Covid-19 may spread through short conversation: IISc study

Asymptomatic transmission, through activities like speaking, is believed to be an important and rapid route of Covid-19 spread across India as well as the world.

The spread of the disease through droplets carrying viral particles can occur when a person talks, coughs, or sneezes.

The fluid dynamics behind droplets causing infection involve their transmission in the air.

For example:

• The bigger the droplet, the more the viral load inside it, and the higher the chances of infecting people nearby.
• Bigger droplets tend to be in the air attached to any physical surface.
• Small droplets may evaporate or squeeze in size and become too light to be carried away to different points of contact.

(Fluid dynamics is the branch of applied science that is concerned with the movement of liquids and gases.)

Findings

The researchers found several things in their study, having used the height of two individuals to calculate the chances of infection.

The team visualised scenarios using speech jets in which two mask-less people are standing two, four, or six feet apart and talking to each other for about a minute, and then estimated the rate and extent of spread of the speech aerosols from one to another.

A speech jet is a narrow cone with a rapid stream of liquid or gas forced through a small nozzle under pressure.

Meanwhile, an aerosol is the suspension of particles dispersed in air or gas.

They found the following:

• A two-way conversation is shown to significantly reduce aerosol exposure compared with a relative monologue by one person and silence of the other.
• An unequal conversation is shown to significantly increase the infection risk for the person who talks less.
• A small height difference is worse for infection spread, due to reduced interference between the speech jets.

The study pertinently raises the point of the actual distance that must be followed during social distancing.

Results

The study yielded some significant results, said the researchers.

• The team computed the total exposure to aerosol on a listener due to speech flow from a speaker not only through inhalation but also through the mouth and eyes.
• In conversations, the active involvement of both people significantly lowers the aerosol exposure as compared to when one person is a passive listener.
• The lack of an equal speech pattern between two people reduces the jet interference and increases the risk of infection for the person who talks less.
• The risk of infection is reduced considerably during a “dialogue” as compared to a “monologue”, and a small height difference is found to be more dangerous than if the two speakers are of equal height.