(Waqar Hussain, Lahore)

14/29-A Samanabad Lahore Pakistan ID No 35202-8963627-3 Cell No 03336700587
So far, scientists consider two ways of coronavirus transmission. One is infection coming from contact with some object, that has virus on it. The other one is by inhaling droplet emitted by sneezes and coughs of infected person. But some experts say that there is third infection route also. That is through micro-droplets that makes the spread somewhat akin to aerosol/airborne. It is alarming and demands some extra methods of protection.


There are new facts about infection mechanism of Coronavirus shown in NHK Documentary. Experts are looking at this new infection mechanism as the crucial step to prevent the further spread of the virus.

Kazuhiro Tateda, President The Japanese Association for Infectious Disease, says: “It seems transmission are happening during conversations and even when people are standing at a certain distance apart. These cases cannot be explained by ordinary droplet infection. We think infection comes from "micrometer particles". This transmission can be called "micro-droplet infection".

So how does, it takes place. In each case is conducting an experiment with the group of researchers. The team tracks particles in the air by using laser beam and then observing them by the high sensitivity camera. This technology allows to detect droplet as small as 0.1 micrometer (1/10,000 mm) wide. The experiment started, when a person was irritated to sneeze by rubbing inside nasal cavity with a straw. He sneezed, they saw large droplet of about 1mm diameter, that quickly fell on earth. Then looked through high sensitivity camera. They saw the small particles that seem to floating to the air. These particles are smaller than 10 micro meter or 1/100 of mm in diameter.

Then, they saw sneezing droplet from a different angle, the droplets were small and light and were drifting in the air. These are micro-droplets.

They came to know that sneezing was not the only source of these droplets. They ran the same experiment on a close range conversation, people generated a lot of micro-droplets when they talk loudly, the droplet between the two talking persons stayed where they were. They didn't drift away.

It is not yet known; what volume of micro-droplet leads to infection. But Tateda says; “We can’t rule out the possibility that micro-droplets have spread the virus to some extent”.

Tateda says: “Micro-droplet carry many viruses. We produce them, when we talk loudly or breathe heavily. People around us inhale them and that's how virus spread. We are beginning to see this risk now".

The risk of infection through micro-droplet becomes even greater in close space with poor ventilation.

The lab simulated the move of micro droplet in an air tight room, equal to the size of a classroom, the 10 people were in enclosed it. A person coughed once and spread about one hundred thousand droplets. Large droplet in simulation were shown in blue and green; most of these fell to the ground within 1 minute. But the micro-droplets shown in red continue to drift. In another simulation, which only showed micro-droplet, 5 minute later, 10 minute later, 20 minute later; the micro-droplets were still floating in space.

Masashi Yamakawak, Associate Professor, Kyoto Institute of Technology said: "If the air is not flowing, the micro-droplet won't move. And since they can't move on their own, they stay in place for some time”.

“But there is a way to prevent this stagnation of micro-droplets; by opening windows and increasing air circulation, it is believed to be effective. When you open a window, micro-droplets are quickly swept away. They are very small and light, so any air flow will get rid of them.” While Fateda says: “What's important is to create two openings. Do this at least once an hour. That lower the risk of infection considerably.”


Chines conducted a research on Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during recent COVID-19 Outbreak, as the transmission of COVID virus through human respiratory droplets and by contact with infected persons was clear, the aerosol transmission had been little studied.

The researchers took 35 aerosol samples of three different types; total suspended particle, size segregated and deposition aerosol) and were collected from Patient Areas and Medical Staff Areas of Renmin Hospital of Wuhan University (Renmin) and Wuchang Fangcang Field Hospital (Fangcang), and Public Areas in Wuhan, China. A robust droplet digital polymerase chain reaction (ddPCR) method was employed to quantitate the viral SARS-CoV-2 RNA genome and determine aerosol RNA concentration.

Results showed that the ICU and general patient rooms inside Renmin, patient hall inside Fangcang had low airborne COVID virus concentration but deposition samples inside ICU and air sample in Fangcang patient toilet tested positive. The airborne COVID virus in Fangcang Medical Staff Area had bimodal distribution with higher concentration than those in Renmin during the outbreak but turned negative after patient’s number reduced and rigorous sanitization implemented. Public Area had undetectable airborne COVID virus concentration but obviously increased with accumulation of crowd flow.

Researchers concluded that room ventilation, open space, proper use and disinfection of toilet can effectively limit aerosol transmission of COVID virus. Gathering of crowds with asymptomatic carriers is a potential source of airborne COVID virus. The virus aerosol deposition on protective apparel or floor surface and their subsequent resuspension is a potential transmission pathway and effective sanitization is critical in minimizing aerosol transmission of COVID virus.

