CHENNAI: As the number of fresh COVID-19 cases surge daily, an increasing number of people have been concerned about whether the virus is airborne.
After a long global debate, the World Health Organisation (WHO), earlier this month acknowledged the possibility that the novel coronavirus can be spread through short-range aerosol transmission. It has created panic among the public. But what does this mean?
This simply means that under certain circumstances, the virus can be spread through air.
Dr Anantha Subramanian, a consultant pulmonologist, Kauvery Hospital, who has been treating COVID patients said that he strongly suspects that some of his patients contracted the disease through airborne transmissions.
"Droplet transmission is the most common source of the virus. But in some patients, that logic does not work. It seems like they took all precautions to prevent droplet transmission; especially the frontline workers (who got infected)," he said.
Kumaran (name changed), a senior doctor working at a government hospital in the city, on condition of anonymity, said airborne transmission is the only explanation why some frontline workers wearing protective equipment still ended up contracting the disease.
He said the chance of the virus becoming airborne is much higher in severely ill patients.
"The release of viral-loaded aerosols is very common when a patient is either put on or weaned off a ventilator. Coughs that come after high-pressure formation in the lungs also lead to production of aerosols," he said.
Referring to several recent studies across the world, the WHO has said that some outbreaks that have occurred in crowded indoor spaces suggest "the possibility of aerosol transmission." Such situations have arisen "during choir practice, in restaurants or in fitness classes," it said.
The organisation however added the caveat that the spread is although "combined with droplet transmission". Ultimately what people are concerned about is which air is safe to breathe and which is not.
Droplet and aerosol transmission:
One can visualise the difference between a droplet and aerosol is by seeing droplets as big drops and aerosols as small drops.
In the first case, droplets coming from a sick person's mouth or nose are heavy, and fall to the ground before they can get much further than six feet. This explains why the government has been insisting on people maintaining over 1.5 metres distance between each other. Aerosols, which are much smaller, can travel longer before landing.
Sivarama Krishnan, an assistant professor of Physics at the Indian Institute of Technology, Madras told The New Indian Express that aerosols can be imagined to be somewhat like a drunk person walking in a poorly-lit street at night.
"He takes incoherent steps, often back and forth, before finally converging slowly to a seat or a lamp-post. The smaller the particle the more intoxicated it is and more stochastic (unpredictable) its travel," he explained.
In a poorly ventilated room - a room where the flow is stagnant, small aerosol particles can circulate the room until they find their 'lamp-post', said Krishnan. The smallest droplets and particles (diameter < 5 μm–10 μm) may remain suspended in the air indefinitely, until they are carried away by a light breeze or ventilation airflow. This could be a wall, furniture or a person's body thus successfully infecting people. The lifetime of a virus that falls on a surface could be anywhere between a few minutes to a few hours.
A recent study published in the journal Nature about two hospitals in Wuhan, it was found that the most infected area was a 1 meter-squared mobile toilet in the patient area. Dr P Kuganantham, senior epidemiologist and Member of the State Special Task Force against COVID-19 says that he has suspected several cases of airborne transmission.
"The risk is the highest in air-conditioned rooms, particularly cabins or cage-like rooms. Which is why I am strongly against the idea of opening malls or cinema theatres. One asymptomatic person with COVID-19 is enough to infect all persons in an airconditioned room," he said.
Open the windows and wear your masks
Spacious well-ventilated rooms, on the other hand, bear a lesser risk of transmission. This means that an outdoor vegetable market is safer than a supermarket and a supermarket is safer than a small departmental store; this assumes that people maintain physical distancing norms though. So if you are indoors, open the windows to ensure maximum ventilation.