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How Does COVID Spread During Short Conversations?

On Monday, India reported 12,781 new cases of Covid-19 and 18 deaths. There are 76,700 active cases in the country, and the daily positivity rate has increased by over 4 per cent. India has tallied 4,33,09,473 cases and 5,24,873 deaths [1].

Union Health Minister Mansukh Mandaviya stated on Monday that the ongoing trajectory of Covid-19 is encouraging and that the pandemic is nearing its end. During his presentation in Indonesia, he emphasised the importance of mutual recognition of COVID-19 vaccines, digital health systems that provide data interoperability, and strengthening research and manufacturing capabilities to eliminate inequalities [2].

Researchers from the Department of Aerospace Engineering at the Bengaluru-based Indian Institute of Science (IISc), collaborators from the Nordic Institute for Theoretical Physics in Stockholm and the International Centre for Theoretical Sciences in Bengaluru, have studied how and whether COVID spreads through short conversations. Results showed that the risk of getting infected was higher when one person acted as a passive listener than when they engaged in a two-way conversation [3].

How Does COVID Spread During Short Conversations?

One of the main ways COVID-19 spreads is via respiratory droplets, which are tiny particles released by infected individuals as they cough, sneeze, talk, sing, and even breathe. The connection between coughing and sneezing was obvious (people who are ill will cough and sneeze) to researchers. Still, speaking and singing seemed less suspicious at the time, until May 2020, when it was elevated to the forefront of a CDC report [3][4].

Now researchers from Bangalore, India, had found that the risk of becoming infected was higher when a person acted as a passive listener rather than when they engaged in a two-way conversation.

The study was based on the following questions:

"When a person sneezes or coughs, they can potentially transmit droplets carrying viruses like SARS-CoV-2 to others in their vicinity. Does talking to an infected person also carry an increased risk of infection? How do speech droplets or "aerosols" move in the air space between the people interacting?"

Here are the study findings:

  • An analysis of the movement of speech aerosols was conducted by the research team using computer simulations.
  • Using visual simulations in which two maskless individuals stand two, four or six feet apart and converse in a maskless manner for about a minute, the team estimated the rate and extent of the spread of speech aerosols from one person to another. The simulations showed that the risk of getting infected was greater when one person acted as a passive listener and did not participate in a two-way conversation.
  • There is also evidence that factors such as the difference in height between people talking and the amount of aerosol released from their mouths play an important role in viral transmission.
  • To analyse speech flows, they modified a computer program they developed to study cumulus clouds, typically seen on sunny days as fluffy cotton clouds.
  • As part of the analysis performed by the team on speech flows, the possibility of viral entry through the eyes and mouth was taken into account in determining the risk of infection. In contrast, most previous studies considered the nose as an entry point.
  • During the simulation, when the speakers were of the same height or drastically different heights (one tall and the other short), the risk of infection was much lower than when the height difference was moderate - the variation resembled a bell curve.
  • The team's findings suggest that merely turning their heads away nine degrees from each other while maintaining eye contact can significantly reduce the risk for the speakers.
  • In the future, the team intends to examine the effects of loudness differences and ventilation sources on viral transmission by simulating differences in the speaker's voices and the presence of ventilation sources in close proximity to the speakers.
  • Additionally, they plan to discuss with public health policymakers and epidemiologists to develop suitable guidelines.

"Speaking is a complex activity ... and when people speak, they're not really conscious of whether this can constitute a means of virus transmission," says Sourabh Diwan, Assistant Professor in the Department of Aerospace Engineering and one of the corresponding authors.

"Whatever precautions we can take while we come back to normalcy in our daily interactions with other people would go a long way in minimising the spread of infection," Diwan added [5].

On A Final Note...

COVID-19 virus particles can be transmitted through coughing, sneezing, breathing or speech, but speaking is one of the most effective ways [6]. Considering that COVID-19 transmission may occur even when people are asymptomatic or pre-symptomatic, evidence of symptoms should not be used as a basis for wearing a mask or determining whether or not to take other precautions, such as eating outdoors.

Wear a mask, wash your hands and always sanitise!

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