Explained: How far can singing/talking spread Covid?

Consonants release very large droplets — and B and P stand out as the biggest aerosol spreaders. At the same time, larger droplets fall to the ground earlier, and so have a shorter lifespan than smaller droplets. Is that a contradiction?

The act of singing emits particles into the air, and the novel coronavirus spreads through particles. So, what is the risk of Covid-19 spreading when a person sings — or talks? Two studies have examined the amount of particles emitted when singing and talking.

The broad findings

One paper, from Lund University in Sweden and published in Aerosol Research and Technology, found that:

* The louder you sing, the more particles you spread

* Consonants — particularly P, B, R, T — are bigger aerosol spreaders than vowels

The other paper, from the University of Bristol and awaiting peer review, found that:

* Singing does not produce very substantially more respiratory particles than speaking, when both are at a similar volume.

Vowels & consonants

The Swedish researchers measured particles emitted by 12 healthy singers and two people with confirmed Covid-19; 7 of the 14 were professional opera singers.

In a chamber with particle-free air, they sang a short Swedish song, Bibbis pippi Petter, repeated it 12 times in two minutes at constant pitch, then repeated it again with the consonants removed, leaving only the vowels.

“In our work we investigated a number of different aspects of singing: singing compared to talking, singing loud compared to normal singing, singing with face mask and singing consonants compared to vowels… We did not systematically compare all the different consonants, but noted that P, B, R and T generated a high numbers of droplets,” Jakob Löndahl, Associate Professor of Aerosol Technology at Lund University, said by email.

Size matters

Consonants release very large droplets — and B and P stand out as the biggest aerosol spreaders. At the same time, larger droplets fall to the ground earlier, and so have a shorter lifespan than smaller droplets. Is that a contradiction?

“I think this is still a topic of considerable scientific uncertainty,” Löndahl explained. “The main reasons for supposing a larger transmission of disease from the big droplets is that they can contain more virus than smaller aerosol particles, and that disease transmission usually occur at rather close contact and less over longer distances (however the reason for this could also be the dilution over longer distances).”

Absence of virus

As the two people with Covid-19 sang, the team measured the virus in the air close to them. The air samples contained no detectable amount of virus. “But the viral load can vary in different parts of the airways and between different people. Accordingly, aerosols from a person with Covid-19 may still entail a risk of infection when singing,” doctoral student Malin Alsved said in a statement.

Singing ‘Happy Birthday’

In the University of Bristol study, 25 professional performers were made to talk, and sing Happy Birthday in the “zero aerosol background” of an operating theatre. (Some reports have said it was the Lund University study that found singing Happy Birthday could spread the virus because of the consonants B and P, but Löndahl told The Indian Express that Happy Birthday was not sung in his team’s study.)

The University of Bristol researchers found is a rise in aerosol mass with increase in the loudness of the singing and speaking, rising by a factor of 20-30. However, singing does not produce very substantially more aerosol than speaking at a similar volume.

There were no significant differences in aerosol production between genders, or among different genres (choral, musical theatre, opera, choral, jazz, gospel, rock and pop).

Should performers sing?

The Lund University researchers suggested singing need not be silenced. A song can be sung with social distancing, good hygiene and good ventilation; masks can also make a difference.

The University of Bristol researchers noted that when the audience is large, singers may not be responsible for the greatest production of aerosol. Ways to ensure adequate ventilation may be more important than restricting a specific activity, they suggested.

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