Limited data suggest N95 respirators, surgical masks provide similar protection

Despite positive reports from analyses performed in laboratory settings, a recent systematic review suggests N95 filtering facepiece respirators may be no more effective in preventing acute respiratory infections among health care workers than surgical masks.

Wide confidence intervals resulting from the small number of relevant studies available for analysis, however, indicate the need for further trials in the health care setting, Jeffrey D. Smith, MSc, of Public Health Ontario, and colleagues wrote in the Canadian Medical Association Journal.

“Randomized controlled trials and observational studies comparing N95 respirators and surgical masks have not shown a benefit, but they may have been underpowered,” they wrote. “The lack of clarity has led to conflicting guideline recommendations regarding respiratory protective equipment for the prevention of acute respiratory infections: N95 respirators are recommended in some guidelines but not others.”

Previous investigations offer conflicting results

Previous studies on the preventive capacity of this equipment have demonstrated mixed outcomes.

In an investigation enrolling 1,441 health care workers published in 2011, C. Raina MacIntyre, PhD, professor of infectious disease epidemiology at the University of New South Wales in Sydney, and colleagues found that workers using N95 respirators reported lower rates of respiratory illness than those wearing surgical masks or no mask use. In contrast, a 2009 analysis by Mark Loeb, MD, MSc, professor in the pathology and molecular medicine department at McMaster University, found surgical masks and N95 respirators to be similar, with an estimated 1% difference in efficacy when preventing influenza among a study cohort of 446 nurses.

Conflicting findings such as these have led to discrepancies between federal and regional health guidelines that may threaten adherence to basic infection control strategies, Smith and colleagues wrote. To settle this, the researchers conducted a meta-analysis of these and other studies gauging the facial protection equipment published from 1990 through 2014. Randomized controlled trials, prospective cohort studies, retrospective cohort studies and case-control studies were eligible for inclusion and subsequently assessed for the quality of their evidence and bias. The primary outcome was laboratory-confirmed respiratory infection, with secondary outcomes including influenza-like illness and workplace absenteeism.

More trials needed to clarify findings

Of the 8,962 titles screened by the researchers, 107 were retrieved for full-text assessment and 31 were considered eligible. Six studies were included in the final analysis: three randomized controlled trials, two case-control studies and one cohort study.

Upon analysis, Smith and colleagues found no difference in the risk for laboratory-confirmed respiratory infection within the randomized controlled trials (OR = 0.89; 95% CI, 0.64-1.24), the cohort study (OR = 0.43; 95% CI, 0.03-6.41) or the case-control studies (OR = 0.91; 95% CI, 0.25-3.36). Combining data from the three observational studies revealed similar findings. Examinations within the three randomized controlled trials for the risk for influenza-like illness or workplace absenteeism also revealed no significant differences between the protective devices. However, a brief summary of 23 surrogate exposure studies identified during the literature search showed N95 respirators to reduce filter penetration, face-seal leakage and total inward leakage when used under laboratory experimental conditions.

These conclusions were restricted by the limited number of available studies, many of overall low quality, Smith and colleagues wrote. While the surrogate exposure studies suggest that N95 respirators are more effective under laboratory conditions, additional randomized controlled trials are needed to fully understand their impact in the clinical setting.

“Although N95 respirators appeared to have a protective advantage over surgical masks in laboratory settings, our 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,” the researchers wrote. – by Dave Muoio

Reference:

Loeb M, et al. JAMA. 2009;doi:10.1001/jama.2009.1466.

MacIntyre CR, et al. Influenza Other Respir Viruses. 2011;doi:10.1111/j.1750-2659.2011.00198.x.

Smith JD, et al. CMAJ. 2016;doi:10.1503/cmaj.150835.

Disclosures: MacIntyre reports funding from CSL Biotherapies and GlaxoSmithKline, and being on advisory boards for GlaxoSmithKline, Merck and Wyeth. Loeb, Smith and colleagues report no relevant financial disclosures. Please see the full study in Influenza and Other Respiratory Viruses for a list of all other authors’ relevant financial disclosures.