Effects of relative humidity and nebulized medium on UV decontamination of aerosolized viruses loaded on a filter

MYUNG-HEUI WOO(1), Tamara Smith(1), Adam Grippin(1), Diandra Anwar(1), Chang-Yu Wu(1)

(1) University of Florida, Gainesville

     Abstract Number: 792
     Last modified: May 14, 2010

Abstract
Increasing emphasis on bioterrorism and the spread of airborne pathogens have increased the public’s concern about respiratory protection. Although respirators and filters are designed to prevent the spread of pathogenic aerosols, a stockpile shortage is anticipated during the next flu epidemic, and reaerosolization of collected microbes is also possible. To address these potential problems, various decontamination technologies have been developed. Among them, ultraviolet-C (UV-C), which inactivates microbes by damaging thymine, is normally used in healthcare facilities. However, most studies of UV-C disinfection have focused on only intensity and exposure time without considering environmental parameters such as RH, nebulized medium and transmission mode, which affect viability of bioaerosols. The objective of this study is to assess the effects of these parameters on decontamination efficiency.
In our experiments we contaminate filters by different transmission pathways (droplet and aerosol) using three spraying media (de-ionized water (DI), beef extract (BE)) and artificial saliva (AS). Then we apply UV irradiation at constant intensity for different time intervals at one of three relative humidity conditions (30% (LRH), 60% (MRH) and 90% (HRH)).
The highest inactivation efficiency—around 5.8 on a log scale—was seen for DI aerosols containing MS2 on filters at LRH after applying UV intensity of 1.0 mW/cm2 for 30 mins. Inactivation efficiency of droplets containing MS2 was lower than that for aerosols containing MS2. High water content that absorbs UV and shielding of viruses by aggregate might be responsible for this difference. Across the different media, inactivation efficiencies in AS and in BE were much lower than in DI for both aerosol and droplet transmissions. The reason for this observation is likely due to the protective effect from solids present in AS and BE. Ongoing experiments at different RHs and differing droplet sizes will be reported in the conference.