Use and Reuse of Respiratory Protective Devices for Influenza Control
As mentioned in Chapter 1, barrier precautions such as masks and respirators are regarded as the last line of defense against influenza transmission. Vaccination, early detection, isolation and antiviral medications (as prophylaxis or treatment), and administrative measures (e.g., restricting visitors, educating patients and staff, and confining healthcare workers assigned to an outbreak unit) are known to be effective control measures (Bridges et al., 2003). However, primary prevention strategies, such as vaccines and antiviral prophylaxes, may be unavailable or initially limited in quantity and availability, depending on the influenza strain. Thus, public health officials may have to recommend respiratory protection in the form of medical (surgical or procedure) masks, respirators, or both to protect healthcare workers and the public against an influenza pandemic, and there may still be a problem if supplies of disposable medical masks and respirators are insufficient. Thus, the Department of Health and Human Services (DHHS) asked the Institute of Medicine (IOM) to consider reuse of masks and respirators designed to be disposable through design modifications, cleaning and decontamination, or other means.
In this chapter, the committee discusses existing guidance on the use of respiratory protection to control infectious spread, describes the problems posed by reuse, reviews what is known about the use of disposable medical masks and respirators in comparable situations, and addresses the implications for reuse of such devices.
The committee does not distinguish between use by healthcare workers or by the public but recognizes that, in general, the risk of exposure is likely to be significantly higher among healthcare workers. The committee does note that the Occupational Safety and Health Administration (OSHA) requires employers of healthcare workers to have a respiratory protection program in place that provides greater opportunities for proper training in the continued use, disposal, and decontamination of medical masks and respirators. The committee also recognizes that in the event of pandemic influenza, many sick individuals will be treated at home; thus, caregivers and other family members will be in close proximity to infected individuals and will face much the same risks of exposure as those experienced by healthcare workers. The committee also notes that use of some respiratory protection may be limited to adults with normal lung function; children, those with underlying breathing difficulties, and those who are otherwise difficult to fit (because of facial hair or facial size) may not be able to wear respiratory protection.
EXISTING RECOMMENDATIONS AND GUIDANCE REGARDING RESPIRATOR OR MEDICAL MASK USE
Several public health agencies have issued guidance and recommendations for respiratory protection in the event of an influenza pandemic, primarily the Centers for Disease Control and Prevention (CDC) in the United States and the World Health Organization (WHO). Various agencies have also issued guidance specific to the use of respiratory protection to control the transmission of Severe Acute Respiratory Syndrome (SARS) and tuberculosis.
In 2005, CDC issued recommendations for the appropriate use of medical masks as part of a group of influenza control strategies in healthcare settings (CDC, 2005b). Although CDC notes that masks are not usually recommended in non-healthcare settings, its guidance discusses other strategies for limiting the spread of influenza in the community. OSHA’s Guidance for Medical Workers That Transport/Treat Avian Flu Patients states that all patients in a healthcare setting with fever and respiratory symptoms should be managed according to the CDC recommendations (OSHA, 2006).
In healthcare settings during periods of increased respiratory infection activity in the community, CDC recommends that patients with symptoms of respiratory illness be offered medical masks as part of a respiratory
hygiene strategy. The agency recommends that medical masks be worn by patients until
it is established that the symptoms are not caused by a disease which requires precautions against droplet transmission, or
the symptomatic individual has been isolated or placed in a room with other patients with the same infection.
In addition, CDC recommends that as part of standard droplet precautions, medical personnel should wear masks when in close contact with patients who have symptoms of a respiratory infection until or unless the patient is determined to be noninfectious.
Infected adults can spread the influenza virus up to one day before symptoms appear and continue to do so for as long as five days after becoming ill. CDC notes that selective use of masks in non-healthcare settings may not be enough to substantially curtail transmission in the community. Instead, the agency promotes the practice of cough etiquette by persons with respiratory symptoms whenever they are in the presence of another person. The agency encourages sick individuals to avoid contact with others and, if they cannot, to wear a mask.
The CDC Guideline for Isolation Precautions in Hospitals recommends that healthcare workers protect themselves from any disease spread through the air (airborne transmission) by wearing a respirator that is at least as protective as a fit-tested N95 respirator (CDC, 2005a). These guidelines were written before the 2002–2003 SARS epidemic, and they have been used to protect against airborne diseases.
Recognizing that no controlled studies have assessed the efficacy of mask use in preventing transmission of influenza virus, WHO guidance states that use of respiratory protective devices should be based on setting and risk (WHO, 2006).1 WHO recommends that healthcare workers wear masks whenever there is a possibility of splashing or splattering of blood or other body substances, or where airborne infection may occur. In addition, with regard to SARS, particulate filter personal respiratory protection devices capable of filtering 0.3 µm particles with at least 95 percent efficiency
(N95) should be worn at all times when attending patients with suspected or confirmed SARS. WHO’s Interim Infection Control Guidelines for Health Care Facilities states, “If a particulate respirator is not available, a tightly fitting surgical or procedure mask should be used” (WHO, 2006).
