Challenge of N95 Filtering Facepiece Respirators with Viable H1N1 Influenza Aerosols

Abstract

OBJECTIVE. Specification of appropriate personal protective equipment for respiratory protection against influenza is somewhat controversial. In a clinical environment, N95 filtering facepiece respirators (FFRs) are often recommended for respiratory protection against infectious aerosols. This study evaluates the ability of N95 FFRs to capture viable H1N1 influenza aerosols. METHODs. Five N95 FFR models were challenged with aerosolized viable H1N1 influenza and inert polystyrene latex particles at continuous flow rates of 85 and 170 liters per minute. Virus was assayed using Madin-Darby canine kidney cells to determine the median tissue culture infective dose (TCID50). Aerosols were generated using a Collison nebulizer containing H1N1 influenza virus at 1 x 10(8) TCID50/mL. To determine filtration efficiency, viable sampling was performed upstream and downstream of the FFR. RESULTS. N95 FFRs filtered 0.8-μm particles of both H1N1 influenza and inert origins with more than 95% efficiency. With the exception of 1 model, no statistically significant difference in filtration performance was observed between influenza and inert particles of similar size. Although statistically significant differences were observed for 2 models when comparing the 2 flow rates, the differences have no significance to protection. CONCLUSIONS. This study empirically demonstrates that a National Institute for Occupational Safety and Health-approved N95 FFR captures viable H1N1 influenza aerosols as well as or better than its N95 rating, suggesting that a properly fitted FFR reduces inhalation exposure to airborne influenza virus. This study also provides evidence that filtration efficiency is based primarily on particle size rather than the nature of the particle's origin.

Assessment of a respiratory face mask for capturing air pollutants and pathogens including human influenza and rhinoviruses

“…The reduction of viable H1N1 influenza conferred by five brands of N95 face mask was found to range from 96.3% to 99.995% by Harnish et al (30). The nearly three log 10 reduction in penetration of viruses observed in the current study and in other studies using N95 face masks represents an improvement over the 2.8-fold reduction in penetration of genomic copies for influenza virus challenged via a fine (<5 μm) aerosol obtained during testing of a surgical mask (25).…”

“…Any increased benefits of N95 facepiece respirators such as the test mask over surgical masks are likely dependent upon the ergonomic fit of the mask to the wearer's face. This is because in the absence of a tight fit, inward leakage would be expected to dominate over filter penetration as the predominant mode of entry of particulates/aerosols containing infectious agents into the mask, regardless of the type of mask (30)(31)(32)41). A controlled clinical study failed, however, to reveal a significant difference in protection of healthcare workers using fit-tested vs. nonfit-tested N95 masks (42).…”

Validation and Application of Models to Predict Facemask Influenza Contamination in Healthcare Settings

“…The requirement to incorporate such technologies in future standards (for example, Project BREATHE's B95 standard) is being debated. Research has been conducted on facemasks with integrated antimicrobial technology, and the FDA has cleared a few antimicrobial FFRs . Research has also examined the efficacy of chemical and energetic methods to decontaminate FFRs.…”

“…Studies in various workplaces have demonstrated that fit‐tested FFRs, when used in a complete respiratory protection program, are effective at reducing inhalation exposures, whereas SMs are far less effective for this purpose because of their poorer fit and filtration performance . Laboratory studies have demonstrated the superior filter performance of FFRs over SMs by using various simulants for respiratory pathogens …”

Relative survival of Bacillus subtilis spores loaded on filtering facepiece respirators after five decontamination methods

“…Each had an effective diameter of 40 mm and a filtration area of 12.6 cm 2 . The sampling flow rate of the pump was 6.3 L/min, which produced the desired face velocity …”