Introduction and Background
The threat of an avian influenza1 pandemic has been widely reported in popular media, government publications, and scientific journals. Planning for pandemic influenza presents clear and unique challenges because it is difficult to know when the next pandemic will arise. The potential duration and severity are also impossible to predict. Moreover, the duration of an influenza pandemic could be weeks or months, with several epidemic waves that could deplete the energy and resources of healthcare facilities and providers. Because influenza viruses are mutable and adaptable, new vaccines must be developed on a continual basis to keep up with constantly changing viral strains. Primary prevention strategies, including vaccines and antiviral prophylaxes, are likely to be either unavailable, depending on the influenza strain, or initially limited in quantity and availability.2
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 the virus in both the healthcare and community sectors. Such measures can be deployed at the community level, for example, by closing schools and other public places. In addition, these measures can be implemented at the individual level by isolating patients, limiting contacts with infected persons, and otherwise minimizing the likelihood of exposure to the virus. These steps can be voluntary, such as respiratory hygiene/cough etiquette and frequent hand washing, or mandatory, such as by requiring infected individuals to be quarantined or equipped with medical masks that might limit respiratory transmission of the virus.
Clearly there is widespread public interest and concern about pandemic influenza, its transmission, the probability that it will occur, and what can be done to protect the public’s health. Public health officials and organizations throughout the world remain on high alert because of increasing concerns about the prospect of an influenza pandemic, which many experts believe to be inevitable. Most of the current fear of a potential pandemic stems from an outbreak of avian influenza in Asia, Africa, and Europe; infected birds are known to be in 45 countries at the time of this writing (CIDRAP, 2006). Hundreds of millions of wild and domesticated fowl have died from this virus, either through illness or culling. According to the U.S. Department of Homeland Security (DHS), despite the use of traditional control measures, the avian virus is “now endemic in Southeast Asia, present in long-range migratory birds, and unlikely to be eradicated soon” (DHHS, 2006). At this point, the reported number of humans infected remains low in comparison to the number of birds infected—192 confirmed cases in 9 countries over the past 4 years. Of those cases there have been 109 reported deaths (WHO, 2006). The committee found no estimates of the number of cases not reported. As the reported cases stem from those seeking medical care, the death rate may be artificially high.
The H5N1 virus can infect a variety of hosts, including birds and humans, but has not yet demonstrated the ability to be transmitted efficiently among humans. However, via genetic mutation or exchange of genetic material with a human influenza virus, it may develop this capability. Such a change may lead to devastating consequences. And, if mutation and human-to-human transmission do not ensue with the current H5N1 strain, there is a great likelihood that another strain will lead to a pandemic. During the 20th century, there were three pandemics that arose as a result of
new influenza virus subtypes: the 1918–1919 “Spanish flu” caused more than 500,000 deaths; the 1957–1958 “Asian flu” resulted in 70,000 deaths; and the 1968–1969 “Hong Kong flu” killed about 34,000 people (DHHS, 2005a).3
Pandemic influenza differs from seasonal influenza. Seasonal influenza outbreaks result from minor mutations in viruses already circulating in a given community; thus, most individuals have some degree of immunity to seasonal influenza, and the health effects tend to be less severe. Seasonal influenza’s greatest impact is among the very young, the elderly, those who are immunocompromised, and those with lung disorders or other chronic illnesses. According to the CDC, annual (seasonal) influenza outbreaks result in around 36,000 deaths and greater than 200,000 hospitalizations each year in the United States (CDC, 2005b).
In contrast, an influenza pandemic generally occurs with the emergence of a novel strain of the influenza A virus that can infect humans and is easily transmitted from person to person. By definition, a pandemic is global in nature (DHHS, 2005a) and may be particularly devastating because human populations will have little, if any, baseline immunity to an entirely new viral strain.
Appropriate planning for protection against a major influenza pandemic requires an understanding of the mechanisms of influenza transmission. More important, developing and implementing the most effective interventions (e.g., vaccination, respiratory protection, and/or quarantine) requires detailed knowledge about the relative role played by the various modes of transmission. The committee’s review of scientific literature found vigorous debate about the mechanisms of influenza transmission and a lack of clear evidence supporting a single mode (Garner and The Hospital Infection Control Practices Advisory Committee, 1996; Goldmann, 2000;
Salgado et al., 2002; Stott et al., 2002; Bridges et al., 2003; CDC, 2005b). In addition, little is published about the infectious dose of this virus. Most experts agree, however, that pandemic influenza will be spread in the same way as seasonal influenza (Bridges et al., 2003; Yuen and Wong, 2005; DHHS, 2005b; Wong and Yuen, 2006).