Guidance and Regulations on Reuse of Disposable Devices
Most agencies and medical groups recommend one-time use and disposal of medical masks and filtering facepiece respirators or, at the least, that a wearer change the device when it becomes moist. Generally, medical masks should be changed between uses and whenever they become moist.
The Association of Perioperative Registered Nurses recommends that surgical masks not be reused throughout the day or saved by hanging them around the neck or tucking them into a pocket for future use because the filter portion of the mask harbors bacteria collected from the nasopharyngeal airway, and care must be taken when removing the mask to avoid contamination of the hands (AORN, 2005).
The Food and Drug Administration (FDA) defines three kinds of reuse: (1) between patients with adequate processing (as with an endoscope), (2) reuse by the same person with adequate processing and decontamination (as with contact lenses), and (3) repeated use by the same person over a period of time with or without reprocessing.
FDA also divides devices into separate classes. Class I devices are for use in low-risk situations and are mostly exempt from FDA regulation. Class II devices are for an intermediate level of risk; these devices require special and general control. Class III devices are high-risk devices and require premarket approval. Within the FDA framework, masks and respirators are Class II devices.
FDA and WHO recommend disposal of FDA-approved medical masks after one use by one patient (WHO, 2005; FDA, 2006) and that healthcare workers don a new medical mask or respirator each time they come into contact with a new patient (Lin, 2006). The agency states that washing disposable medical masks will destroy their barrier properties so that they will no longer prevent infection; thus, there is no way to disinfect disposable medical masks.
For a device to be approved for reuse, it must meet the following FDA requirements (FDA, 1996):
The instructions must indicate the appropriate microbiocidal endpoint for the recommended reprocessing method.
The reprocessing method must be feasible considering the intended location of reprocessing (e.g., hospital versus home use).
Reprocessing instructions must be validated.
The device must still meet the established performance specifications of the original device after n number of times of repeated reprocessing.
In addition, the design of reusable devices that require cleaning, disinfection, or sterilization between uses must enable the necessary steps to be performed adequately, and manufacturers must establish that devices can be reprocessed effectively after repeated use and must establish and validate procedures for reprocessing.
Manufacturers told the committee that currently marketed disposable medical masks are made of materials that are likely to deteriorate with standard levels of disinfection (e.g., chemicals, heat, radiation). Because medical masks are intended for disposal, and are submitted to FDA with that labeling, manufacturers have no reason or incentive to develop methods for decontamination. However, they noted that it is physically possible for a device to be used repeatedly by the same wearer until it becomes damaged, interferes with breathing, or is visibly soiled (Jensen, 2006; D. Parks, letter to the Institute of Medicine, February 27, 2006). In addition, manufacturers expressed concern that they would incur increased liability if devices designed and intended for disposal were recommended for reuse.
In the context of SARS, the National Institute for Occupational Safety and Health (NIOSH) recommends that workers wear any NIOSH-approved particulate respirator for protection if it has been properly fit-tested and maintained. The agency warns that once worn in the presence of a SARS patient, the respirator should be considered potentially contaminated with infectious material and touching the outside of the device should be avoided. Upon leaving the patient’s room, the disposable respirator should be removed and discarded, followed by hand hygiene.
If a sufficient supply of respirators is not available, NIOSH and CDC recommend that healthcare facilities may consider reuse as long as the device has not been obviously soiled or damaged (e.g., creased or torn). Reuse may increase the potential for contamination; however, this risk must be balanced against the need to provide full respiratory protection to healthcare personnel. The agency recommends that if disposable N95 respirators are
reused for contact with SARS patients, institutions should implement a procedure for safer reuse to prevent contamination through contact with infectious droplets on the outside of the respirator (see Box 3-1). Data on reuse of respirators for SARS are not available.
Also in the context of SARS, WHO recommends that disposable equipment should be used wherever possible in the treatment and care of patients with SARS (WHO, 2003). When the situation dictates the use of nondisposable equipment, the equipment should be sterilized in accordance with the manufacturer’s instructions. Surfaces should be cleaned with broad-spectrum (bactericidal, fungicidal, and virucidal) disinfectants of proven efficacy.
With regard to decontaminating reusable equipment exposed to avian influenza, WHO’s Interim Infection Control Guidelines for Health Care Facilities states: “Avian Influenza is inactivated by a range of disinfectants including sodium hypochlorite (household bleach)” (WHO, 2006).
CONTAMINATION AND REUSE OF MEDICAL MASKS AND RESPIRATORS
Respiratory protection programs must address the issue of respirator contamination either by the wearer or by the environment. This issue is central to considerations of reuse of respiratory protection devices.
