Could COVID-19 be transmitted through droplets released while speaking?

A study published in the New England Journal of Medicine (NEJM) used laser light-scattering technology to investigate evidence of speech-generated droplets.

Myupchar April 16, 2020 15:42:53 IST
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Could COVID-19 be transmitted through droplets released while speaking?

"Is COVID-19 airborne?" This question has generated a lot of interest in academic circles, and the insights gained from these inquiries will have a profound impact on our response to the pandemic. 

According to the WHO’s latest guidelines, COVID-19 is spread by droplet transmission; a sneeze or a cough releases the virus that can be inhaled by people in the vicinity, or land on surfaces which other people touch and then transfer to their mucosal membranes. Airborne transmission is different. It involves droplets smaller than 5 micrometres in diameter (about the size of a red blood cell) that remain in the air for longer periods because of their minuscule size. Airborne transmission would mean that the virus can infect people at further distances and be transmitted even by just speaking. 

Could COVID19 be transmitted through droplets released while speaking

Representational image.
Image by Christo Anestev from Pixabay.

A study published in the New England Journal of Medicine (NEJM) used laser light-scattering technology to investigate evidence of speech-generated droplets.

What were the findings of the study?

The inside of a cardboard box was painted black, and a green laser was used to create a sheet of light on one end of the box. Volunteers spoke into the open end of the box, and the laser light exposed any droplets that reached it. Flashes were produced by the green laser as the droplets passed through which were recorded by an iPhone video camera that allowed the researchers to estimate their size.

The volunteers were asked to repeat the phrase ‘Stay Healthy’ with and without a mask. The findings confirmed that aerosols were generated - interestingly, louder speech produced more aerosols. On speaking softly, 227 droplets were registered, whereas 347 droplets were registered when speaking loudly.

Encouragingly, when volunteers donned masks and spoke, no droplets were registered. 

What is the significance of the findings?

The researchers didn’t test whether these droplets were sufficient to transmit the disease - that remains the crux of the debate. However, the findings do suggest that wearing a homemade mask would limit the transmission of droplets of various sizes; recommendations endorsed by the Ministry of Health and Family Welfare (MoFHW) as well. These findings also underline the merits of ventilating rooms by turning on fans and opening doors and windows and avoiding overcrowding in spaces.

A brief survey of evidence for airborne transmission

Previous studies have shown that 39% of people with influenza exhaled infectious aerosols. The WHO has also suggested that airborne transmission is possible when conducting medical procedures such as intubation and swab tests - which underlines the need for personal protective equipment (PPE) for health workers.

A study conducted in Nebraska generated much interest; researchers found viral RNA in around two-thirds of the air samples they collected from a hospital and quarantine facility housing COVID-19 patients. However, cell cultures didn’t find these viruses to be infectious. 

The fact is that there are several variables at play; to what extent do environmental factors determine airborne transmission? How much virus is required to infect a person?

These are complicated questions to answer, and it is unlikely we will know for certain soon. Given these gaps, scientists are urging extra caution and the donning of masks is becoming the norm as well. 

For more information, read our article on How does COVID-19 spread?

Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.

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