Surgical Masks vs Respirators
Surgical masks and respirators are different and were devised for different purposes. The biggest difference between surgical masks and respirators is their intended use. Surgical masks were designed to protect the sterile field and work environment from spit and mucous generated by the wearer. Respirators were designed to protect the wearer from the inhalation of airborne contaminants generated from nearby sources. The protection offered by either device depends on the efficiency of the filter (how well the filter collects airborne particles) and the fit (seal between the facepiece and the face). The US Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) do not consider surgical masks to be respiratory protection devices.
Surgical masks are cleared for marketing by the US Food and Drug Administration (FDA), but the FDA does not test their performance. Manufacturers must demonstrate only that a new mask is at least as good as any mask currently on the market; no assessment of fit is required. Surgical masks are not designed to pass a fit test or to be evaluated for fit, nor can they be properly fitted to the face or tested for fit. Without a good fit and seal, leakage occurs around the edge of the mask when the wearer inhales. Even the best filter will not provide good protection to the wearer if the fit is not adequate because air will leak around the mask and unfiltered air will be inhaled.
Surgical masks offer some protection for the mucous membranes of the nose and mouth of the wearer from large droplets and splashes but will not protect against inhalation of aerosols. The filtering efficiency of available masks varies widely; most do not effectively filter small particles from the air, and many studies have demonstrated the poor filter performance of single (or even multiple) surgical masks.[7,8,9,10,11,12,13]
Respirators such as N95 filtering facepiece respirators or elastomeric respirators with N95 filters are devices that are tested and certified by NIOSH to provide at least 95% filtration of 0.3-µm particles. A certified respirator filter will have much higher efficiency at particle sizes both smaller and larger than the test size. Therefore, because a respirator filter offers very good protection, the most important aspect of respirator protection is how well it fits and seals to the face.
Fit and Seal
It is possible to measure the degree of protection offered by a properly fitted respirator by qualitative or quantitative methods, which are described in detail in the OSHA Respiratory Protection Standard. A well-fitting NIOSH-certified half-facepiece air-purifying respirator (such as an N95 filtering facepiece respirator) must provide an assigned protection factor of at least 10, which means that the respirator must offer for most wearers a 10-fold decrease in the external particle concentration. Because each person's face is different, fit testing is required to ensure that a respirator model and size will offer this level of protection when worn in the workplace. When quantitative fit testing is performed for an individual respirator wearer, the fit factor (outside divided by inside concentration) must be at least 10 times greater than the assigned protection factor of 10. Thus, the respirator must have a fit factor of 100; the 10-fold safety margin recognizes that fit in a controlled laboratory setting is likely to be better than fit experienced when the respirator is worn during work.
As one might expect from the differences in purpose, design, and testing, studies have demonstrated that respirators provide significantly greater wearer protection from inhalable aerosols than surgical masks. For example, a recent NIOSH study compared the performances of 15 N95 elastomeric respirators, 15 N95 filtering facepiece respirators, and 6 surgical masks. The highest level of protection was found with the elastomeric N95 respirators, followed by the filtering facepiece N95 respirators; the lowest protection was found with surgical masks.
In another study, the fit performance of surgical masks with relatively good filters (although with much lower filter performance than required by NIOSH) was much less than the minimum required for half-facepiece air-purifying respirators. All participants failed qualitative fit tests using the bitter-tasting Bitrex® (Johnson Matthey, London, UK) aerosol and quantitative tests using a Portacount® (TSI Inc., Shoreview, MN). Quantitative fit tests showed an average fit factor ranging from 4 to 6. OSHA requires a minimum quantitative fit factor of 100 for a half-facepiece air-purifying respirator.
These studies demonstrate that surgical masks should never be used to protect healthcare workers from inhalation of airborne infectious aerosols because their filters are not designed to prevent passage of small particles. Moreover, even if a surgical mask has a "better" filter, the lack of a close seal to the face will negate filter performance because particles will follow the path of least resistance and travel through the gaps between the surgical mask and the face.
Although it has been difficult to study the efficacy of surgical masks and N95 respirators for the protection of HCP against influenza in real-world settings, 2 such studies have recently been published. The first study by Loeb and colleagues was published in JAMA in 2009. In this noninferiority randomized controlled trial, 446 nurses in 8 Ontario hospitals were assigned to wear either a fit-tested N95 respirator or a surgical mask when providing care to patients with febrile respiratory illness during the 2008-2009 influenza season.
The investigators concluded that the use of a surgical mask compared with an N95 respirator resulted in noninferior rates of laboratory-confirmed influenza; however, this conclusion is inconsistent with some of the stated study findings indicating that the relative risks for influenza-like illness and fever were in favor of N95 respirators being more protective. "Nine nurses (4.2%) in the surgical mask group and 2 nurses (1.0%) in the N95 respirator group met our criteria for influenza-like illness (absolute risk difference, -3.29%; 95% confidence interval, -6.31% to 0.28%; P = .06). All 11 had laboratory-confirmed influenza. Significantly more nurses in the surgical mask group (12, or 5.66%) reported fever compared with the N95 respirator group (2, or 0.9%; P = .007)." The most important shortcomings of this study were: (1) lack of information about exposure (eg, number of patients cared for; status of patient illness), and (2) failure to adequately observe respirator or surgical mask use. It is thus impossible to state that the comparison groups were similar in either level of exposure or amount of protection available during exposure.
In February 2011, MacIntyre and colleagues published a study comparing the efficacy of surgical masks with that of N95 respirators. In this cluster randomized clinical trial, 1441 HCP in 15 Beijing hospitals wore surgical masks or respirators during their entire work shift for 4 weeks during the 2008-2009 influenza season. Although results were not statistically significant, rates of infection in the surgical mask group were double that in the N95 group, suggesting that a benefit is conferred by respirators. In this study, adherence to mask or respirator use was monitored by observation and by self-report.
It may be difficult to detect statistically significant differences in efficacy between surgical masks and N95 respirators when influenza is present in the community because HCP can become infected with influenza or other respiratory illnesses both inside and outside of the workplace, which could obscure any difference in the efficacy of the 2 devices. Even in the workplace, HCP can be exposed to influenza by nonpatients, including visitors and coworkers. It is unlikely that a study will ever be conducted in a closed setting in which the only exposure of HCP to influenza could be through infected patients.
Recommendations for Masks and Respirators
On November 5, 2009, shortly after the online publication of the study by Loeb and colleagues, the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, and the Association for Professionals in Infection Control jointly issued a letter to President Obama urging him to modify the federal PPE guidance for H1N1 and recommend surgical masks for routine H1N1 patient care. In September 2010, CDC issued updated infection control guidance for influenza (including 2009 H1N1) and recommended that surgical masks be used for routine care of patients with influenza but that N95 respirators or a higher level protection be used by HCP performing aerosolizing procedures on such patients. In Dr. John Bartlett's Medscape review of the Top Ten Infectious Disease Hot Topics: 2010-2011 he stated that, "The long controversy over the relative merits of surgical vs N95 masks was finally resolved in the study by Loeb and colleagues, which showed that surgical masks were as effective as the N95 masks. The CDC changed their guidelines accordingly."
Medscape Infectious Diseases © 2011
Cite this: Kathleen H. Harriman, Lisa M. Brosseau. Controversy: Respiratory Protection for Healthcare Workers - Medscape - Apr 28, 2011.