British researchers are now studying how long the coronavirus can survive in the air, writes The Guardian.
The researchers will test how long the virus remains contagious under different climatic conditions, and will try to answer a very essential question:
How long can the coronavirus SARS-CoV-2 survive in the small aerosol particles we exhale?
In a high-security laboratory near Bristol, researchers can now be only weeks away from finding out, writes The Guardian.
And they have developed a brand new machine that they believe will be suitable for the task, described in a study in the Journal of The Royal Society Interface in January 2019.
– Important question
On Monday, they begin introducing droplets of live Sars-CoV-2 and lifting them between two electrical rings to test how long the virus remains contagious under various environmental conditions.
– This is a very important question, says Professor Denis Doorly at Imperial College London to the British newspaper and adds:
– There is now great interest in what it takes to reduce the risk of infection in closed rooms. It all depends on knowing how viable the virus remains in the air, says Doorly, who himself is not involved in the research.
Until now, it has been expected that covid-19 is mainly continued through droplet infection, through respiratory droplets that are produced when an infected person coughs, sneezes, sings, talks or breathes.
These drops fall quickly to the ground, and represent the very logic behind the 2-meter rule.
At the same time, there is a growing consensus among experts that the virus can occur in smaller droplets called aerosols, which can be carried over greater distances by air currents and accumulate in poorly ventilated rooms.
This suspicion is largely based on outbreaks in restaurants and choirs, where people have been infected despite being at a certain distance from the carrier.
Genetic material from the virus has also been detected in air samples from poorly ventilated rooms, such as hospital toilets, but no one has yet identified live infectious viruses in air samples, says Professor Jonathan Reid at Bristol University, who is leading the new research.
“We know that when bacteria or viruses become airborne in airway droplets, they dry in very quickly and can lose viability, so it is important to understand when considering the role of airborne transmission in covid-19 transmission,” says Reid.
According to The Guardian, researchers have been using sealed vessels, so-called Goldberg drums, for decades to investigate how long viruses can survive in aerosol droplets.
The virus is injected into the drum, which rotates to keep the droplets airborne, and samples are taken periodically to check for live viruses.
Using this method, US researchers have estimated that Sars-CoV-2 has an aerosol half-life of 1.1-1.2 hours – meaning that half of the particles are out of the air after this time – and infectious virus could still be detected after three hours, when the experiment ended.
However, these calculations are imprecise due to the time it takes to inject the virus into the drum and the large amount of fluid used, which does not reflect exactly what happens when we cough or breathe.
Bristol researchers have therefore developed devices that allow them to generate any number of small, virus-containing particles – invisible to the naked eye – that float gently between two electrical rings for anywhere from seconds, to hours, to days.
The ambient air temperature, humidity and UV light intensity are tightly controlled and can be manipulated to recreate various real-world scenarios.
“We can effectively mimic a cold, wet British winter or, even, a hot, dry summer in Saudi Arabia, to see how these dramatic differences in environmental conditions affect how long the virus remains contagious while in the air,” he said. Allen Haddrell, the chemist at the University of Bristol who designed and built the device, called the Celebs, using 3D printers.
The team receives funding from UK Research and Innovation and the National Institute for Healthcare Research.
The US government has expressed its interest in the technology, to study other pathogens.
Until now, the team has practiced hovering aerosols that contain a mouse coronavirus, which is harmless to humans.
Here they have seen a large drop in infectivity during the first 10 minutes after the virus was released.
– We have also seen that this mouse virus at 10 degrees survives much longer than at warmer temperatures, Haddrell says.
On Monday, the researchers will let the coronavirus SARS-CoV-2 soar for the first time, which means that they can have the first results by the end of the week.
– These will be made available to decision-makers and sent for peer review in scientific journals, says Reid.
– Interesting and important
The National Institute of Public Health (NIPH) believes the research has something to offer.
– This is interesting and important research. The big question, which has proved difficult to clarify, is to what extent such airborne infection has practical significance. There is quite broad agreement that the most important mode of transmission is droplet transmission through air over shorter distances, says director Atle Fretheim in FHI and adds:
“Even if you can find some live viruses that have moved in the air over longer distances, it does not automatically mean that it involves a significant risk of infection,” says Fretheim.
Espen Rostrup Nakstad in the Norwegian Directorate of Health is open to the fact that airborne infections can play a role in the spread of infection.
– When people sneeze, cough, shout or use a loud voice, small drops are spread with the air from the mouth and nose. These drops can contain infectious viruses and bacteria when we have respiratory infections, says the assistant health director to Dagbladet.
For most respiratory viruses, including SARS-CoV-2, large droplets will be most contagious because they carry the most virus particles. They also fall to the ground fastest due to gravity, and therefore do not spread so easily over greater distances than 1-2 meters.
– Small droplets, so-called aerosols, can, however, stay longer in the air before they reach the ground, and for the most contagious respiratory viruses that exist, you can actually be infected by entering a completely empty room where a sick person has just stayed , points out Nakstad.
– Can be spread via airborne infection
He adds that for SARS-CoV-2 we do not yet know how easy it is to become infected with aerosols.
– It depends on how long the virus “survives” in small drops before it dries out, and not least on how many virus particles you have to be exposed to before you become infected. The research that is available today indicates that SARS-CoV-2 can be spread via aerosols, ie airborne infections, but that droplet infection through close contact with sick people is the most common cause of infection, says Nakstad and elaborates:
– Airborne infections through aerosols may possibly explain why so many people claim to have been infected by asymptomatic people who do not cough and sneeze or feel sick. This is being mapped in ongoing studies.
Nakstad points out that the uncertainty associated with airborne infection is also the reason why hospitals use extra protection in so-called “aerosol-generating procedures”, which provoke coughing and sneezing from infectious patients who are close to health personnel.
– In most other patient situations, it has been shown that ordinary surgical face masks protect well, and this supports the assumption that covid-19 is primarily transmitted through normal contact and droplet infection. If you also follow normal infection control routines and keep your distance from sick people, you are in any case very well protected against infection, says Nakstad.