Respiratory Protection: Compliance, Research are Key Issues for the Future

By Kelly M. Pyrek

Ensuring healthcare worker compliance with the proper use of respiratory protection when it is warranted remains a challenge for infection preventionists and is a continued area of study by researchers in the public and private sectors. One such agency pursuing this knowledge is the National Institute for Occupational Safety and Health (NIOSH), the federal agency specifically dedicated to generating new knowledge in the field of occupational safety and health and to transferring that knowledge into practice.

The National Personal Protective Technology Laboratory (NPPTL) is the NIOSH division that is responsible for generating scientific research and developing guidance that can help to better inform the agenda that prevents disease, injury and death for U.S. workers relying on personal protective equipment (PPE). The NPPTL, established in 2001 at the request of Congress, was created in response to a recognized need for improved PPE and focused research into personal protective technologies (PPT).

Respiratory protection is the cornerstone of NPPTLs efforts, and in 2008, as a recommendation from the National Academies, it was advised that increased research on the use and usability of PPE be conducted. At the same time, it was recommended that the NPPTL continue its research in priority areas such as new-materials technology (including no-fit test respirators); comfort, ergonomics, and human factors which determine whether or not the PPE is worn by the worker; and enhancing the culture of workplace safety through worker education, training and understanding of hazardous exposure risk to health.

 
Debra Novak, DSN, RN, a senior service fellow with NIOSH and the NPPTL, explains that a renewed focus on PPE and respiratory protection specifically was triggered by what she calls a "symphony of events" that included not only the IOM reports but the H1N1 influenza pandemic in 2009.

 
"These events synergistically came together to a point where we at the NPPTL started to recognize that there seemed to be a compliance problem with proper usage of respiratory protection," Novak explains. "Out of that came a series of funded studies that we were able to initiate, with the first being the Respiratory Evaluation for Acute Care Hospitals (REACH) study, or REACH I, which started in California. We then expanded to a REACH II study that looked at respiratory protection usage in five regions in the U.S.

In the REACH I study, the goal was to assess the usage of respiratory protection for influenza exposure among healthcare workers in 16 participating healthcare organizations. Onsite surveys and observational data collection methods were employed in each facility and 204 healthcare workers participated in the study from a variety of clinical specialties. Several trends emerged, including respirator re-donning.  In answer to the survey question, "Have you ever re-used an N95 respirator when in close contact with patients who have confirmed or suspected H1N1?" 57.7 percent of participating healthcare workers said "no," while 42.3 percent said "yes." If the answer was "yes," healthcare workers indicated they reused a respirator because of a shortage or respirators, or that it was standard practice, or they simply didn't know why they reused a respirator.

Common problems with N95 respirators as cited by the healthcare workers surveyed included:  uncomfortably warm (39 percent); interferes with other PPE (21 percent); difficulty in speaking or being understood (20 percent); difficulty breathing (16 percent); moisture build-up (13 percent); claustrophobic (10 percent); other (8 percent) and interferes with glasses (4 percent). Thirty-five percent of the surveyed healthcare workers reported no problems.

In answer to the question, "How do you know that you need to wear a respirator?" Healthcare workers reported that there was a sign on the door of the patient's room (194); they were told during a shift report (165); they conducted a patient assessment that indicated respirator use (156); co-workers informed them (155); respirators were located near a patient's room (118); a supervisor informed them (68); or another method was used (35).

In terms of what healthcare workers believe about PPE usage, 65 percent of surveyed healthcare workers said they thought they were at high risk of becoming ill with influenza due to their work (35 percent disagreed); 96 percent said that wearing an N95 or better respirator can help protect them from exposure to influenza (3 percent disagreed); and 94 percent said respirators are more effective at protecting them from influenza than surgical masks (3 percent disagreed and 2 percent weren't sure).

Other findings from the REACH I study included:
- 50 percent of the hospital managers reported that their facility had experienced a shortage of respirators between April 2009 and the survey period (Jan. 20-Feb. 23, 2010).
- The observational data indicates improper use of respiratory protective equipment as evidenced by donning and doffing practices, including not performing a seal check, improper strap placement and touching the facepiece upon doffing.

The REACH I study found that the most deficient areas of the written program were designation of a respirator program administrator; recordkeeping; fit-testing protocol; training; and program evaluation. Areas of implementation with the greatest need for improvement included selection of appropriate respirator for task and suspected/confirmed infectious disease risk; donning/doffing N95 respirators; regular evaluation of program; and employee use of the specific respirator for which they were fit-tested.

