Various studies yielded conflicting results
NEW YORK (Reuters Health) - Although N95 respirators may appear to offer health care workers a protective advantage over surgical masks in laboratory settings, the data don't show definitively that this is the case, according to Canada-based researchers.
Various studies have compared N95 respirators to surgical masks, but these have yielded "conflicting" results, the researchers wrote, in an article online March 7 in CMAJ, the Canadian Medical Association Journal. The "lack of clarity has led to conflicting guideline recommendations regarding respiratory protective equipment for the prevention of acute respiratory infections."
To investigate further, Dr. Gary Garber, chief, infection prevention and control, Public Health Ontario, Toronto, and colleagues conducted a meta-analysis that included six randomized controlled trials comparing the two forms of protection and, separately, 23 surrogate exposure studies. The latter compared N95 respirators and surgical masks using manikins or adult volunteers in simulated conditions.
In the meta-analysis of the clinical studies, the researchers found no significant difference between the respirators and the surgical masks in associated risk of laboratory-confirmed respiratory infection, influenza-like illness, or reported workplace absenteeism.
In the surrogate exposure studies, N95 respirators were associated with less filter penetration, less face-seal leakage, and less total inward leakage compared with surgical masks.
Although there appeared to be a protective advantage to the N95 respirators in the surrogate studies, 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 authors reported.
"N95 respirators were developed to improve the protection against airborne pathogens such as tuberculosis or measles," Dr. Garber told Reuters Health by email. "However, most acute respiratory pathogens are not airborne, but are spread through droplets and our contact with these droplets, which are released when someone coughs or sneezes. Thus, the emphasis should be on preventing contact with the face, mouth, and eyes. This can be achieved through routine masking, gloves, and proper hand hygiene, which is most often not recognized for its pivotal role in health protection."
Dr. Kathryn Boling, of Mercy Medical Center, Baltimore, told Reuters Health by email, "In the real world, I think we have to tell health care workers that the jury is still out, but it is likely safe to wear a mask for lower risk infections that are not primarily spread through droplets. However, this does not prove it is safe to just abandon the respirator."
"There are limitations to this meta-analysis," she said, "including that almost all of the studies did not audit compliance; confounding factors such as other protective gear such as gloves and gowns were not taken into consideration; study participants might have been exposed outside of the clinical setting (in the community); respirators might have become contaminated and caused transmission; and the results looked at low-droplet respiratory transmission and are not generalized to infections transmissible primarily by airborne droplets, such as varicella, measles and tuberculosis."
Dr. Boling added that "individual institutional policy will dictate what protection is required for which infections unless public health concerns, as in the case of Ebola, make a more general declaration necessary."
Dr. Garber observed, "N95 respirators are more expensive, and the required fit testing to ensure a proper seal to the face adds additional expense. An institution would need to stock different models of N95 respirators because each individual may get an optimal fit with a different respirator. An individual or organization may decide to use N95 respirators for acute respiratory infections such as influenza or pandemic influenza, but our data does not show improved protection in clinical studies."
Dr. Garber also emphasized that "the use of respiratory protective equipment is just one component of an infection-control program. Other components are necessary to adequately control risk to healthcare workers."
