Reaerosolization of MS2 bacteriophage from an N95 filtering facepiece respirator by simulated coughing

Abstract

The supply of N95 filtering facepiece respirators (FFRs) may not be adequate to match demand during a pandemic outbreak. One possible strategy to maintain supplies in healthcare settings is to extend FFR use for multiple patient encounters; however, contaminated FFRs may serve as a source for the airborne transmission of virus particles. In this study, reaerosolization of virus particles from contaminated FFRs was examined using bacteriophage MS2 as a surrogate for airborne pathogenic viruses. MS2 was applied to FFRs as droplets or droplet nuclei. A simulated cough (370 l min(-1) peak flow) provided reverse airflow through the contaminated FFR. The number and size of the reaerosolized particles were measured using gelatin filters and an Andersen Cascade Impactor (ACI). Two droplet nuclei challenges produced higher percentages of reaerosolized particles (0.21 and 0.08%) than a droplet challenge (<0.0001%). Overall, the ACI-determined size distribution of the reaerosolized particles was larger than the characterized loading virus aerosol. This study demonstrates that only a small percentage of viable MS2 viruses was reaerosolized from FFRs by reverse airflow under the conditions evaluated, suggesting that the risks of exposure due to reaerosolization associated with extended use can be considered negligible for most respiratory viruses. However, risk assessments should be updated as new viruses emerge and better workplace exposure data becomes available.

Fig. 1.

Schematic of aerosol generating system.

Fig. 2.

Schematic of reaerosolization system.

Fig. 3.

Size distribution of loading (10⁴ p.f.u. cm⁻²) and reaerosolized droplet nuclei. ACI measured particle distribution over the range 0.65–7.0 μm. The black bars (n = 1) represent the loading aerosol size distribution and the gray bars (n = 5) represent the reaerosolized particle size distribution.

Fig. 4.

Microphotographs of the particle deposition on FFR layers. Top row, as-received FFR; middle row, droplet nuclei exposed FFR; and bottom row, droplet exposed FFR (left: outer layer and right: filter media layer). The scale bar is applicable to each image.