In March of this year, NIOSH and the NPPTL held a personal protective technologies stakeholder meeting during which participants received an overview of recent efforts to identify innovative, effective strategies and practices to strengthen healthcare respiratory protection programs, and to identify challenges associated with the implementation of these programs. The meeting also included an update on the REACH II study; while the results are still being processed, preliminary findings indicate that:
- Respiratory protection program plans exist on paper
- Response differences between HCWs and hospital managers regarding operations of the respiratory protection program.
- Most healthcare workers recall fit-test at hire with minimal updates.
- Fit-testing is the focus, while ongoing preparedness training is not
- Respirators (N95s) are most commonly used for TB.
- Healthcare workers are infrequent N95 respirator users
- Healthcare workers are improperly donning and doffing respirators

Novak observes, "Over time and through these studies we began to see that workers were not using respiratory protection either at all or using it correctly." This comes as little surprise to Novak, who points to the scientific literature demonstrating marginal compliance with the proper use of respiratory protection. "Redonovich (2008) put the compliance factor at less than 60 percent, but even scarier is what OSHA is telling us in terms of illness and injury in healthcare facilities," Novak says. "I was alarmed to see the recent OSHA statistics that in 2010 healthcare organizations were No. 1 in terms of illness and injury. Clinical events like H1N1, then illness and injury rates from OSHA, and the fact that so many safety climates are woefully inadequate -- combine those factors together, which makes the proper use of respiratory protection an issue we need to pay attention to."

To help healthcare organizations prevent worker and patient exposures to hazardous agents, NIOSH and the NPPTL are using the results of these REACH studies to develop an educational monograph containing effective practices, tools and resources to help hospitals improve their respiratory protection programs. The monograph is a welcome tool, seeing that healthcare facilities now must find much of their instruction in the OSHA standard itself.

OSHA's respiratory protection standard, 29 CFR 1910.134, declares, "In the control of those occupational diseases caused by breathing air contaminated with harmful dusts, fogs, fumes, mists, gases, smokes, sprays, or vapors, the primary objective shall be to prevent atmospheric contamination. This shall be accomplished as far as feasible by accepted engineering control measures (for example, enclosure or confinement of the operation, general and local ventilation, and substitution of less toxic materials). When effective engineering controls are not feasible, or while they are being instituted, appropriate respirators shall be used pursuant to this section." [1910.134(a)(1)]. It also states, "A respirator shall be provided to each employee when such equipment is necessary to protect the health of such employee. The employer shall provide the respirators which are applicable and suitable for the purpose intended. The employer shall be responsible for the establishment and maintenance of a respiratory protection program, which shall include the requirements outlined in paragraph (c) of this section. The program shall cover each employee required by this section to use a respirator." [1910.134(a)(2)]
The respiratory standard establishes the requirement that in places of employment where respirators are used -- such as in healthcare facilities -- a written respiratory protection program with worksite-specific procedures must be created and maintained.

The employer must include in the program the following:
- Procedures for selecting respirators for use in the workplace
- Medical evaluations of employees required to use respirators
- Fit testing procedures for tight-fitting respirators
- Procedures for proper use of respirators in routine and reasonably foreseeable emergency situations
- 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
- Training of employees in the respiratory hazards to which they are potentially exposed during routine and emergency situations
- Training of employees in the proper use of respirators, including putting on and removing them, any limitations on their use, and their maintenance
- Procedures for regularly evaluating the effectiveness of the program

In addition, the employer must establish and implement those elements of a written respiratory protection program necessary to ensure that any employee using a respirator voluntarily is medically able to use that respirator, and that the respirator is cleaned, stored, and maintained so that its use does not present a health hazard to the user. The employer must also designate a program administrator who is qualified by appropriate training or experience that is commensurate with the complexity of the program to administer or oversee the respiratory protection program and conduct the required evaluations of program effectiveness. OSHA also expects the employer to provide respirators, training and medical evaluations at no cost to the employee.

Novak says that OSHA's respiratory standard is the main driver for respiratory protection in the healthcare workplace, and says she is concerned that many facilities lack a structured program that ensures compliance.

