Sampling efficiencies of two modified viable cascade impactors

Abstract

Prevention of airborne contagious diseases depends on successful characterization of aerosols in the environment. The use of cascade impactors to characterize ambient aerosols is one of the most commonly used methods, providing data on both particle size and concentration. In this study, the use of a cascade impactor recently described in the literature using 8 mL of liquid in Petri dishes (CI-L) was compared with a new method that uses wet membrane filters on top of wax filled Petri dishes (CI-WWMF). Sampling efficiencies of the cascade impactors were evaluated using 0.5, 1, 3, and 5 mm polystyrene latex (PSL) microspheres and aerosol consisting of single spores of Bacillus atrophaeus var. globigii (BG). The sampling efficiency of the CI-L was 6%, 11%, 17%, 21%, and 58% for 0.5, 1, 3, 5 mm PSL microspheres and BG spores, respectively. Higher overall sampling efficiencies of 71%, 91%, 60%, 64%, and 104% were observed for the same size and type of particles for the CI-WWMF. This study indicates that using wet filters on top of wax-filled Petri dishes (CI-WWMF) in a viable cascade impactor is more efficient than the CI-L method for size-selectively collecting biological aerosols from the environment. The CI-WWMF method is useful when a liquid medium is required for identifying and quantifying organisms using polymerase chain reaction (PCR) and immuno-assay techniques.

Comparison of three air samplers for the collection of four nebulized respiratory viruses ‐ Collection of respiratory viruses from air –

“…This may result in a shift of size fractionation, with larger particles being collected in lower stages and smaller particles escaping from collection by the cascade impactor. Furthermore, liquid spill‐over into other stages increases the chances of cross‐contamination and VTM can be spilled easily, making the transport of petri dishes challenging, as also reported by others 48,50 . The results of the present study show that the collection of infectious pH1N1 virus in agar was equally efficient as in semi‐solid gelatin and more efficient than in VTM, demonstrating that both, agar and semi‐solid gelatin but not VTM are suitable media for the collection of infectious pH1N1.…”

“…Furthermore, liquid spill‐over into other stages increases the chances of cross‐contamination and VTM can be spilled easily, making the transport of petri dishes challenging, as also reported by others. 48 , 50 The results of the present study show that the collection of infectious pH1N1 virus in agar was equally efficient as in semi‐solid gelatin and more efficient than in VTM, demonstrating that both, agar and semi‐solid gelatin but not VTM are suitable media for the collection of infectious pH1N1. In contrast, the opposite was true for HMPV, where collection of infectious virus was least efficient in agar, while it was comparably efficient in semi‐solid gelatin and VTM.…”

“… 20 , 47 , 48 , 49 However, the high flow velocities within the sampler push aside liquid medium where the air stream hits the surface, creating a dent, thereby increasing the jet‐to‐plate distance. 50 This may result in a shift of size fractionation, with larger particles being collected in lower stages and smaller particles escaping from collection by the cascade impactor. Furthermore, liquid spill‐over into other stages increases the chances of cross‐contamination and VTM can be spilled easily, making the transport of petri dishes challenging, as also reported by others.…”

“…Although the present study is the first to compare the use of solid, semi‐solid, and liquid media in the impactor in terms of viral collection efficiency, our findings that a semi‐solid collection surface works better than a pure solid or liquid one, are in agreement with the findings of other studies. For example, when Kesavan et al 50 compared the collection efficiency of the impactor with liquid and solid media as collection surface, efficiencies using liquid medium were considerably lower than those using wax‐filled petri dishes with wet membrane filters on top. In a study by Bekking et al, 48 high amounts of influenza virus RNA were collected from infected ferrets with the cascade impactor, however, attempts to recover infectious virus from air samples were unsuccessful.…”

Comparison of three air samplers for the collection of four nebulized respiratory viruses

“…Several other studies have also evaluated the collection efficiency of the BioSampler and cascade impactor, or have also employed electrostatic precipitation to collect microorganisms from air 42,[47][48][49] . However, experimental set-ups including nebulizer type, collection medium and the applied flow rate are not uniform among studies.…”