a structured approach to realize the optimal design while meeting the constraints imposed by the materials, structures, and processes. A structured framework or approach for the engineering design of textile structures involves understanding the specific requirements for the product (e.g., functionality, wearability, comfort, maintainability, durability, and affordability), translating them into measurable properties, identifying appropriate materials, selecting manufacturing technologies, and implementing processing parameters to achieve the specific requirements in the desired product (Rajamanickam et al., 1998). Thus, in the case of a respiratory protection against influenza, the first step would be to identify the key requirements, such as functionality (protection against virus), comfort, fit, and reusability (cleaning and decontamination); these subjective requirements are translated into appropriate objective properties of the mask that can be measured, such as filtration capability. The properties lead to the specific design for the medical mask or respirator—a structure meeting the requirements of filtration, fit, comfort and decontamination. These properties in the design are achieved through the appropriate choice of materials, such as cotton, polyester, polypropylene, blends, bioactive fibers, and fabrication technologies such as weaving, knitting, and nonwovens.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu Because it is not clear that woven cloth masks can meet either FDA or NIOSH standards, and without better testing and more research, cloth masks or improvised protection generally have not been recommended in the literature as effective personal protective devices against infection. BEHAVIORAL COMPLIANCE ISSUES RELATED TO RESPIRATORY PROTECTION The committee was asked to consider educational and behavioral compliance issues as a part of its recommendations. 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 to wear it or who does not use it correctly. Research suggests that noncompliance with respiratory protection requirements is common and implementing new practices is difficult (Seto, 1995). Tokars and colleagues (2001) conducted a large observational study in two hospitals that had outbreaks of multidrug-resistant tuberculosis. They found that compliance with appropriate respiratory protection requirements varied from 42 percent to 97 percent. Similarly, Kellerman and colleagues (2001) found low compliance rates among hospital staff, family, and friends visiting pediatric patients with known or suspected tuberculosis. In this study, compliance with the use of the correct respiratory protection device occurred 73 percent of the time, and the device was used correctly only 76 percent of that 73 percent. Data from the SARS experience in Toronto are also of concern. Loeb and colleagues (2004) found that 9 out of 32 (28 percent) nurses entering a SARS patient’s room did not consistently wear appropriate respiratory protection. None of these studies explored the reasons why specific individuals chose not to wear respiratory protection. Their findings are nevertheless important, as they highlight the fact that noncompliance with respiratory protection guidelines needs to be more closely examined. SUMMARY AND CONCLUSIONS The major differences between medical masks and respirators are their intended uses and levels of protection (Tables 2-1 and 2-2). A medical mask is intended to protect others from large droplets exhaled or released by the wearer. It is also designed to protect the wearer’s respiratory tract
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu from splashes of body fluids that may unexpectedly occur in the clinical setting. In contrast, a respirator is designed to protect the wearer from hazardous contaminants in the air. Most N95 filtering facepiece respirators are not designed to protect the wearer from splashes of body fluids. However, some N95 filtering facepiece respirators (called surgical N95 respirators) have this additional feature and are certified by NIOSH as well as regulated by FDA. Medical masks and N95 filtering facepiece respirators are considered disposal devices and are not designed for either extended use or reuse after cleaning and disinfection. When selecting a personal protective device for healthcare workers and the public for protection against an airborne infection, an N95 filtering facepiece is likely to be both the least expensive and the most widely available NIOSH-certified respirator for such protection. A full facepiece airpurifying respirator, a PAPR, and an airline respirator are examples of alternatives with increasing levels of protection for the wearer. However, some of these alternatives may be considered prohibitive in terms of cost, training required, ease of use, and/or availability in sufficient quantities to protect healthcare workers and the public in the event of a pandemic. The next chapter describes what is known about the use and reuse of respiratory protective devices in the context of an influenza pandemic. REFERENCES ANSI (American National Standards Institute). 2001. ANSI Z88.2—American National Standard for Respiratory Protection. Washington, DC: ANSI. AORN (Association of Operating Room Nurses). 2005. Recommended Practices for Surgical Attire. [Online]. Available: http://www.findarticles.com/p/articles/mi_m0FSL/is_2_81/ai_n9773853/print [accessed March 17, 2006]. ASTM (American Society for Testing and Materials International). 2001. Standard Test Method for Evaluating the Bacterial Filtration Efficiency (BFE) of Medical Face Mask Materials, Using a Biological Aerosol of Staphylococcus Aureus. West Conshohocken, PA: ASTM. ASTM. 2003. Standard Test Method for Determining the Initial Efficiency of Materials Used in Medical Face Masks to Penetration by Particulates Using Latex Spheres. West Conshohocken: ASTM. Belkin NL. 1997. The evolution of the surgical mask: Filtering efficiency versus effectiveness. Infection Control and Hospital Epidemiology 18(1):49–57. BLS (Bureau of Labor Statistics). 