Generation and sampling of nanoscale infectious viral aerosols

Abstract

Airborne viruses represent a potentially significant health threat. However, only recently have researchers begun to characterize the size and infectivity of viral bioaerosols in the nanoscale size range. There are limitations in the generation of test viral aerosols and the ability to sample with acceptable efficiency. Reported here is use of a laminar-flow water condensation method to efficiently sample nanoscale bioaerosols to sizes well below 100 nm. We used MS2 bacteriophage in water to provide an aerosol with particles sizes from 300 nm down to 45 nm for sampling by both an all-glass impinger (4 mm; AGI-4) and the water condensation bioaerosol sampler. We demonstrated the existence of infectious viral particles below 100 nm and a higher collection efficiency by the water condensation sampler compared to the AGI-4 at nanoscale sizes. For example, the water condensation bioaerosol sampler that collected particles at 45 nm in diameter had 20 times more infective virions per collected particle compared to the AGI-4. However, when we corrected the AGI-4 data for particle size-dependent collection efficiency, the results were similar. We also used quantitative reverse transcription polymerase chain reaction, along with culturing for infectivity to determine the percent infectivity of the aerosol by particle size. Finally, we used a simple calculation to determine that a large fraction of sub-100 nm particles did not contain infectious virus because of the low titer concentration of virus in the Collison fluid.

Collection of Viable Aerosolized Influenza Virus and Other Respiratory Viruses in a Student Health Care Center through Water-Based Condensation Growth

“…In previous studies, the VIVAS and similar devices were compared to the BioSampler for the collection of laboratory-generated virus-containing particles from below 100 nm to larger than 10 μm ( 20 , 21 ). In those study, the VIVAS outperformed the BioSampler for the collection of influenza virus and bacteriophage MS2 aerosols, due to gentle impaction and size amplification ( 20 , 22 ).…”

Collection, particle sizing and detection of airborne viruses

“…Finally, the 'collection efficiencies' reported in many virus aerosol studies are in reality 'relative collection efficiencies'; they are measures of the amount of virus collected by one sampler compared to that collected or calculated by a reference sampler. One reason for this gap in reporting is that a large percentage of the test virus is deactivated during aerosol generation or sampling processes (Zhen et al 2014;Walls et al 2016), and quantification of their inactivation rate proves challenging. The absolute efficiency of a virus sampler is very important for health risk assessments, because even if the tested sampler has high collection efficiency compared with some sampler considered to be state-of-the-art, it might still be possible that both samplers do not collect sufficient quantities of airborne viruses for accurate risk assessments.…”

“…Using gelatin filters, Zuo et al (2013) observed that the infectious virus distribution for MS2 phage aerosols in the size range of 100-500 nm was better represented by particle volume distribution rather than number distribution, although they offered no mechanistic explanation. Walls et al (2016) conducted laboratory studies on sampling size-selected MS2 aerosols (45, 90, 300 nm) with a water-based condensation sampler, and suggested that the number of infectious virions per particle was proportional to the cube of the particle diameter. Meanwhile, Pan et al (2019) found out that the composition of the nebulization suspension also affects the infectious count of viruses carried per particle, not always leading to volume size distribution.…”

Determination of the distribution of infectious viruses in aerosol particles using water-based condensational growth technology and a bacteriophage MS2 model

“…Compared with artificial saliva (AS) and bacterial cell culture medium (i.e., tryptic soy broth), human saliva seemed to be much less protective for bacteriophage MS2 (Zuo et al 2014). Using size-selective sampling of MS2 aerosols (45, 90, 300 nm) produced with DI water as the nebulization media, Walls et al (2016) found that the number of virions per particle depended on the carrier particle size, following a volume-based size distribution, and among the three sizes studied, the survivability of the MS2 was generally constant. Since these studies either used samplers that are inefficient in recovering infectious viruses or used limited size resolution to allow statistical analysis (Walls et al 2016;Zuo et al 2013), comprehensive studies that include sampling of a wide size range of particles with a reliable virus aerosol sampler will provide valuable information that will provide a better understanding of the infectivity of airborne viruses as a function of its carrier size and composition.…”