Respiratory Protection Provided By N95 Respirators Vs Disposable Medicine Masks Against Airborne Bateria

Backgroud: N95 filtering facepiece respirators(FFR) and disposable medicine masks(DMM) are the most widely used respiratory protective equipment recently. They were often used to protect health care workers as well as the general public against harmful airborne dusts and microorganisms. While the superior filtration and fit performance of N95 FFR over DMM have been demonstrated in previous studies with non-biological particles(i.e. dusts, smokes and inhalable particulate), their superiority in bio-aerosol protection and reducing disease transmission remain controversial. Previous studies using different research methods have yielded inconsistent conclusions. There is still no properly designed study protocol to evaluate the practical protective effect of microbial aerosol of FFR and DMM. Summed up the experience and shortage of previous study, the current study attempts to investigate the relative efficacy of the two devices by combining laboratory study with workplace study.Objective: To determine the relative protection provided by N95 filtering facepiece respirators and disposable medicine masks against airborne bacteria in different working environments; To analysis the factors that affect bacteria filtration of respirator; To give advice to futher improve the microbial aerosol respiratory protection.Methods: Bacterial filtering efficiency(BFE) and particulate filtering efficiency(PFE) were measured using the JWL-2A Sampler and TSI PortaCount 8038. The field study was performed in hospital and campus with 12 subjects wearing an N95 filtering facepiece respirator and a disposable medicine mask in each working environment for 1h, respectively. Airborne microorganisms and bacteria samples from both the external(Ce) and the inner(Ci) surface of N95 FFR and DMM are collected. The Ce: Ci ratio was used to calculate the bacterial filtering proportion. The field study was performed in both summer and winter.Results: Both BFE and PFE of N95 FFR were higher than that of DMM. There was significant difference between the two materials(P < 0. 05). The BFE and PFE of both devices measured while air pump ran at a rate of 20L/min showed a significant interaction. In summer, airborne bacterial concentration was higher than that in winter. In the same season, airborne bacterial concentration in hospital environment is higher than that in campus. The higher the airborne bacterial concentration, the greater bacterial contaminated on the external surface of the used masks. To all masks used in different working environment, bacterial contamination on the external surface was much greater than the inner surface(P < 0.01). Compared to N95 FFR, DMM had slighter bacterial contamination on the external surface and greater bacterial contamination on the inner surface. However, this difference was not significant(P > 0.05). The bacterial filtering proportion of N95 FFR is higher than DMM. These differences were significant in samples tested in summer(P < 0.05), but were not significant in samples tested in winter(P > 0.05).Conclusion: Superior filtration with airborne bacteria and particulate of N95 FFR material were found over DMM material. Accordingly, workplace study showed that bacterial filtering efficiency of N95 respirator is superior to medicine mask, and this advantage become more obvious in high airborne bacterial concentration levels.