Myung-Heui Woo

Characterization of reaerosolization from impingers in an effort to improve airborne virus sampling.

Aims:  To assess the impact of reaerosolization from liquid impingement methods on airborne virus sampling.

Method for contamination of filtering facepiece respirators by deposition of MS2 viral aerosols

Abstract A droplet/aerosol loading chamber was designed to deliver uniform droplets/aerosols onto substrates. An ultrasonic nebulizer was used to produce virus-containing droplets from artificial saliva to emulate those from coughing and sneezing. The operating conditions were determined by adjusting various parameters to achieve loading density and uniformity requirements. The count median diameter and mass median diameter were 0.5–2 and 3–4μm, respectively, around the loading location when 35% relative humidity was applied. The average loading density was ∼2×103 plaque-forming units/cm2 for 5-min loading time with a virus titer of 107 plaque-forming units/mL. Six different filtering facepiece respirators from commercial sources were loaded to evaluate uniform distribution. For each of the six FFRs, the virus loading uniformity within a sample and across numerous samples was 19.21% and 12.20%, respectively. This system supports a standard method for loading viable bioaerosols onto specimen surfaces when different decontamination techniques are to be compared.

Effects of Relative Humidity and Spraying Medium on UV Decontamination of Filters Loaded with Viral Aerosols

ABSTRACT Although respirators and filters are designed to prevent the spread of pathogenic aerosols, a stockpile shortage is anticipated during the next flu pandemic. Contact transfer and reaerosolization of collected microbes from used respirators are also a concern. An option to address these potential problems is UV irradiation, which inactivates microbes by dimerizing thymine/uracil in nucleic acids. The objective of this study was to determine the effects of transmission mode and environmental conditions on decontamination efficiency by UV. In this study, filters were contaminated by different transmission pathways (droplet and aerosol) using three spraying media (deionized water [DI], beef extract [BE], and artificial saliva [AS]) under different humidity levels (30% [low relative humidity {LRH}], 60% [MRH], and 90% [HRH]). UV irradiation at constant intensity was applied for two time intervals at each relative humidity condition. The highest inactivation efficiency (IE), around 5.8 logs, was seen for DI aerosols containing MS2 on filters at LRH after applying a UV intensity of 1.0 mW/cm2 for 30 min. The IE of droplets containing MS2 was lower than that of aerosols containing MS2. Absorption of UV by high water content and shielding of viruses near the center of the aggregate are considered responsible for this trend. Across the different media, IEs in AS and in BE were much lower than in DI for both aerosol and droplet transmission, indicating that solids present in AS and BE exhibited a protective effect. For particles sprayed in a protective medium, RH is not a significant parameter.

Use of dialdehyde starch treated filters for protection against airborne viruses

Abstract In the event of a pandemic, the general public would use filters as protective devices. However, most commercial filters only remove airborne viruses physically without inactivating them, allowing reproduction on the surface and yielding the mask as a fomite. The objective of this study was to investigate the inactivation performance of dialdehyde starch (DAS) treated filters against airborne viruses. The viable removal efficiency by and relative survivability on the biocidal filters prepared with dialdehyde starch compared to untreated filters were investigated using MS2 bacteriophage at high relative humidity (80–90%) and room temperature. Experimental results showed no significant difference in viable removal efficiency and pressure drop between the treated and untreated filters for polypropylene filtering facepiece respirators. The pressure drop of DAS treated cellulose filters significantly decreased although there was no significant change in viable removal efficiency; the combination of these two factors resulted in an increase of filter quality. All biocidal filters showed a significantly lower relative survivability than untreated filters, and the relative survivability decreased as the concentration of DAS increased. The biocidal filter treated with 4% DAS presented an average of 30% survivability compared to the baseline of untreated filters. The results demonstrate that dialdehyde starch can be incorporated onto filters to provide an effective means for inactivating MS2 viruses through surface contact.