Speech can produce jet-like transport relevant to asymptomatic spreading of virus

Abstract

Many scientific reports document that asymptomatic and presymptomatic individuals contribute to the spread of COVID-19, probably during conversations in social interactions. Droplet emission occurs during speech, yet few studies document the flow to provide the transport mechanism. This lack of understanding prevents informed public health guidance for risk reduction and mitigation strategies, e.g., the “6-foot rule.” Here we analyze flows during breathing and speaking, including phonetic features, using orders-of-magnitude estimates, numerical simulations, and laboratory experiments. We document the spatiotemporal structure of the expelled airflow. Phonetic characteristics of plosive sounds like “P” lead to enhanced directed transport, including jet-like flows that entrain the surrounding air. We highlight three distinct temporal scaling laws for the transport distance of exhaled material including 1) transport over a short distance (<0.5 m) in a fraction of a second, with large angular variations due to the complexity of speech; 2) a longer distance, ∼1 m, where directed transport is driven by individual vortical puffs corresponding to plosive sounds; and 3) a distance out to about 2 m, or even farther, where sequential plosives in a sentence, corresponding effectively to a train of puffs, create conical, jet-like flows. The latter dictates the long-time transport in a conversation. We believe that this work will inform thinking about the role of ventilation, aerosol transport in disease transmission for humans and other animals, and yield a better understanding of linguistic aerodynamics, i.e., aerophonetics.

Modes of Transmission of Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) and Factors Influencing on the Airborne Transmission: A Review

“…In addition, Holland et al reported that, similar to influenza, mumps, Haemophilus influenzae , whooping cough, and rubella, coronaviruses are transmitted by bioaerosol droplets [ 24 ]. Furthermore, Abkarian et al and Chong et al described how flows generated during speaking, singing, breathing, and laughing by asymptomatic and presymptomatic humans contribute to the spread of SARS-CoV-2 virus [ 4 , 5 ]. In addition, experiments and simulations were performed to quantify how exhaled air is transferred during talking and stressed that phonetic characteristics add complexity to the airflow dynamics, i.e., plosive sounds, such as certain words starting with the letter “P” in English, create intense vortical structures that act as “puffs” and quickly reach 1 m distances [ 4 ].…”

“…Furthermore, Abkarian et al and Chong et al described how flows generated during speaking, singing, breathing, and laughing by asymptomatic and presymptomatic humans contribute to the spread of SARS-CoV-2 virus [ 4 , 5 ]. In addition, experiments and simulations were performed to quantify how exhaled air is transferred during talking and stressed that phonetic characteristics add complexity to the airflow dynamics, i.e., plosive sounds, such as certain words starting with the letter “P” in English, create intense vortical structures that act as “puffs” and quickly reach 1 m distances [ 4 ]. Moreover, speech corresponding to a train of such puffs can make a conical, turbulent, jet-like flow and generate directed transport more than 2 m away in 30 s of conversation [ 4 ].…”

“…The rapid outbreak of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that is spread via airborne, droplet, contact, and fecal–oral transmission modes constitutes a worldwide and disruptive challenge to societies [ 1 , 2 ]. Both symptomatic and asymptomatic carriers have been recognized to transmit the SARS-CoV-2 virus via various modes of transmission [ 3 , 4 , 5 ], causing severe respiratory infections among patients receiving medical care in hospitals [ 6 , 7 , 8 , 9 , 10 , 11 ]. Hence, the COVID-19 outbreak has been declared a global public health emergency of international concern by the World Health Organization (WHO) [ 12 , 13 , 14 ].…”

Modelling uncertainty in the relative risk of exposure to the SARS-CoV-2 virus by airborne aerosol transmission in well mixed indoor air

“…Several studies have explored this using idealised models, suggesting that the concentration of aerosols at 1.5–2 m from an infectious source is determined by the room ventilation. At a distance of m the concentration is determined by the exhaled plume and may be much higher [62] , [63] . This risk should particularly be considered in spaces with a high occupancy density where it is difficult to maintain distance, or where the nature of the activity means that it is essential to have closer contact.…”

Long-term, continuous, and multimodal monitoring of respiratory digital biomarkers via wireless epidermal mechano-acoustic sensing in clinical and home settings for COVID-19 patients

“…4k and l). Particularly, this ballistic behavior of droplets is a result of enhanced jet-like transport of the expelled airflow induced by the plosive sound 46 Figure 6i shows the coughing frequency versus the average coughing intensity for all hourly measurements, clustered into four demographic groups (males with age < 55, males with age ≥ 55, females with age < 55, females with age ≥ 55). The available results suggest that females tend to cough more than males.…”