Effectiveness of N95 respirators versus surgical masks in protecting health care workers from acute respiratory infection: a systematic review and meta-analysis

Jeffrey D. Smith; Colin C. MacDougall; Jennie Johnstone; Ray A. Copes; Brian Schwartz; Gary E. Garber

doi:10.1503/cmaj.150835

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The case of influenza
Raymond Tellier

Posted on: 04 July 2016
N95 versus surgical masks
Sergey A Grinshpun

Posted on: 21 April 2016
Re:Failure to understand worker protection
Gabor Lantos

Posted on: 06 April 2016
Failure to understand worker protection
Linda Haslam-Stroud

Posted on: 22 March 2016
NIOSH re surgical masks
Gabor Lantos

Posted on: 10 March 2016

Posted on: (4 July 2016)

The case of influenza
Raymond Tellier, Associate Professor
I read with interest the article of Smith et al. Regarding Influenza, I must note the following:
1) In their meta analysis of N-95 respirators vs surgical masks, Smith et al place a heavy reliance on the study of Loeb et al [1] . A careful reading of Loeb et al shows that 42 % of their infected subjects (10% of studied nurses) were infected with A(H1N1) pdm09 and had been infected prior to approximately May 1, 2...
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I read with interest the article of Smith et al. Regarding Influenza, I must note the following:
1) In their meta analysis of N-95 respirators vs surgical masks, Smith et al place a heavy reliance on the study of Loeb et al [1] . A careful reading of Loeb et al shows that 42 % of their infected subjects (10% of studied nurses) were infected with A(H1N1) pdm09 and had been infected prior to approximately May 1, 2009 . All these infections were diagnosed by serology only, none were PCR positive. By comparison, a study of the first wave of the 2009 pandemic in Ontario, published in 2009 by the Ontario Agency for Health Protection and Promotion [2] documents that by May 1, 2009 there had been a little less than a hundred laboratory confirmed cases (by PCR) of A(H1N1) pdm 09 in the whole province, half of which having been acquired abroad, and that the first wave was just beginning to ramp up. The discrepancy would suggest a considerably accelerated transmission within hospitals early in the pandemic; however it is remarkable that none of the cases reported by Loeb et al were confirmed by PCR. It is now documented that the hemagglutination inhibition serology for A(H1N1) pdm09 shows considerable cross reactivity with the previous seasonal A(H1N1) (and possibly with other strains of influenza) [3] and so these instances of seroconversions could have been conceivably caused by infections acquired earlier in the community with the seasonal A(H1N1), or even by vaccination. This suggests that the data from Loeb et al should be re-analyzed without these cases; of course the remaining seroconversions to seasonal influenza might well have been acquired in the community rather than at the hospital, leaving us with little firm support for the contention that surgical masks are non inferior to N95 respirators.
2) Smith et al misrepresent the study of Milton et al [4] when they state that infected humans " ... rarely produce aerosols that contain infectious viral particles". Numerous studies have detected by PCR aerosolized influenza viruses produced by infected humans. It is well known that isolation of influenza viruses in cell culture is considerably less sensitive than detection by PCR; furthermore, recovery of aerosol particles using collectors adversely affects the infectivity of viruses [5]. Thus, detection by culture of infectious influenza virus in aerosols in any amount is bound to be a significant underestimate, as well as a cause for serious concern. I note that several other studies have also reported the detection of infectious influenza viruses by culture in aerosols produced by infected patients, e.g. [6-8].
References
[1] Loeb M, Dafoe N, Mahony J, John M, Sarabia A, Glavin V, et al. Surgical mask vs N95 respirator for preventing influenza among health care workers: a randomized trial. JAMA. 2009;302(17):1865-71.
[2] Ontario Agency for Health Protection and Promotion. Epidemiological summary of pandemic influenza A(H1N1) 2009 virus - Ontario, Canada, June 2009. Wkly Epidemiol Rec. 2009;84(47):485-91.
[3] Freeman G, Perera RAPM, Ngan E, Fang VJ, S C, Ip DKM, et al. Quantifying homologous and heterologous antibody titre rises after influenza virus infection. Epidemiology and Infection. 2016:doi.org/10.1017/S0950268816000583.
[4] Milton DK, Fabian MP, Cowling BJ, Grantham ML, McDevitt JJ. Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical masks. PLoS Pathog. 2013;9:e1003205.
[5] Tseng C-C, Li C-S. Collection efficiency of aerosol samplers for virus-containing aerosols. J Aerosol Sci. 2005;36:593-607.
[6] Lindsley WG, Blachere FM, Thewlis RE, Vishnu A, Davis KA, Cao G, et al. Measurements of airborne influenza virus in aerosol particles from human cough. PLoS One. 2010;5(11):e15100.
[7] Lednicky JA, Loeb JC. Detection and isolation of airborne influenza A H3N2 virus using a Sioutas personal cascade impactor sampler. Influenza Res Treat. 2013:doi: 10.1155/2013/656825.
[8] Lindsley WG, Blachere FM, Beezhold DH, Thewlis RE, Noorbakhsh B, Othumpangat S, et al. Viable influenza A virus in airborne particles expelled during coughs vs exhalations. Influenza Other Respir Viruses. 2016:doi:10.1111/irv.12390.
Conflict of Interest:
None declared
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Competing Interests: None declared.
Posted on: (21 April 2016)

