Using soft aerosolization and sampling techniques for the conservation of virus infectivity during airborne exposure experiments

Recurrent epidemic outbreaks such as the seasonal flu and the ongoing COVID-19 are disastrous events to our societies both in terms of fatalities, social and educational structures, and financial losses. The difficulty to control their spread and minimize their consequences is a first evidence that basic mechanisms of transmission for such pathogens is still poorly understood. Three different routes of virus transmission are known: direct contact (e.g. through handshakes) and indirect contact through fomites; ballistic droplets produced by speaking, sneezing or coughing; and airborne transmission through aerosols which can also be produced by normal breathing. The latter route, which has long been ignored, even by the World Health Organization during the COVID-19 pandemics, now appears to play a significant role in the spread of airborne diseases (e.g. Chen et al., 2020). Further scientific research thus needs to be conducted to better understand the mechanistic processes that lead to airborne virus inactivation as well as the environmental conditions favourable to these processes. In addition to modelling and epidemiological studies, chamber experiments, where viruses are exposed to various types of humidity, temperature and/or UV dose, offer to simulate everyday life conditions for virus transmission. However, the current standard instrumental solutions for virus aerosolization to the chamber and sampling from it use high fluid forces and recirculation which can be highly damaging to the biological material (Alsved et al., 2020) and also do not represent the most relevant production of airborne aerosol in the respiratory tract. In this study, we utilized two of the softest aerosolization and sampling techniques: the sparging liquid aerosol generator (SLAG, CH Technologies Inc., Westwood, NJ, USA), which forms aerosol from a liquid suspension by bubble bursting, thus mimicking natural aerosol formation in wet environments (e.g. the respiratory system but also lakes, sea, toilets, etc…); and the viable virus aerosol sampler (BioSpot-VIVAS, Aerosol Devices Inc., Fort Collins, CO, USA), which uses condensational growth to gently collect particles down to a few nanometres in size. We characterize these systems with particle sizers and biological analysers using non-pathogenic viruses such as phages suspended in surrogate lung fluid and artificial saliva. We compare the size distribution of produced aerosol from these suspensions against similar distributions generated with standard nebulizers, and assess the ability of these devices to produce aerosol that much more resembles that produced in human exhaled air. We also assess the conservation of viral infectivity with the VIVAS vs. conventional biosamplers. Figure 1. Schemes showing the principle of operation of a) the sparging liquid aerosol generator (SLAG; extracted from Alsved et al., 2020) and b) the viable virus aerosol sampler (BioSpot-VIVAS; extracted from chtechusa.com). Acknowledgment We acknowledge the IVEA project in the framework of SINERGIA grant (Swiss National Science Foundation) References Alsved, M., Bourouiba, L., Duchaine, C., Löndahl, J., Marr, L. C., Parker, S. T., Prussin, A. J., and Thomas, R. J. (2020): Natural sources and experimental generation of bioaerosols: Challenges and perspectives, Aerosol Science and Technology, 54, 547–571. Chen, W., Zhang, N., Wei, J., Yen, H.-L., and Li, Y. (2020): Short-range airborne route dominates exposure of respiratory infection during close contact, Building and Environment, 176, 106859.