In many outbreaks caused by viruses, the transmission of the agents can occur through contaminated environmental surfaces. Because of the increasing incidence of viral infections, there is a need to evaluate novel engineering control methods for inactivation of viruses on surfaces. Ultraviolet germicidal irradiation (UVGI) is considered a promising method to inactivate viruses. This study evaluated UVGI effectiveness for viruses on the surface of gelatin-based medium in a UV exposure chamber. The effects of UV dose, viral nucleic acid type (single-stranded RNA, ssRNA; single-stranded DNA, ssDNA; double-stranded RNA, dsRNA; and double-stranded DNA, dsDNA), and relative humidity on the virus survival fraction were investigated. For 90% viral reduction, the UV dose was 1.32 to 3.20 mJ/cm2 for ssRNA, 2.50 to to 4.47 mJ/cm2 for ssDNA, 3.80 to 5.36 mJ/cm2 for dsRNA, and 7.70 to 8.13 mJ/cm2 for dsDNA. For all four tested viruses, the UV dose for 99% viral reduction was 2 times higher than those for 90% viral reduction. Viruses on a surface with single-stranded nucleic acid (ssRNA and ssDNA) were more susceptible to UV inactivation than viruses with double-stranded nucleic acid (dsRNA and dsDNA). For the same viral reduction, the UV dose at 85% relative humidity (RH) was higher than that at 55% RH. In summary, results showed that UVGI was an effective method for inactivation of viruses on surfaces.

Collection efficiencies of four bioaerosol samplers (Andersen impactor, AGI-30 impinger, gelatin filter, and nuclepore filter) were evaluated for virus-containing aerosols. Four different bacteriophages were used as surrogates for the mammalian viruses. Results showed that the collection efficiency was significantly affected by the morphology of the virus particles. For hydrophilic viruses, the collection efficiencies of the Andersen impactor, impinger, and gelatin filter were 10 times higher than that of the nuclepore filter. For hydrophilic viruses, the collection efficiencies of all four samplers were 10-100 times higher than hydrophobic viruses. The infectivity of the virus in collected samples was also evaluated for an AGI-30 impinger. Results showed that the viruses retained more infectivity when the samples were refrigerated (up to 1 day) during storage than when stored at room temperature (up to 8 h). Therefore, even when refrigerated, airborne virus samples collected using an impinger should be processed as soon as possible to avoid loss of virus infectivity. ᭧

The increasing incidence of infectious diseases has prompted the application of Ultraviolet Germicidal Irradiation (UVGI) for the inactivation of viruses. This study evaluates UVGI effectiveness for airborne viruses in a laboratory test chamber by determining the effect of UV dosage, different nucleic acid type of virus (single-stranded RNA, ssRNA; single-stranded DNA, ssDNA; double-stranded RNA, dsRNA; and double-stranded DNA, ds-DNA), and relative humidity on virus survival fraction after UVGI exposure.For airborne viruses, the UVGI dose for 90% inactivation was 339-423 µW sec/cm 2 for ssRNA, 444-494 µW sec/cm 2 for ssDNA, 662-863 µW sec/cm 2 for dsRNA, and 910-1196 µW sec/cm 2 for ds-DNA. For all four tested, the UVGI dose for 99% inactivation was 2 times higher than that for 90% inactivation. Airborne viruses with single-stranded nucleic acid (ssRNA and ssDNA) were more susceptible to UV inactivation than were those with double-stranded ones (dsRNA and dsDNA). For all tested viruses at the same inactivation, the UVGI dose at 85% RH was higher than that at 55% RH, possibly because water sorption onto a virus surface provides protection against UV-induced DNA or RNA damage at higher RH. In summary, UVGI was an effective method for inactivation of airborne virus.