N95 versus surgical masks
Sergey A Grinshpun, university professor
Given the wealth of published data on the efficiency of N95 FFRs and surgical masks resulting from various extensive experimental studies, it is surprising to learn that the investigators of this paper found no evidence that N95 respirators offer better protection compared to surgical masks. Our testing conducted with health care workers showed a clear difference. I would echo Dr. Lantos' comment "the absence of proof i...
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Given the wealth of published data on the efficiency of N95 FFRs and surgical masks resulting from various extensive experimental studies, it is surprising to learn that the investigators of this paper found no evidence that N95 respirators offer better protection compared to surgical masks. Our testing conducted with health care workers showed a clear difference. I would echo Dr. Lantos' comment "the absence of proof is not the proof of absence." Of course, more has to be done to improve the N95 FFRs, especially though improving the faceseal, but the health care community should be aware of a very low (if any) efficiency of surgical masks against aerosol particles while N95 have demonstrated significantly higher protection.
Conflict of Interest:
None declared
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Competing Interests: None declared.
Posted on: (6 April 2016)

Re:Failure to understand worker protection
Gabor Lantos, Occupational physician
Further to Ms. Haslam-Stroud's comments, Justice Campbell also emphasized the Precautionary Principle which is still, 13 years later, all too much lacking; as most recently evidenced by the inadequate protection of nurses against Ebola in the USA. Both the SARS Commission and the later CSA Z94.4-11 standard clearly indicate the need for a Respiratory Safety Officer, which most hospitals still do not have, and the standard...
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Further to Ms. Haslam-Stroud's comments, Justice Campbell also emphasized the Precautionary Principle which is still, 13 years later, all too much lacking; as most recently evidenced by the inadequate protection of nurses against Ebola in the USA. Both the SARS Commission and the later CSA Z94.4-11 standard clearly indicate the need for a Respiratory Safety Officer, which most hospitals still do not have, and the standard also utilizes "control banding", which if followed, would immediately exclude the use of surgical masks in infectious clinical settings. Both the premise and the conclusions of the meta-analysis are not in keeping with the Precautionary Principle. The meta-analysis reviewed the wrong studies; poorly conducted clinical studies instead of peer-reviewed scientific ones in areas such as occupational hygiene, biosafety, aerosol physics, and respiratory protection.
Conflict of Interest:
None declared
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Competing Interests: None declared.
Posted on: (22 March 2016)

