FAQ: What is the evidence supporting masking as an effective preventive strategy for patient safety?

Some healthcare institutions have adopted masking policies as part of their influenza reduction strategies. In some cases, masking is offered as an alternative to immunization and/or as a requirement when influenza immunization is either refused or not indicated for the HCP. Here are some general questions about masking:

What is the evidence supporting masking as an effective preventive strategy for patient safety? Are such policies working where they have been implemented as part of mandated programs or otherwise[FAQ Date: April 1, 2013]

The available literature suggests that a combination of masks and hand hygiene can provide protective benefit (reducing ILI hazard) in selected settings. Some work has compared the effectiveness of different mask technologies N95 respirators vs. masks, etc. We are not aware of studies that offer precise metrics on specific health care setting or that measure program performance where masks are used in lieu of vaccinations for HCP that either cannot receive vaccination for medical reasons or who decline for other reasons. The citations and abstracts/excerpts below may be helpful.


Surgical Mask vs N95 Respirator for Preventing Influenza Among Healthcare Workers: A Randomized Trial
Mark Loeb, MD, MSc; Nancy Dafoe, RN; James Mahony, PhD; Michael John, MD; Alicia Sarabia, MD; Verne Glavin, MD; Richard Webby, PhD; Marek Smieja, MD; David J. D. Earn, PhD; Sylvia Chong, BSc; Ashley Webb, BS; Stephen D. Walter, PhD
Vol. 302 No. 17, pp. 1839-1926, Nov. 4, 2009

Context  Data about the effectiveness of the surgical mask compared with the N95 respirator for protecting healthcare workers against influenza are sparse. Given the likelihood that N95 respirators will be in short supply during a pandemic and not available in many countries, knowing the effectiveness of the surgical mask is of public health importance.

Objective  To compare the surgical mask with the N95 respirator in protecting healthcare workers against influenza.

Design, Setting, and Participants  Noninferiority randomized controlled trial of 446 nurses in emergency departments, medical units, and pediatric units in 8 tertiary care Ontario hospitals.

Intervention  Assignment to either a fit-tested N95 respirator or a surgical mask when providing care to patients with FAQ Date: rile respiratory illness during the 2008-2009 influenza season.

Main Outcome Measures  The primary outcome was laboratory-confirmed influenza measured by polymerase chain reaction or a 4-fold rise in hemagglutinin titers. Effectiveness of the surgical mask was assessed as noninferiority of the surgical mask compared with the N95 respirator. The criterion for noninferiority was met if the lower limit of the 95% confidence interval (CI) for the reduction in incidence (N95 respirator minus surgical group) was greater than –9%.

Results  Between September 23, 2008, and December 8, 2008, 478 nurses were assessed for eligibility and 446 nurses were enrolled and randomly assigned the intervention; 225 were allocated to receive surgical masks and 221 to N95 respirators. Influenza infection occurred in 50 nurses (23.6%) in the surgical mask group and in 48 (22.9%) in the N95 respirator group (absolute risk difference, –0.73%; 95% CI, –8.8% to 7.3%; P = .86), the lower confidence limit being inside the noninferiority limit of –9%.

Conclusion  Among nurses in Ontario tertiary care hospitals, use of a surgical mask compared with an N95 respirator resulted in noninferior rates of laboratory-confirmed influenza.

Trial Registration  clinicaltrials.gov Identifier: NCT00756574

Surgical Masks for Protection of Healthcare Personnel against Pandemic Novel Swine-Origin Influenza A (H1N1)–2009: Results from an Observational Study
Brief Report
Clinical Infectious Diseases
1 April 2010   Volume 50, Number 7
There is ongoing debate about the efficacy of surgical masks versus N95 respirators for protection against pandemic novel swine-origin influenza A (H1N1)–2009. Our hospital, which is designated to manage outbreaks of emerging infection, has robust surveillance systems to detect infection in staff. The incidence of pandemic H1N1-2009 remained low in staff with use of surgical masks.

Unmasking the Confusion of Respiratory Protection to Prevent Influenza-Like Illness in Crowded Community Settings
Titus L. Daniels and Thomas R. Talbot
Editorial Commentaries
Journal of Infectious Diseases
Volume 201, Number 4 (February 15, 2010)
…Fortunately, several well-designed in vivo studies have now been published that conclude there is no significant advantage of one mask type over another for respiratory protection against influenza or ILI. Loeb et al [10] conducted a noninferiority randomized, controlled study of mask use among nurses in Ontario, Canada, which demonstrated that the attack rate of laboratory-confirmed influenza was not different between those who wore facemasks and those who wore N95 respirators as respiratory protection (23.6% vs 22.9%, respectively). Although unable to demonstrate a protective benefit of mask use in households, MacIntyre et al [3] did note that adherence to mask use (face mask or N95 respirator) was associated with a reduction in ILI (hazard ratio, 0.26; 95% CI, 0.09–0.77).

Taken together with the Aiello et al [1] study, these data suggest that influenza transmission and ILI can be effectively interrupted with the use of a face mask and hand hygiene in settings of close contact. In addition, these data could inform the ongoing debate concerning respiratory protection for HCPs. Although the majority of data supporting prevention of influenza transmission with face masks has been derived from community sites, interactions between HCPs and patients are generally of a magnitude similar to what would be encountered in domestic settings. One could even argue that the household setting poses greater risk of transmission as a result of continued, prolonged exposure, whereas most HCP encounters with patients are brief, albeit possibly more frequent.

Aiello et al [1] have conducted a well-designed cluster randomized study demonstrating that use of a face mask combined with hand hygiene in a crowded community setting is helpful in preventing ILI. Although it would be difficult to extrapolate these data to the general public in noncrowded conditions (i.e., nonresidential settings), these data can inform policy makers on the recommendations for mask use in community settings and perhaps other settings (e.g., healthcare institutions)…


Facemasks, Hand Hygiene, and Influenza among Young Adults: A Randomized Intervention Trial
Allison E. Aiello, Vanessa Perez, Rebecca M. Coulborn, Brian M. Davis, Monica Uddin, Arnold S. Monto
PLoS ONE: Research Article, published Jan. 25, 2012 10.1371/journal.pone.0029744
Limited vaccine availability and the potential for resistance to antiviral medications have led to calls for establishing the efficacy of non-pharmaceutical measures for mitigating pandemic influenza. Our objective was to examine if the use of face masks and hand hygiene reduced rates of influenza-like illness (ILI) and laboratory-confirmed influenza in the natural setting. A cluster-randomized intervention trial was designed involving 1,178 young adults living in 37 residence houses in 5 university residence halls during the 2007–2008 influenza season. Participants were assigned to face mask and hand hygiene, face mask only, or control group during the study. Discrete-time survival models using generalized estimating equations to estimate intervention effects on ILI and confirmed influenza A/B infection over a 6-week study period were examined. A significant reduction in the rate of ILI was observed in weeks 3 through 6 of the study, with a maximum reduction of 75% during the final study week (rate ratio [RR] = 0.25, [95% CI, 0.07 to 0.87]). Both intervention groups compared to the control showed cumulative reductions in rates of influenza over the study period, although results did not reach statistical significance. Generalizability limited to similar settings and age groups. Face masks and hand hygiene combined may reduce the rate of ILI and confirmed influenza in community settings. These non-pharmaceutical measures should be recommended in crowded settings at the start of an influenza pandemic.
Trail Registration
Clinicaltrials.gov NCT00490633

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