CDC’s Hospital Infection Control Practices Advisory Committee describes three modes of transmission believed to be relevant to the spread of influenza: (1) droplet, (2) contact, and (3) aerosol. The relative importance of each mode of transmission is unknown.
Droplet transmission comes from conjunctival or mucous membrane contact with large-particle droplets (typically larger than 5 µm) that contain microorganisms from an infected person. Droplets of varying sizes may be propelled short distances (usually less than 3 feet) from an infected individual to a susceptible host by coughing, sneezing, or talking (DHHS, 2005b). Some studies suggest that influenza is spread mainly through this mode of transmission, with the smaller particles being the most efficient in infecting individuals (Salgado et al., 2002). Thus, respiratory hygiene/cough etiquette with disposable tissues is an essential feature of limiting transmission of influenza, as is frequent hand washing by both infected and exposed persons. As large droplets do not remain suspended in the air for an extended period of time, air-handling and ventilation systems will not assist in controlling droplet spread (DHHS, 2005b).
Contact transmission of influenza through either direct skin-to-skin contact or indirect contact (contact with contaminated objects, such as hands or countertops) has been suggested as a factor contributing to transmission in some studies (Bean et al., 1982). Thus, hand hygiene, that is, frequent hand washing, using soap and water or alcohol-based hand gels, is an essential feature of limiting influenza transmission through contact (WHO Writing Group, 2006).
Aerosol transmission involves the dissemination of either airborne droplet nuclei or minute infectious particles. These can include respirable particles (mass median aerodynamic diameter smaller than 5 µm), thoracic particles (mass median aerodynamic diameter smaller than 10 µm), and inspirable particles (mass median aerodynamic diameter smaller than 100 µm). Evidence for airborne transmission of influenza is limited, but studies in animals and humans have raised significant concerns that airborne transmission is a potentially important mode of transmission for some infectious agents (Alford et al., 1966). It is probable that “aerosol-generating procedures (e.g., endotracheal intubation, suctioning, nebulizer treatment,
and bronchoscopy) could increase the potential for dissemination of droplet nuclei” (DHHS, 2005b). This probability makes consideration of aerosol protection an important part of infection control planning.4
RESPIRATOR OR MEDICAL MASK USE AS A NONPHARMACOLOGICAL INTERVENTION
In the event of pandemic influenza, supplies of effective vaccines and antiviral medications are likely to be inadequate to treat a very large number of affected individuals. Therefore, nonpharmacological interventions will be important, including the use of respiratory protection through respirators or medical masks or both (see Box 1-1 for definitions). WHO recommends nonpharmacological interventions that focus on delaying the spread of infection and reducing the impact of the disease (WHO Writing Group, 2006). WHO’s recommendations include permitted, but not required, routine mask use by the general public.
Currently, medical masks are recommended by CDC for use in healthcare settings for routine patient care.5 In addition, National Institute for Occupational Safety and Health (NIOSH)–certified N95 respirators (in contrast to medical masks) are recommended for use in high-risk activities (e.g., aerosol-generating procedures) in healthcare settings and have been recommended for use in controlling the spread of other infectious agents, including, but not limited to, Severe Acute Respiratory Syndrome (SARS) and tuberculosis (CDC, 2005a).6 However, currently available medical masks and disposable N95 filtering facepiece respirators have a limited effective life span. Once worn, they can become damaged or deformed or develop intolerable levels of breathing resistance from moisture buildup. If worn in an environment with high probability of exposure to infectious agents (e.g., healthcare facilities and/or closed spaces), they can become contaminated.
Definitions of Key Terms Used in This Report
Respirator: A NIOSH-approved device that when properly fitted, protects the wearer against inhalation of harmful atmospheric contamination. In the context of this report, unless otherwise specified, the term “respirator” refers to an N95 filtering facepiece respirator. Properly fitted respirators provide better protection against airborne transmission of infectious particles than do medical masks.
N95 Filtering Facepiece Respirator: A disposable respirator with a filtering facepiece that has been tested and certified by NIOSH and meets the NIOSH criteria for a minimum 95 percent filter efficiency at the most penetrating particle size. Not to be used in an environment with an oily atmosphere.
Medical Mask: An unfitted device designed to reduce exposure to or transmission 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, but they are not designed to fully protect the wearer from entry of infectious particles via leakage around or through the mask. There are two types of medical masks: surgical and procedure masks.
Reuse: Repeated use of a respirator or medical mask. This can be use over an extended period of time or use following cleaning and disinfection.