Because of increasing incidence of virus-containing aerosols, ozone was potentially considered to be a promising method to inactivate airborne viruses. In this investigation, bacteriophages MS2, phi X174, phi 6, and T7 are under evaluation. The effects of ozone concentration, contact time, different capsid architecture of virus and relative humidity (RH) on inactivating airborne viruses by ozone were evaluated in a laboratory test chamber. It was observed that the survival fraction of airborne virus decreased exponentially with increasing ozone dose. Airborne viruses required ozone doses of 0.34 to 1.98 and 0.80 to 4.19 min-mg/m 3 for 90% and 99% inactivation, respectively. For all four tested, the ozone dose for 99% inactivation was 2 times higher than that for 90% inactivation. At airborne phase with a short contact time, viruses with more complex capsid architectures were observed to be less susceptible to ozone inactivation than those with simple ones. For all tested viruses at the same inactivation, the required ozone concentration at 85% RH was lower than that at 55% RH, possibly because the generation of more radicals from ozone reacting with water vapor at the higher RH. In summary, it was concluded that ozone is highly effective for the inactivation of airborne virus.

Because of increasing incidence of microorganism infections, there are concerns in engineering control of indoor microorganism for reducing airborne infectious diseases. Ultraviolet germicidal irradiation (UVGI) was considered to be promising to inactivate microorganisms. In this investigation, the in uences of UV dosage, microorganism species, and relative humidity on UVGI effectiveness were evaluated in a laboratory test chamber. A Collison nebulizer generated aerosols containing Escherichia coli, Bacillus subtilis spores, cells of Candida famata var. areri, and spores of Penicillium citrinum. The UVGI control effectiveness was determined as the ratio, NS=N 0 , where NS and N 0 were the colony concentrations collected by Andersen one-stage samplers at UVGI dosages of D and zero, respectively. In regard to 99% microorganism inactivation, the UVGI dosage ranges were 1017 to 2356 ¹W s/cm 2 , 15949 to 19345 ¹W s/cm 2 , 12917 to 17497 ¹W s/cm 2 , and 47984 to 89419 ¹W s/cm 2 for E. coli, B. subtilis, yeast, and P. citrinum, respectively. Signi cantly, the microorganism susceptibilities of E. coli were the highest and P. citrinum were the lowest. In regard to relative humidity effects, it was observed that the microorganism susceptibilities at 80% relative humidity were lower than those found at 50% relative humidity for all 4 types of the evaluated microorganisms.

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ABSTRACT. The in uences of physical factors, sampling time, and ow rates on total recovery rate of airborne bacteria were evaluated in a chamber by three sampling methods: AGI-30 all-glass impingers, Nuclepore ltration and elution method, and gelatin lters. The in uence of the biological factor, microorganism hardiness, was assessed by using sensitive Escherichia coli (E. coli) and hardy Bacillus subtilis (B. subtilis) spores. It was found that colony or relative survival of sensitive E. coli was much lower than those of hardy B. subtilis spores by the evaluated three sampling methods. Sampling ow rate did not have a signi cant in uence on the bacterial recovery by the three sampling methods. However, the relative survival of sensitive E. coli collected on Nuclepore and gelatin lters became lower as the sampling time increased because of dehydration effects. For hardy B. subtilis spores, it was demonstrated that recovery by gelatin lter was comparable to that by impinger. In conclusion, it was found that impingers could perform much better than ltration methods for sampling airborne bacterial bioaerosols.

ABSTRACT. The relationships between fungal aerosols and air pollutants r r r r r meteorological factors were investigated in the Taipei urban area. In summer, it ( ) was observed that geometric mean GM concentrations of airborne fungal aerosols were 2,835 CFU m I 3 and 2,651 CFU m I 3 at Kuting and Hsichih stations, respectively. In winter, GM levels of airborne fungi were 1,107 CFU m I 3 and 2,248 CFU m I 3 at Kuting and Hsichih stations, respectively. Moreover, fungal aerosol concentrations were observed to highly depend on weather conditions, and the highest concentration of total colony counts appeared when the temperature was 25-308 C, the RH was 60-70%, and the wind speed was -1 m s I 1 and from the S-SE wind direction. In addition, total fungal concentrations were negatively correlated with ozone concentrations, and concentration of Cladosporium spp. was positively correlated with hydrocarbons . PM were positively correlated with 10 Penicillium and the yeasts in Hsichih station. Our results demonstrated that airborne fungal aerosols are de nitely correlated with air pollutants and meteorological factors. The complex dynamic interactions were indicated to occur among bioaerosols, air pollutants, and meteorological factors.