Short-range exposure to airborne virus transmission and current guidelines

Abstract

Significance Violent expiratory events like coughs and sneezes represent an important route for the spread of respiratory viruses, such as SARS-CoV-2, the virus responsible for COVID-19. We use finely resolved experiments and simulations to quantify how the turbulent cloud of moist air exhaled during a sneeze largely increases the airborne time and the lifespan of virus-loaded droplets. By providing visualizations of the spatial distribution of the virus copies, we highlight the high infection risk associated with droplets that remain airborne in the near proximity of an infected individual. The present study aims at raising awareness among public health authorities about this infection risk, which is grossly underestimated by current guidelines. After the Spanish flu pandemic, it was apparent that airborne transmission was crucial to spreading virus contagion, and research responded by producing several fundamental works like the experiments of Duguid [J. P. Duguid, J. Hyg. 44, 6 (1946)] and the model of Wells [W. F. Wells, Am. J. Hyg. 20, 611–618 (1934)]. These seminal works have been pillars of past and current guidelines published by health organizations. However, in about one century, understanding of turbulent aerosol transport by jets and plumes has enormously progressed, and it is now time to use this body of developed knowledge. In this work, we use detailed experiments and accurate computationally intensive numerical simulations of droplet-laden turbulent puffs emitted during sneezes in a wide range of environmental conditions. We consider the same emission—number of drops, drop size distribution, and initial velocity—and we change environmental parameters such as temperature and humidity, and we observe strong variation in droplets’ evaporation or condensation in accordance with their local temperature and humidity microenvironment. We assume that 3% of the initial droplet volume is made of nonvolatile matter. Our systematic analysis confirms that droplets’ lifetime is always about one order of magnitude larger compared to previous predictions, in some cases up to 200 times. Finally, we have been able to produce original virus exposure maps, which can be a useful instrument for health scientists and practitioners to calibrate new guidelines to prevent short-range airborne disease transmission.