The notion that surgical masks provide the same protection from respiratory viruses in a hospital is commonly refuted by lab studies, which show the greater effectiveness of a well-fitted N95 in filtering out aerosols and particles that could go through a standard mask.
As part of its recent annual N95 Day respirator activities, the National Institute for Occupational Safety and Health (NIOSH) sought to bust several myths about respiratory protection, including the misconception that “respirators and surgical masks provide the same type and level of protection for the user.”1
Indeed, NIOSH notes that, “Surgical masks are typically disposable, loose-fitting, and do not form a tight seal to the face. They are also not designed to capture a large percentage of small particles, which means that they cannot prevent the wearer from breathing in airborne particles that may be transmitted by coughs, sneezes, or certain medical procedures (i.e. aerosol-generating procedures). Because of these factors, healthcare workers using surgical masks will not be protected against exposure to airborne transmissible diseases.”
However, actually determining the comparative efficacy of respirators and masks in clinical studies is much more difficult. In a recent meta-analysis, researchers in Canada could find no difference in protection between masks and respirators.2 They reviewed three randomized clinical trials, one cohort study, and two case-control studies.
“No significant difference in risk of laboratory-confirmed respiratory infection was detected between healthcare workers using N95 respirators and those using surgical masks in the meta-analysis of the randomized trials,” the authors concluded. “It was not surprising to find that N95 respirators were generally more efficient filters with better face-seal characteristics than surgical masks when tested in the laboratory. However, transmission of acute respiratory infections is a complex process that may not be appropriately replicated by surrogate exposure studies.”
Fit-test Woes?
A contributing factor is likely that respirator use is compromised by a lack of adequate fit-testing, and workers may handle and readjust the equipment during use.
“N95 respirators are often considered uncomfortable for regular use, and improper wearing or adjustment of the respirator because of discomfort could lead to inadvertent face contamination, thus negating the potential protective benefit,” the researchers found.
Still, the authors concluded in the paper that “randomized controlled trials conducted in clinical settings represent the most valid information to evaluate the effectiveness of N95 respirators. They are more relevant to real clinical situations and report actual outcomes in healthcare workers, and therefore they are the best evidence on effectiveness to inform policy-making.”
HIC could not reach the lead author of the study as this issue went to press, but two NIOSH scientists commented jointly via email on the study: Deborah Novak, PhD, RN, and Ronald Shaffer, PhD, both of NIOSH’s National Personal Protective Technology Laboratory in Pittsburgh.
“We are aware of the meta-analysis published earlier this year,” Novak and Shaffer noted. “The article shares several similar themes as a paper3 with NIOSH co-authors that addresses this same topic. For example, both papers report that across many laboratory studies, N95 filtering facepiece respirators (FFRs) show less filter penetration, less face-seal leakage, and less total inward leakage than surgical masks and that randomized controlled trials (RCTs) are important.”
“However, the RCTs completed to date have yielded inconclusive results because of limitations in experimental design and implementation,” they added. “For example, study subjects failing to wear the assigned device during all times of potential exposure (i.e., poor compliance with the intervention) negate the superior fit and filtration properties of the FFR. Current studies such as ResPECT4 may be able to overcome some of these difficulties, but a complete face-fitting respirator vs. surgical mask clinical trial remains elusive.”
Indeed, in the recently published ResPECT study, the authors concluded, “While it may seem that N95 respirators should better protect healthcare personnel (HCPs) than medical masks against airborne infections in the workplace, this notion has not been validated by objective clinical evidence. Low tolerance to respirator wear among HCPs may prompt more frequent or longer periods of removal, compared to medical masks, to an extent that the benefits of higher levels of filtration and lower levels of leakage around the facial seal afforded by respirators are offset or subjugated.”
REFERENCES
- Preparedness through Daily Practice: The Myths of Respiratory Protection in Healthcare. DHHS (NIOSH) Publication No. 2016–109. March 2016:http://bit.ly/2cB80Sq.
- Smith JD, MacDougall CC, Johnstone J, et al. Effectiveness of N95 respirators versus surgical masks in protecting healthcare workers from acute respiratory infection: A systematic review and meta-analysis. CMAJ, published ahead of print March 7, 2016, doi:10.1503/cmaj.150835.
- Janssen L, Ettinger H, Graham S, et al. Commentary: The Use of Respirators to Reduce Inhalation of Airborne Biological Agents. Journal of Occupational and Environmental Hygiene 2013;10:8, D97-D103, DOI: 10.1080/15459624.2013.799964.
- Radonovich, JJ Jr, Bessesen MT, Cummings DA, et al. The Respiratory Protection Effectiveness Clinical Trial (ResPECT): A cluster randomized comparison of respirator and medical mask effectiveness against respiratory infections in healthcare personnel. BMC Infectious Diseases 2016;16:243 DOI 10.1186/s12879-016-1494-2.