Failure to understand worker protection
Linda Haslam-Stroud, President
In the SARS Commission report, "Spring of Fear," Justice Archie Campbell wrote, "There were two solitudes: infection control and worker safety....infection control failed to protect nurses..."
To the detriment of health-care workers and their patients across Ontario, this divide between the two solitudes has been permitted to persist.
The opening sentence in this CMAJ paper's abstract reveals infectio...
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In the SARS Commission report, "Spring of Fear," Justice Archie Campbell wrote, "There were two solitudes: infection control and worker safety....infection control failed to protect nurses..."
To the detriment of health-care workers and their patients across Ontario, this divide between the two solitudes has been permitted to persist.
The opening sentence in this CMAJ paper's abstract reveals infection control's continuing failure to understand fundamental worker protection. It talks about determining what "...facial protection should be used by health-care workers to prevent transmission of acute respiratory infection." Then it goes on to explain the research into the comparative protective abilities between an approved N95 respirator and a surgical mask, which isn't recognized anywhere in science-based standards as a form of respiratory protection.
If the researchers wanted to look at facial protection they should have examined visors, goggles and hoods, etc., not an N95, which while worn on the face, and which may provide a limited physical barrier, is not designed as facial protection.
On the other hand, if respiratory protection is the question, then yes, the N95, widely used in health-care, is an appropriate starting point. It is the lowest, scientifically and legally acceptable form of personal equipment for protecting workers from inhaling harmful particles. But why compare them to surgical masks? While also worn on the face, surgical masks were never designed, tested or approved to protect the wearer. Their function is to prevent the wearer from expelling contaminants, e.g. onto a patient or a sterile field.
The conclusion, as confounding to me as the faulty starting point of this research, is that the lowest form of respirator, the N95, doesn't appear to work in health-care settings. If valid, that means we need to determine why not and focus on solutions like fit-testing, education, training and even developing an ergonomic design better suited to health care. It cannot mean we take away real respirators from health-care workers.
Despite this, the authors seem to want to waste more time on building randomized control trials to compare respiratory protective capability between the N95, a respirator they say doesn't work, and the surgical mask, something that isn't even a respirator. One really has to ask what ethics board would ever approve sending a control group of healthy workers into a room contaminated with airborne disease wearing surgical masks, which are not actual respirators. Furthermore, what would be the point?
A true respiratory protection program, as outlined in Canadian Standards Association standard Z94.4-11, should be a key component of a comprehensive infection control program that controls risk to health-care workers and their patients. In accordance with the hierarchy of controls, personal protective equipment (PPE) like a respirator is the last line of defence against a hazard, and the responsible action when you've proven PPE doesn't do the job is to find out why and correct it, not remove the last thing standing between a worker and harm.
If a particular gown allows fluid penetration when dealing with bodily fluids, do you take it off and abandon protection altogether? Or do you look for something that will better protect the worker? When facing the risk of exposure to an inhalable contaminant, there is no legal or ethical foundation for reverting to absolutely no respiratory protection, which is what a surgical mask represents.
I frankly do not agree that anyone has proven N95s can't work in health care. With proper training, reinforcement, staffing and other support (all components of a legally required respiratory protection program, none of which were controlled for in the cited studies) N95s have a proven track record. In limited situations they can be very effective in protecting respiratory tracts of wearers, as evinced in their use in British Columbia where SARS was stopped in its tracks, and in tuberculosis treatment around the world.
No one knows better than front-line nurses that the N95 is not a perfect fit for health-care settings and can be very uncomfortable to use. But nurses and other health-care workers deserve to be protected. As we face a future laden with all kinds of potential threats from natural emerging diseases and bioterrorism, wouldn't our limited time and resources be better spent focusing our research and response efforts on developing respirators that will better protect health care workers?
Linda Haslam-Stroud, RN, President, Ontario Nurses' Association
Conflict of Interest:
None declared
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Competing Interests: None declared.
Posted on: (10 March 2016)

NIOSH re surgical masks
Gabor Lantos, P.Eng, MD
The absence of proof is not the proof of absence. There is much evidence in the aerosol physics and bioaerosol literature re airborne spread from coughs and sneezes. There is a good reason why NIOSH has never approved surgical masks as PPE.
Conflict of Interest:
None declared

Competing Interests: None declared.