 
"One of the things we have been advocating for is a working group in which an infection preventionist, the healthy and safety officer, the risk manager, and the respiratory protection administrator are all sitting down at the same table and working it out," Novak says. "But that's a best practice that smaller healthcare facilities may or may not be able to accomplish."

What is also needed, Novak emphasizes, is further evidence of the connection that establishes transmission of an infectious pathogen to an individual not wearing proper respiratory protection. She points to the California Aerosol Transmissible Disease (ATD) standard as one of the strongest pieces of regulation that addresses "exposure from work activity or working conditions that is reasonably anticipated to create an elevated risk of contracting any disease caused by ATPs or ATPs-L if protective measures are not in place." The standard defines aerosol transmissible disease (ATD) or aerosol transmissible pathogen (ATP) as "a disease or pathogen for which droplet or airborne precautions are required," and defines an aerosol transmissible pathogen-laboratory (ATP-L) as "a pathogen for which Biosafety in Microbiological and Biomedical Laboratories (BMBL) recommends biosafety level 3 or above for the pathogen... or the pathogen is a novel or unknown pathogen."  In this context, elevated" means higher than what is considered ordinary for employees having direct contact with the general public outside of the facility addressed by this standard, and occupational exposure is presumed to exist to some extent. The ATD standard makes it clear that NIOSH-approved respirators are required in situations that warrant them, and that every employer who has any employee whose occupational exposure is based on entering a work setting or performing any of the tasks covered by the standard, must establish, implement and maintain an effective written respiratory protection program that meets the ATD standard's requirements.

Novak also points to several benchmark clinical examples. "California's ATD standard is a good start. We do know there was a transmission of a highly virulent strain of bacterial meningitis where the two individuals who got sick did not wear any respiratory protection at all while other individuals who knew to don N95s did not get sick. Another case involved surgical plumes, with transmission of disease to individuals who were exposed when they were cauterizing condylomas.

Condylomas were found growing in the oropharyngeal cavity of OR personnel due to exposure and these healthcare workers not wearing respiratory protection. These are the two clinical benchmarks we can point to, as well as the California ATD standard. These are the evidence-based directions we have currently -- it's not a lot but it's all we have." 

 
Novak continues, "One of the principles I try to advance every time I have a chance is the precautionary principle from epidemiology. In other words, if there is a reasonable suspicion that a risk exists, be it biological, chemical, or due to an exposure, prudent action would defer us to a precautionary approach, which means you use your PPE when you are suspicious, period. Everyone wants cause-and-effect relationships and proof beyond a reasonable doubt, but we can't do that. However, that doesn't give us a free pass either. We have glimpses of what we should know, but we don't have ad advanced compendium of evidence -- we only have an indication there is a reason for concern at this point."

Until such time as a greater body of proof exists, Novak emphasizes that healthcare workers -- and their facilities -- must take respiratory protection seriously.
"We do know it's a commitment to organizational safety that must be made," Novak says. "You must have someone constantly saying to healthcare workers, 'This is important.' As well, the healthcare professional must be an advocate for their own personal safety and they have to be informed -- I don't believe they are as informed as they could be right now. They are also not getting this instruction in school; the amount of infection control instruction they receive in an undergraduate degree is woefully inadequate. We have a healthcare workforce out there right now, for a variety of reasons, that is unprepared for occupational biological exposures. The focus needs to be on the biologicals but if you look at other potential exposures in the healthcare workplace, there is a lot to be worried about."

That sentiment was echoed in a report from the National Occupational Research Agenda (NORA) program, created by NIOSH to stimulate innovative research and improved workplace practices in occupational safety and health. The NORA report (HHS 2009) acknowledges, "In addition to bloodborne pathogens, healthcare workers are also at risk for a number of other occupationally acquired infectious diseases. Depending on the specific pathogen, transmission can occur via direct contact with patients and contaminated surfaces, or airborne bio-aerosols, generated mainly by sneezing and coughing, that range from large projectile droplets to small particles remaining in the air.. The potential threats associated with new and emerging infectious hazards have caused much concern; these threats include SARS, avian influenza, pandemic influenza, and multidrug-resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and extensively drug-resistant tuberculosis (XDR-TB). Since the anthrax attacks of 2001, there has also been great concern about the risks that healthcare workers might face in subsequent attacks using highly contagious bioterrorism agents such as smallpox. In many cases, interventions exist to prevent transmission. Handwashing, vaccination, and rapid recognition and appropriate isolation of potentially contagious patients are especially important interventions. There are a number of opportunities for research with relevance and impact. Although routine surveillance is performed for some infectious diseases, there is no broadly representative, ongoing surveillance for all infectious diseases across the sector. Research is needed to identify barriers to adherence and achieve better implementation of known, effective interventions such as handwashing and immunization for influenza. A particularly important need is to better understand the potential for agents, such as SARS and influenza, to be transmitted via the airborne route. A related need is to better understand how exposures to airborne infectious agents should be reduced using interventions such as engineering controls and personal protective equipment. In the case of personal protective equipment, implementation issues, such as appropriate frequency of fit testing, have been particularly controversial; research could help to resolve this."