Contamination by the Wearer
In the case of negative-pressure respirators (both elastomeric and N95 filtering facepiece respirators; see Chapter 2), in particular, high humidity and temperature inside the respirator can be conducive to microbiological growth (Pasanen et al., 1993; Pasanen et al., 1994; Johnson et al., 1998). This issue has generally been resolved through administrative policies for cleaning and sanitizing. Specific policies depend on whether respirators are assigned to specific individuals or are shared between users. Respirators should not be reused repeatedly without cleaning, and when respirators are used by several individuals they must be cleaned and disinfected before each reassignment (OSHA, 1998).
Generally, filtering facepiece respirators have been considered disposable becqause of the inability to clean and disinfect them (NPPTL, 2006), although some workplaces have allowed repeated wearing of the same filtering facepiece during a single workday (Colton, 2006). In general, these
CDC’s Interim Domestic Guidance on the Use of Respirators to Prevent Transmission of SARS
May 3, 2005
This interim guidance provides information on the selection and handling of respirators for SARS and includes guidance for when respirators are either not available or in short supply.
If N95 respirators are reused for contact with SARS patients, implement a procedure for safer reuse to prevent contamination through contact with infectious droplets on the outside of the respirator.
respirators are not considered “cleanable,” although reuse procedures were implemented to address shortages during the SARS outbreak (see Box 3-1). As previously discussed, medical masks are also considered single-use devices and are generally discarded after a single patient care task or medical procedure.
Contamination from the Environment
Exposure to airborne substances can result in contamination of the external surface of the respirator or medical mask as well as contamination of the filter material. External contamination may result from deposition of
toxic substances (chemical or biological) on the body of the respirator or surgical mask. In an industrial setting, for example, this can occur when the respirator is worn in a dusty environment. An example of contamination in a medical setting is the spread of infectious particles in the vicinity of an infected patient who is coughing or sneezing. This type of contamination is of particular concern when the substance or organisms can enter the body following handling (e.g., via skin absorption, ingestion, or mucous membrane contact). To date, however, the committee was unable to find information on real-world levels of external viral contamination on respirators.
Filter contamination refers, in particular, to the collection of organisms on filters (in the case of aerosol exposures). Laboratory loading tests of inert bacterial particles have found that while filters will capture particles throughout the extent of the media, particles are held with considerable attractive force and are quite difficult to remove, even when the filter is subjected to high bursts of air similar to coughs and sneezes or when dropped onto a hard surface (Qian et al., 1997a; Qian et al., 1997b; Kennedy and Hinds, 2004). As a result, the filter material in respirators and medical masks does not present a hazard during use.
It is possible, however, that heavily loaded filters could release particles during handling because the particles may be held by weaker attractive forces. Although the committee could find no data to indicate what level of loading would be considered “heavy” or at what point particle release might become significant, there is anecdotal evidence that some researchers have been able to culture organisms from gloves after handling loaded filters (L.M. Brosseau, personal communication, March 8, 2006).
RESPIRATOR AND MEDICAL MASK USE IN COMBATING SARS
In 2003, SARS broke out in Canada and Vietnam as well as in Hong Kong, Beijing, and other parts of China. In Toronto, strict infection control measures were implemented for hospital staff that included the use of respirators or medical masks, face shields, goggles, gloves, and gowns. Parents in a pediatric hospital were required to wear a medical mask in most areas that presented a risk of exposure. The Hong Kong government spearheaded a public education campaign on personal hygienic measures with concerted efforts from various organizations and the community (Lo et al., 2005), and as a result 76 percent of the public wore a mask and practiced other personal hygiene measures. A significant drop in the rate of influenza
infection was observed during this period of time. A study with 43 nurses in Toronto who worked with SARS patients showed that both surgical masks and N95 respirators were protective, although consistent use of N95 appeared to reduce the risk more than surgical masks (Loeb et al., 2004).
SARS in Hong Kong, Beijing, and the United States
A case-control study conducted in Hong Kong (Seto et al., 2003) on 241 noninfected and 13 infected staff exposed to SARS patients revealed that mask use alone or in combination with the use of gowns and hand washing was significantly effective in reducing both exposure to and risk of SARS in healthcare workers. Respiratory devices evaluated in this study included paper and surgical masks and N95 filtering facepiece respirators; however, respirators were used only in isolation rooms or during high-risk procedures. Lau et al. (2004a) also reported that frequent mask use in public venues, together with frequent hand washing and disinfecting the living quarters, was a significant protective factor (odds ratio 0.36 to 0.58) against SARS infection. In another report (Lau et al., 2004b), around 40 percent of travelers reported using masks all or most of the time in public places in China or washing their hands frequently. An individual’s perceived susceptibility and understanding of the efficacy of the respiratory protection predicted his or her likelihood of wearing a mask in public places.
