First, there were concerns that the coronavirus could spread through the air. Now, there is a “substantial probability that normal speaking causes airborne virus transmission in confined environments”.
That’s the conclusion of research published in the Proceedings of the National Academy of Sciences (PNAS) in the US.
Talking launches thousands of tiny droplets that remain suspended in the air for up to 14 minutes, according to the The New York Times, which could explain “how people with mild or no symptoms may infect others in close quarters such as offices, nursing homes, cruise ships and other confined spaces”.
“Speech droplets generated by asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are increasingly considered to be a likely mode of disease transmission,” the PNAS study confirmed. “Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second.”
The US Centres for Disease Control and Prevention (CDC) urges Americans to wear masks in public to protect others from droplets exhaled by breath, speech coughs, and sneezes.
In mid-April, it was revealed that the “virus behind the world’s COVID-19 pandemic could stay infectious in the air for more than 12 hours”. It was found to be much more ‘resilient’ in the air than similar previous viruses SARS and MERS.
It was previously assumed that COVID-19 mostly spread through close contact, in large water droplets expelled from the nose or mouth when a patient coughed or sneezed.
These droplets could contaminate surfaces such as doorknobs, leading to an infection in those who touched the surface then their face. But the droplets were considered to be too heavy to survive long in the air.
However, it now appears some smaller droplets can remain in the air and be inhaled by others.
A cough can propel about 3000 respiratory droplets; sneezing as many as 40,000.
A study at the National Institute of Diabetes and Digestive and Kidney Diseases and the University of Pennsylvania showed that about 2600 small droplets per second were produced by talking.
The study found that speaking louder could generate larger droplets, in larger numbers. Researchers estimated one minute of loud speaking could produce 1000 virus-containing droplets.
“Based on this and other evidence, it would be wise to avoid extended face-to-face conversations with other people unless you are far apart and in a well-ventilated space, including outdoors,” Linsey Marr, a professor of civil and environmental engineering at Virginia Tech told The New York Times.
There is debate about how far the droplets can travel, with some scientists arguing they can be propelled more than 1.8 metres, depending on conditions such as the surrounding temperature, air currents and the force with which they are launched. One study suggests a slight breeze can transport the droplets more than five metres.
Researchers don’t yet know whether droplets from coughs, sneezes and speech are equally infectious, or how much of the virus is required to make someone sick by breathing it in.
Little wonder CNBC said the study had “huge ramifications for what kind of spaces and activities are considered safe” in the US, which has suffered close to 100,000 COVID-19 deaths. “Public transport and rooms with poor ventilation are considered high-risk areas for this kind of transmission.”
A CDC investigation of a cluster of COVID-19 infections in a church choir helped confirm that the disease could be transferred by more means than originally accepted.
“The act of singing, itself, might have contributed to transmission through emission of aerosols, which is affected by loudness of vocalisation,” the CDC report says.
“Following one meeting in early March that 61 people attended, there were soon 32 confirmed infections and another 20 secondary COVID-19 cases. Three people were hospitalised. Two died,” healthline.com reported.
The CDC’s official line now is that the virus spreads:
- between people who are within two metres of each other
- through respiratory droplets produced when a person with the infection coughs, sneezes, or talks
- when these droplets land in the mouth or nose of a person who is nearby.
“It may also be possible for a person to contract SARS-CoV-2 by touching a surface that has contaminated droplets on it, then touching their mouth, nose, or eyes.”
The World Health Organisation states that coronaviruses can remain active on certain surfaces for a few hours or several days, depending on variables such as the type of surface, temperature, and humidity.
Does the research suggest we should all be wearing face masks in public? Do you wear a face mask when you are out and about?
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