The NORA report (HHS 2009)  includes PPE and contact precautions in the top interventions that can help stop the spread of disease: "Rapid recognition of patients with potentially contagious conditions and isolation with appropriate precautions can be challenging, but is a well-established practice. ... Personal protective equipment such as examination gloves, gowns, eye shields, face masks and respirators can also be used to limit exposures. Use of respiratory protection is a well-established intervention preventing transmission of some diseases, such as TB. Respiratory protection is also recommended for preventing transmission of other diseases. For example, when entering the room of a patient with suspected avian influenza or SARS, CDC recommends use a fit-tested respirator, at least as protective as a NIOSH-approved N-95 filtering facepiece respirator. The Department of Health and Human Services (HHS) has also made recommendations for use of respirators in the setting of pandemic influenza. N-95 or more protective respirators are recommended in settings at high risk for aerosol generation, such as intubation, bronchoscopy, nebulizer treatment, resuscitation, and care of patients with pandemic-influenza related pneumonia. Use of N-95 respirators whenever caring for patients with confirmed or suspected pandemic influenza is noted to be 'prudent.' However, HHS notes that 'Development of authoritative responses is hampered by the lack of definitive data about the relative contributions and importance of short-range inhalational exposure, large droplet mucosal exposure, and direct inoculation via hands or inanimate objects contaminated with virus (i.e., fomites) on influenza transmission. There is only limited information on optimal interventions to prevent influenza transmission and the effectiveness of interventions on an individual basis.''

The report (HHS 2009) adds, "In addition to improving implementation of known interventions, basic and applied research is needed in a variety of areas to assess and/or improve the efficacy of potential preventive measures and to improve the evidence base for public health recommendations. Improved methods for rapid detection of infectious agents and assessing their levels might be useful for rapid identification and isolation of infectious patients, as well as assessment of environmental contamination. New technologies, such as nanotechnology-based bio-sensors and chemical sensors, might be useful in methods development. Good measures of exposure to infectious agents would allow investigators to perform epidemiological and other studies to quantify exposure-infection relationships. Understanding these relationships, in turn, could inform recommendations on what levels of disinfection and what type of PPE would be required to protect against transmission of infection. Work is needed to understand whether or to what degree that pathogens typically thought to be transmitted primarily by droplet SARS coronavirus, influenza can be transmitted via the airborne route or via contaminated fomites or surfaces. This knowledge would provide very useful evidence for or against use of various interventions including surface decontamination, environmental controls and PPE."

The NORA report (HHS 2009) calls for research that would "objectively document and/or improve of the ability of respiratory protective devices to reduce exposures to infectious agents and, ideally, to document efficacy in reducing transmission of infection. Such research could address important issues such as assessing and improving respirator fit and facial sealing, assessing and improving particulate filter performance, and assessing and improving respiratory program recommendations including approaches to training and fit testing. Improved understanding of the ability of contaminated respirators to transmit infection and approaches to decontamination of filtering face piece respirators might improve supply under conditions of high demand, such as during epidemic or pandemic influenza outbreaks."