2002. News. Washington, DC: U.S. Department of Labor. Brosseau L, McCullough N, Vesley D. 1997. Bacterial survival on respirator filters and surgical masks. Journal of the American Biological Safety Association 2:232–247.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu CDC (Centers for Disease Control and Prevention). 1998. Laboratory performance evaluation of N95 filtering facepiece respirators, 1996. Morbidity and Mortality Weekly Report 47(48):1045–1049. CDC. 2003. Cluster of severe acute respiratory syndrome cases among protected healthcare workers—Toronto, Canada, April 2003. Morbidity and Mortality Weekly Report 52(19):433–436. CDC. 2005. Interim Guidance About Avian Influenza A (H5N1) for U.S. Citizens Living Abroad. Atlanta: CDC. CDRH (Center for Devices and Radiological Health). 2004. Guidance for Industry and FDA Staff: Surgical Masks—Premarket Notification [510(k)] Submissions. Rockville, MD: Food and Drug Administration. Coffey CC, Campbell DL, Zhuang Z. 1999. Simulated workplace performance of N95 respirators. American Industrial Hygiene Association Journal 60:618–624. Coffey CC, Lawrence RB, Campbell DL, Zhuang Z, Calvert CA, Jensen PA. 2004. Fitting characteristics of eighteen N95 filtering-facepiece respirators. Journal of Occupational and Environmental Hygiene 1(4):262–271. Cooper DW, Hinds WC, Price JM. 1983a. Emergency respiratory protection with common materials. American Industrial Hygiene Association Journal 44(1):1–6. Cooper DW, Hinds WC, Price JM, Weker R, Yee HS. 1983b. Common materials for emergency respiratory protection: Leakage tests with a manikin. American Industrial Hygiene Association Journal 44(10):720–726. Ha’eri G, Wiley A. 1980. The efficacy of standard surgical face masks: An investigation using “tracer particles.” Clinical Orthopaedics and Related Research 148:160–162. Herrick R, Demont J. 1994. Industrial hygiene. In: Rosenstock L, Cullen MR, eds. Textbook of Clinical Occupational and Environmental Medicine. 1st edition. Philadelphia, PA: WB Saunders Company. Pp. 169–193. Kellerman SE, Saiman L, San GP, Besser R, Jarvis WR. 2001. Observational study of the use of infection control interventions for Mycobacterium tuberculosis in pediatric facilities. Pediatric Infectious Disease Journal 20(6):566–570. Lee K, Slavcev A, Nicas M. 2004. Respiratory protection against Mycobacterium tuberculosis: Quantitative fit test outcomes for five type N95 filtering-facepiece respirators. Journal of Occupational and Environmental Hygiene 1:22–28. Loeb M, McGeer A, Henry B, Ofner M, Rose D, Hlywka T, Levie J, McQueen J, Smith S, Moss L, Smith A, Green K, Walter SD. 2004. SARS among critical care nurses, Toronto. Emerging Infectious Diseases 10(2):251–255. Lurie MB, Abramson S. 1949. The efficiency of gauze masks in the protection of rabbits against the inhalation of droplet nuclei of tubercle bacilli. American Review of Tuberculosis 59:1–9. Maturaporn T (Inventor). 1995. Disposable Face Mask with Multiple Liquid Resistant Layers. U.S. Patent. McCullough NV, Brosseau LM, Vesley D. 1997. Collection of three bacterial aerosols by respirator and surgical mask filters under varying conditions of flow and relative humidity. Annals of Occupational Hygiene 41(6):677–690. McNett EH. 1949. The face mask in tuberculosis. American Journal of Nursing 49(1):32–36.
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Reusability of Facemasks During an Influenza Pandemic: Facing the Flu Nicas M, Harrison R, Charney W, Borwegan B. 2004. Respiratory protection and severe acute respiratory syndrome. Journal of Occupational & Environmental Medicine 46(3):195–197. NIOSH (National Institute for Occupational Safety and Health). 2004. NIOSH Respirator Selection Logic 2004, Chapter III: Respirator Selection Logic Sequence. [Online]. Available: http://www.cdc.gov/niosh/docs/2005-100/chapter3.html [accessed March 17, 2006]. NPPTL (National Personal Protective Laboratory). 2006. Comparison of Respirators and Surgical Masks. Given to the Committee. March 6. Orr NW. 1981. Is a mask necessary in the operating theatre? Annals of the Royal College of Surgeons of England 63(6):390–392. OSHA (Occupational Safety and Health Administration). 1992. OSHA Preambles, Bloodborne Pathogens. (29 CFR 1910.1030) Section IX. Summary and explanation of the standard. Occupational Safety and Health Administration. [Online]. Available:http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=PREAMBLES&p_id=811 [accessed March 17, 2006]. OSHA. 1998. 1910.134 Respiratory protection. Federal Register 63(5):1270–1300. Rajamanickam R, Park S, Jayaraman S. 1998. A structured methodology for the design and development of textile structures in a concurrent engineering environment. Journal of the Textile Institute 89(3):44–62. Revoir WH, Bien CT. 1997. Respiratory Protection Handbook. New York: Lewis Publisher. Seto WH. 1995. Staff compliance with infection control practices: Application of behavioral sciences. Journal of Hospital Infection 30(1):107–115. Tokars JI, McKinley GF, Otten J, Woodley C, Sordillo EM, Caldwell J, Liss CM, Gilligan ME, Diem L, Onorato IM, Jarvis WR. 2001. Use and efficacy of tuberculosis infection control practices at hospitals with previous outbreaks of multidrug-resistant tuberculosis. Infection Control and Hospital Epidemiology 22(7):449–455. Tunevall TG. 1991. Postoperative wound infections and surgical face masks: A controlled study. World Journal of Surgery 15(3):383–387. Tuomi T. 1985. Face seal leakage of half masks and surgical masks. American Industrial Hygiene Association Journal 46(6):308–312. Willeke K, Qian Y. 1998. Tuberculosis control through respirator wear: Performance of National Institute for Occupational Safety and Health–regulated respirators. American Journal of Infection Control 26(2):139–142.
Representative terms from entire chapter: