Respirators Not More Effective Than Masks in the Workplace

Pam Harrison

March 09, 2016

N95 respirators may not be more effective than surgical masks in preventing transmission of acute respiratory infections to healthcare workers under normal working conditions, although they may be more effective in surrogate exposure environments, a meta-analysis suggests.

"N95 respirators are recommended in some guidelines but not others.... Conflicting recommendations from federal and provincial health authorities lead to confusion among heath care workers, which can result in lack of adherence to basic infection control principles and practices," Jeffrey D. Smith, MSc, from Public Health Ontario, Toronto, Canada, and colleagues write in an article published online March 7 in the Canadian Medical Association Journal.

"[O]ur meta-analysis showed that there were insufficient data to determine definitively whether N95 respirators are superior to surgical masks in protecting health care workers against transmissible acute respiratory infections in clinical settings."

Investigators included three randomized clinical trials, one cohort study, and two case–control studies in their systematic review. They also analyzed 23 surrogate exposure studies. In the meta-analysis of the clinical trials, Smith and colleagues were unable to identify any significant difference between patients who wore a N95 respirator and those who wore surgical masks in the risk of acquiring a confirmed respiratory infection or an influenza-like illness.

They also observed no difference in rates of reported workplace absenteeism between workers who donned a N95 respirator at work and those who chose to wear a surgical mask.

Surrogate Exposure Studies

Of the 23 surrogate exposure studies analyzed by the Canadian group, "N95 respirators showed less filter penetration, less face-seal leakage and less total inward leakage under the laboratory experimental conditions described," the team reports. That said, Smith and colleagues caution that the transmission of any acute respiratory infection in the workplace setting may not be easily or accurately replicated in an experimental setting such as a surrogate exposure study.

Furthermore, it is recommended that healthcare workers who wear a N95 respirator make sure the face seal is appropriately fitted to their face, as a good seal is important to how well a N95 respirator functions. If a worker adjusts the respirator because it is uncomfortable to wear, that "could lead to inadvertent face contamination," the authors caution.

They also note that with the exception of a single, randomized controlled trial included in the meta-analysis, no study audited compliance with the intervention, and any respiratory infection reported by workers in the studies analyzed may have been acquired in the community, and not in the hospital setting.

In addition, "these results are not generalizable to infections transmitted primarily through airborne routes (i.e., tuberculosis, measles and varicella) or to protection from acute respiratory infections during aerosol-generating medical procedures," the researchers explain.

The investigators thus conclude that more and larger randomized controlled trials should be carried out to detect a potentially important difference in the degree of protection afforded to healthcare workers who use a N95 respirator vs those who wear a surgical mask.

"Randomized controlled trials conducted in clinical settings represent the most valid information to evaluate the effectiveness of N95 respirators," Smith and colleagues conclude.

"They are more relevant to real clinical situations and report actual outcomes in health care workers, and therefore they are the best evidence on effectiveness to inform policy-making."

The authors have disclosed no relevant financial relationships.

CMAJ. Published online March 7, 2016. Full text

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