An especially important need, according to the NORA report (HHS 2009), is research addressing the role of PPE in protecting healthcare workers during an influenza pandemic: "Early in an influenza pandemic, appropriate vaccines will be unavailable and healthcare workers will generally lack protective immunity. Under these conditions, use of PPE will be an important part of efforts to protect healthcare workers. In 2006, NIOSH requested the Institute of Medicine (IOM) to conduct a study addressing this area. In its report (IOM 2008), IOM notes that 'There is an urgent need to address the lack of preparedness regarding effective PPE for use in an influenza pandemic. Three critical areas were identified that require expeditious research and policy action: (1) Influenza transmission research should become an immediate and short-term research priority so that effective prevention and control strategies can be developed and refined. The current paucity of knowledge significantly hinders prevention efforts. (2) Employer and employee commitment to worker safety and appropriate use of PPE should be strengthened. Healthcare facilities should establish and promote a culture of safety. (3) An integrated effort is needed to understand the PPE requirements of the worker and to develop and utilize innovative materials and technologies to create the next generation of PPE capable of meeting these needsThe committee believes that improvements can be made so that healthcare workers will have PPE that provides protection against influenza transmission based on a rigorous risk assessment with solid scientific evidence.'" A detailed action plan to address the IOM recommendations has been developed by the NPPTL (NPPTL 2008).

Let's take a look at what the literature says. Mermel (2009) points to the seemingly contradictory findings in the literature when it comes to airborne transmission and implications for the transmission of influenza -- all contingent on predicting the presence of a "superspreader" as well as understanding "superspreading" events: "A lack of airborne transmission was found in a recent cluster of people infected with A H1N1 2009. Importantly, surgical masks worn by nurses caring for patients with influenza-like symptoms were as effective in protecting them from influenza as fit-tested N95 respirators,8 suggesting minimum aerosol transmission. However, in another study, N95 respirators worn by health-care workers for four weeks during winter were highly effective in preventing infection with influenza, and surgical masks afforded no protection. Variability in the quantity of bioaerosols produced by individuals infected with influenza suggests that superspreaders or superspreading events pose a risk of influenza that is the Achilles heel of infection control. Our limited understanding of such superspreading events leaves us vulnerable since we cannot predict which person infected with influenza is a superspreader. To minimize such risks, healthcare workers can wear N95 respirators when caring for patients presenting with influenza-like symptoms, but compliance is problematic, there is incremental cost of N95 respirators compared with surgical masks, limited industrial capacity to meet the demands in the midst of a pandemic, and potential penetration of viral particles through N95 respirators. Immune status of a health-care worker is another important variable. The role of personal protective equipment might be inconsequential if a caregiver has protective immunity to A H1N1 2009."

Mermel (2009) adds, "Science will guide us as we care for patients infected with A H1N1 2009 but a lack of attention to our understanding of the transmission of human influenza has left us debating which procedures create influenza superspreading events, what is appropriate personal protective equipment, use of suboptimum engineered respirators that need fit-testing and are poorly tolerated for prolonged use, and limited industrial capacity to meet our needs. For now, infection control experts at each institution must weigh the variables to establish not only what is best, but what is realistic in reducing risk to their staff, their visitors and their patients."

Many healthcare professionals were exposed to the 2009 H1N1 influenza virus during the first wave of the pandemic because they were not using respiratory protection and/or other pieces of personal protective equipment (PPE). Banach, et al. (2011) suggest that unprotected exposures tended to be more frequent among healthcare workers caring for patients with atypical clinical presentations. The researchers conducted a study in a large teaching hospital in New York City in which a screening protocol was introduced in early April 2009 to identify patients presenting to the emergency department (ED) and other locations with influenza-like illness (ILI). The protocol was designed to rapidly identify cases in order to minimize the risk of influenza transmission by implementing infection prevention precautions (including cough etiquette, physical separation, and use of appropriate PPE) by personnel providing care to the patient. The researchers report that healthcare worker contact investigations were performed for all patients with confirmed 2009 H1N1 infection, and unprotected exposure was defined as providing care within six feet of a patient without using PPE.

The researchers reviewed all unprotected healthcare worker exposures between May 22 and July 6, 2009, and examined infection control records to identify patients admitted from the ED who were confirmed to have 2009 H1N1 infection. Information about the healthcare worker exposures was obtained from contact investigation records. During the study period, 44 ED patients had 2009 H1N1 infection diagnosed and 37 met the definition for presence of ILI. Twenty-six patients were involved in one or more unprotected HCW exposures. A total of 277 unprotected exposures were identified. The researchers report that the location of unprotected healthcare worker exposures included the ED (57 percent), inpatient units (41 percent) and other locations (2 percent). Exposures involved 41 percent of nurses, 32 percent of physicians and 17 percent of ED technicians and patient care assistants on inpatient units.