A study of the Beijing SARS outbreak showed use of multiple respiratory protection approaches, including gauze masks, nonwoven masks, cotton masks, activated carbon fiber masks, and N95 filtering facepiece respirators. Epidemiological investigators generally used one respirator covered with a surgical mask for each task. Gauze masks with fewer than 12 layers were banned from use. At “fever clinics” and contaminated areas in hospitals or other sites where SARS patient were located, healthcare workers used N95 or FFP22 respirators for an average of two hours. SARS epidemiological investigators were required to discard masks and respirators after leaving contaminated areas and don new surgical masks for the clean area in the hospital. Used respirators and surgical masks were destroyed by incineration as medical waste (Jiang, 2006).
In contrast, the public was encouraged to wear reusable gauze or cotton masks that could be washed with disinfectants or sterilized with high pressure and temperature. Use of masks by the public in addition to social distancing and education on hand hygiene was found to be strongly protective and significantly reduced the risk for SARS (Wu et al., 2004), although the methodological limitations of the study preclude drawing firm conclusions (WHO Writing Group, 2006).
In the United States, Park et al. (2004) conducted a retrospective cohort study and evaluated personal protective equipment use in 66 healthcare workers exposed to SARS patients. They found that 40 percent of healthcare workers did not use a respirator, but none developed SARS, although the sample size was small and the risk of exposure low.
Type of Respirators/Masks Used and Their Efficiency
Jiang (2006) told the committee that there were several types of respirators and masks available in Beijing at the time of the SARS outbreak. These included 8- to 16-layer fabric masks (efficiency 20 percent to 60 percent), nonwoven masks (10 percent to 30 percent), chemical cartridge respirators (55 percent), 2001-8 Xing respirators (59.5 percent), high-efficiency particle respirators (80 percent to 82 percent), fine particle respirators (96 percent to 98 percent), U.S. N95 (96 percent) and French medical respirators (97 percent).3 According to Jiang, the filtration efficiency of respirators/masks used by healthcare workers was less than 17percent for 12-layer fabric masks and charcoal respirators, 46 percent to 48 percent for disposable nonwoven masks, and 95 percent for N95 respirators. Resistance to synthetic blood was good for nonwoven masks without pressure, but not for 12-layer fabric masks. Medical N95 respirators were resistant to blood penetration, but the industrial N95 respirators were not. As to resistance to microbial breakthrough, medical and industrial N95 respirators and nonwoven masks were both effective, but the 12-layer fabric masks were not (Jiang, 2006).
Concerns have been raised regarding the availability and cost of N95 filtering facepiece respirators to be used by the public during an outbreak,
and some persons have questioned whether medical masks might be used as a substitute. Weber and colleagues (1993) tested eight different surgical masks and found that filter penetration ranged from 20 percent to 100 percent for submicrometer-sized particles. Later, following the SARS outbreak, Derrick and Gomersall tested the fit factor of multiple surgical masks, defined as the average ratio of atmospheric to in-mask particle concentrations. Their testing showed that the best combination of five surgical masks provided a fit factor of 13.7, dramatically less than the OSHA-required fit factor of 100 for N95 half-mask respirators.
Citizens in India routinely wear woven cloth masks as well as disposable nonwoven masks in the hope of protecting themselves from infection. In the course of its deliberations, a member of the committee interviewed some public health nurses in India to assess the relative use and effectiveness of woven cloth masks versus disposable nonwoven masks. Woven (cotton) cloth masks continue to be widely used in government hospitals because they have a useful life of several years and are easy to carry, nonallergenic, comfortable, affordable, and washable. They do not offer the same level of protection as disposable nonwoven masks and are not recommended for operating room use in the United States because of their lack of tested fluid resistance (AORN, 2005). However, some public health workers in India find them to be a cost-effective measure for lower risk environments, particularly if the fit of the woven cloth mask can be improved. Their efficacy against influenza is undetermined at this point.
SUMMARY AND CONCLUSIONS
Any estimate of N95 filtering facepiece respirator or medical mask effectiveness in limiting the spread of an influenza outbreak should be based on influenza-specific clinical data. However, little information on this topic is available in the literature. Data emerging from the SARS experience may deserve more careful consideration. Thus, choosing an appropriate estimate of the effectiveness of respiratory protection is a significant challenge.
Nonetheless, it is widely acknowledged that disposable N95 respirators can be effective devices in filtering out hazardous and pathogenic contaminants. The data on medical masks are far less conclusive. Fit will have a great impact on effectiveness in the event of an outbreak, and methods of use, including location of use, are likely to be significant factors as well.
Disposable medical masks and respirators were not designed for reuse, and there is nearly universal agreement that reuse, even by a single user,
should be discouraged except in the most extreme and dire circumstances. The next chapter provides the committee’s findings and recommendations about reuse, and the circumstances under which it might be considered.
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