Medical Mask/N95 Filtering Facepiece Respirator: A NIOSH-approved N95 respirator that also meets FDA’s fluid resistance requirements.
Given the potential duration of a pandemic, even stepped-up production and stockpiling of disposable medical masks and N95 respirators may not be sufficient to meet demand, especially if community use of either device is widespread. CDC estimates that in the event of a severe influenza pandemic, at least 1.5 billion medical masks would be needed by the healthcare sector and an additional 1.1 billion would be needed by the public. Demand for N95 respirators by the healthcare sector could exceed 90 million for a 42-day outbreak (CDC, 2006).
CHARGE TO THE COMMITTEE
On the basis of the assumption that efforts to produce and stockpile sufficient supplies of disposable medical masks or respirators or both may fall short in the event of a pandemic, in January 2006 DHHS asked the Institute of Medicine (IOM) to convene a committee to conduct a 90-day assessment of
measures that can be taken that would permit the reuse of disposable N95 respirators in healthcare settings and
the need for, and development of, reusable face masks for healthcare providers and the public.
Specifically, the committee was asked to address two major sets of issues, as described in Box 1-2.
The IOM Committee on the Development of Reusable Facemasks for Use During an Influenza Pandemic consists of members with expertise in the areas of epidemiology, risk assessment, public health, infectious disease, emergency and respiratory medicine, industrial hygiene, personal protective equipment (including respirators), occupational safety and health, textile engineering, polymer science and engineering, pathobiology, and anthropometrics. The committee met twice, in January and March 2006, to convene public workshops and develop this report (see Appendix A).
This report is an analysis of the potential for respirator and medical mask reuse. It also discusses the potential of unconventional protection, such as by woven cotton masks and improvised protection, and proposes an agenda for research. This report does not propose standards for respiratory protection, nor should it be seen as in conflict with existing standards. The committee was asked to consider worst-case scenarios; it is the committee’s expectation that protection offered in all situations will be in
Charge to the Committee
The first issue to be addressed in the report concerns measures that can be taken that would permit the reuse of disposable N95 respirators in healthcare settings. Examples of the types of questions that will be considered include: what modifications can easily be made in the manufacturing process that would permit these respirators to be reused without increasing the likelihood of infection with the flu virus; and what practices in caring for, wearing, and cleaning could be implemented to safely extend the effective lifetime of disposable N95 respirators? The number of available respirators is only one limiting factor in the context of a pandemic. Fit-testing of N95 respirators may not be practical for healthcare facilities to sustain on a large scale during a pandemic when very large proportions of staff might need to wear respirators. If a simple adjustment or modification in the manufacturing process could obviate that need, such a recommendation would also be highly useful to DHHS.
The second issue to be addressed in the report concerns the need for reusable masks for healthcare providers and the general public. In the event of an extended pandemic, there will be the inevitable increasing demand by the public for masks, which cannot be met by the current, or even ramped-up U.S. production of disposable masks. Examples of the types of questions related to design of reusable masks that will be considered include: what materials would be effective; what would be an acceptable level of fluid resistance and filtration efficiency (e.g., individual to prevent respiratory droplets from being dispersed, and to reduce exposure to potentially infectious material, that is, to ensure that reusable masks for noninfected individualsfilter inflowing airto minimize exposure to the flu virus, and reusablemasks for
compliance with existing standards and legal requirements, but the committee acknowledges that there may be difficulty in meeting such standards during a pandemic situation.
Because the committee consisted of members drawn from a diverse range of backgrounds and perspectives across medical science, engineering, and public policy, it was necessary to develop a common vocabulary (see the Glossary, Appendix C) and also an understanding of the assumptions
infected individuals minimize the chances that these individuals willinfect others); and what characteristics would be optimal for such variables as wearability and ease of removal, durability, ease and effectiveness of washing, and cost-effectiveness for widespread public use.
Additional issues the committee may consider in the context of the above questions include:
Identification of research questions for short- and long-term study regarding respiratory protection against infectious diseases.
that must be made when developing a strategy to control the spread of a pandemic with unknown and uncertain dimensions through respiratory protection.
Following this introductory chapter, Chapter 2 outlines the differences between respirators and disposable medical masks and explores the materials and components used in their production. In addition, Chapter 2 describes the processes needed for regulatory approval of respirators and
masks. Chapter 3 describes what is known about the use of respirators and medical masks to control the spread of infectious disease, including the potential for extended use or reuse after cleaning and disinfection of disposable respirators and medical masks, how they become contaminated, what is known about how to decontaminate them, risks of reuse, and current regulations governing reuse. Chapter 4 presents the committee’s findings and recommendations and suggests areas for future research.
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