Banach, et al. (2011) note, "The identification of almost five unprotected healthcare exposures for each patient who presented with ILI was a more unexpected finding. Potential explanations include inconsistent use of the screening and isolation protocol, communication barriers, and suboptimal adherence to recommended PPE use. Each of these warrants further research. Previous studies have demonstrated that healthcare worker compliance with respiratory protection guidance, including that related to influenza, is generally poor. A recent study of healthcare workers opinions about respirator use identified the need for new equipment that better meets the needs of healthcare workers." Banach, et al. (2011) add, "Since substantial numbers of unprotected exposures occurred during this period of heightened awareness of influenza and at a time when vaccination was not an option, it is likely that similar or perhaps even more exposures occur during typical influenza seasons. This highlights the importance of healthcare worker immunization, when available, and the need for a better understanding of barriers to effective implementation of screening protocols and adherence to recommended respiratory PPE use among healthcare workers."

Cowling, et al. (2010) reviewed the literature on this subject to examine public health preparedness and found some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission. The researchers identified potential barriers to mask and respirator usage, noting, "Considerable resources might be required to make available N95 respirators and other protective equipment to large numbers of healthcare personnel through the course of influenza epidemics or pandemics. Finally, there are likely to be difficulties in ensuring compliance in healthcare workers. Nevertheless personal protective equipment has led to major improvements in general infection control procedures in the hospital setting and should not be discounted due to the lack of available data examining influenza virus outcomes." Cowling, et al. (2010) add that there are fewer data to support the use of masks or respirators to prevent becoming infected and that further studies in controlled settings and studies of natural infections in healthcare and community settings are required to better define the effectiveness of face masks and respirators in preventing influenza virus transmission.

Radonovich, et al. (2008) comment, "The burdensome nature of wearing a respirator has driven controversy on the effectiveness of respiratory protection for healthcare workers for many years. The safety and industrial hygiene communities have insisted on appropriate, dutiful, compulsive practice that includes fit-testing. Legislative amendments have blocked elements such as fit-testing. Most importantly, healthcare workers have pushed back, requesting standards of evidence common in the clinical practice of medicine but almost unheard of in environmental science. The question has been posed: do respirators protect healthcare workers from airborne infectious diseases? In fact, it appears that the correct answer is, 'no one knows.'

Radonovich, et al. (2008) add, "The time has come to invest sufficient resources to determine how well respirators work in the clinical setting. With recent emphasis on public health preparedness for an influenza pandemic, bioterrorism, SARS, and other respiratory infectious diseases, respirators and respiratory-protection programs have become more widely used and stand to become a fixture in infection control. ... We should begin conducting well-designed clinical trials without further delay."

Researchers seem to agree on the fact that additional clinical trials on respirator effectiveness should be conducted, especially seeing that in light of continued potential influenza pandemics and a lack of understanding of the mode(s) of human-to-human transmission, the medical community is debating whether respirators or surgical masks should be used to protect healthcare workers against influenza.
Novak says the 2009 H1N1 pandemic taught healthcare and public health professionals some valuable lessons, including the fact that preparedness was lacking, healthcare workers improperly and inconsistently used PPE in general  and respiratory protection in specific, and that Infection prevention and control practices were not being followed. Because compliance is so problematic, Novak emphasizes that there must be an improved focus on infection control education and the proper use of respiratory protection.

References

Banach DB, Bielang R and Calfee DP. Factors Associated with Unprotected Exposure to 2009 H1N1 Influenza A among Healthcare Workers During the First Wave of the Pandemic. Infect Control Hosp Epidem. Vol. 32, No. 3. March 2011.

Cowling BJ, Zhou Y, Ip DKM, Leung GM and Aiello AE. Face masks to prevent transmission of influenza virus: a systematic review. Epidemiol. Infect. 138, 449-456. 2010.

Department of Health and Human Services. State of the Sector: Healthcare and Social Assistance: Identification of Research Opportunities for the Next Decade of NORA. August 2009.

Mermel LA. The Lancet Infectious Diseases. Vol 9. December 2009.

National Personal Protective Technology Laboratory (NPPTL). NPPTL draft personal protective equipment (PPE) for healthcare workers (HCW) action plan docket #NIOSH-129 [http://www.cdc.gov/niosh/review/public/129/].

Radonovich LJ, Hodgson MJ and Cohen HJ. Do Respirators Protect Health-Care Workers From Airborne Infectious Diseases? Respiratory Care. Vol. 53, No. 12. December 2008.