Apart from this study, Chines have said: the droplets remain in air for 3 hours and some Chines scientists have suspected that 60% of infection spread through the air.


Researchers examined air and surface sample of three COVID patient A, B and C in Singapore. 26 samples were taken from patient room, ante room, and the bathroom. The sample of patient A and B were taken after cleaning, and found all were negative. For patient C, whose samples were collected before cleaning, they found positive result with 13(87%) of 15 room sites and 3 (60%) of 5 total sites testing positive result for virus. All air sample were negative.

These were all special isolation rooms with special kind of ventilation. The fact that air exhaust outlet tested positive suggests that small virus droplet was displaced and landed there.

But it is important to remember that all of these studies looked at viral RNA and viral particle. But we don’t know whether these viral particles were still viable and able to infect human. So how long will viral particle survive? After they fall on the surface or get suspended in the air, will they stay viable to infect human?

Researcher looked at this also. They suspended the virus in air and on various surfaces like copper, cardboard, stainless steel and plastic, and took samples at various time points; they then look to see whether that virus was still able to infect cases. They found SARS COV-2 was most stable on plastic up to 72 hours (3 days); followed by stainless steel with 48 hours (2 days); cardboard 24 hours (1 day) and copper 8 hours.

Areoles virus remain viable for the entire experiment when lasted three hours.

In the last statement of the paper, researchers say: if there is ongoing contradictory finding in multiple studies (as with the influenza virus), and Sars-Cov-2, it may be more likely that the various transmission routes may predominate in different settings, making the airborne route for that particular pathogen more of an opportunistic pathway, rather than the norm.

This mean that the airborne route is probably mainly relevant for certain situations and that would be the hospital, hospital staff room, hospital changing room as well as crowded and badly ventilated public spaces.

Everyone else is probably more likely to get the virus through touching surfaces and bad hand hygiene and then touching their face.

In summary, data suggest that concentration of suspended virus in the air increases form almost no virus in public places, ICU and isolation rooms. To a little more in crowded outdoors, even more in medical staff rooms, and patient toilets. A lot more in staff change rooms, where they take off their protective apparels.

In general, the concentration of virus in the air inside hospital seems to be low but may be significantly elevated when staff has spent long hours with patient so droplet/aerosol deposited on their protective gears. When they then take off protective equipment, the positive material might become re-suspended in the air.

Medical staff might have false sense of security when they are outside the patient rooms like in medical staff rooms or changing room. But the data suggest that these are places where most likely to be infected.

What the data also show is that patient toilet seem to be particularly prone to contamination and high clean measures seem to be necessary to prevent transmission.


The researchers of Aalto University, the Finnish Meteorological Institute, the state-owned technical and innovation centre VTT and Helsinki University conducted a research on COVID transmission route and found that coronavirus droplets ejected when a person coughs, sneezes or even speaks can remain suspended in the air for minutes rather than immediately sinking to ground. The droplet are extremely small aerosol particles and travel on air currents.

Differentiation between aerosol/airborne and droplet transmission:

Dr. Wong Sin Yew, infections disease specialist, differentiated aerosol/airborne transmission and droplet transmission in these words:

“In aerosol transmission, equivalent to term airborne transmission, usually the particle size is less than 10 micro meter. When you talk about droplet; particle size tends to be larger than 20 micro meters usually. If you have larger size, droplet travel lesser distance. Where for aerosol/airborne transmission, distance can be much farther. In airborne, just the breathing out, can transmit the virus. So aerosol/airborne can affect both near and long distance people. Whereas the droplet transmission is only 1 to 2-meter range.

Furthermore, aerosol/airborne is spread by coughing, sneezing, talking and exhaling. Whereas droplet transmission is confined to coughing and sneezing only”. People who inhale the airborne germs do not have to have face-to-face contact or be in the same room as the infected person. It can go across the room. Aerosol goes to person’s lung while droplet mostly reach trachea.

If a common science students look on above findings of Japanese Chines and Singaporean; one can guess that when droplets outburst, there are chances of range of various sizes; micro, medium and macro. Then there is also chance that some of medium size droplets to evaporate and become smaller, often called droplet nuclei.

So, keeping in mind, Japanese finding, Chinese studies, Singapore research, Finland report and Dr. Wong Sin Yew’s differentiation. It seems that COVID’s virus droplet of 10 micro meter can have some small sort of aerosol/airborne transmission. However, mostly it is droplet transmission.

Whether the finding of Japanese, Chinese, Singaporean, Finnish are accurate or not? Sagacity demands to give them due consideration for the time being, till the exact mode of spread is confirmed and it is of prime importance to adopt precautionary measurement for all three modes of transmissions.

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