How does the body of “super-carriers” spread the coronavirus? Scientists explain

The “super-carriers” infect much more than the others. Why is this happening? This can be influenced by behaviors such as speaking out loud. However, it turns out that some people emit more aerosols (which can potentially infect). Who could be the biggest “producer” of such molecules? Here’s what scientists have managed to find out.

1. Certain behaviors, including talking loudly, breathing quickly, or strenuously, appear to play a major role in spreading the disease
2. It also turns out that there are people who produce more of these aerosols. – There must be a physiological reason that causes people speaking with the same amplitude and tone to emit a very different number of particles – explains the expert
3. One explanation may be the viscosity of the fluid and the way it responds to deformation. People with a naturally higher viscosity fluid may produce more of these sprays
4. Particle research is hampered by the nature of the aerosols themselves, which are sensitive to environmental conditions, which may affect research results
5. For more up-to-date information on the coronavirus, please visit the TvoiLokony home page

Why are some people more contagious than others?

Before the SARS-CoV-2 pandemic, scientists had little interest in how we exhale potentially infectious aerosols. Most were interested in the reverse process – inhaling infected matter. The COVID-19 era has changed this approach, and scientists have focused on how our lungs “throw” infectious material into the air, i.e. tiny respiratory droplets (aerosols). Understanding this mechanism will help to understand why SARS-CoV-2 spreads so easily and what makes some people “superbearners”.

Coronavirus is easily transmitted from person to person mainly because the infection can be asymptomatic. In such a situation, a person infected with SARS-CoV-2 unknowingly spreads the pathogen around him, infecting others. However, not all are contagious in the same way.

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It is known that certain behaviors, including talking loudly, breathing quickly or strenuously, appear to play a major role in spreading the disease. It turns out, however, that there are people who simply produce more of these sprays. – They don’t have to sneeze or cough. They just breathe and talk, says Donald Milton, an aerosol transmission expert at the University of Maryland.

Determining who and why is the largest “producer” of potentially infectious aerosols is proving difficult. Many biological and physical factors that influence particle production are difficult to analyze and even measure. What did the scientists find out?

How do we produce aerosols?

An aerosol is any particle (wet or dry) that can be suspended in air for several minutes to hours. Our airways produce a wide range of aerosols – from tiny droplets just a few micrometers in diameter to droplets visible to the naked eye – the so-called respiratory droplets.

From the point of view of pathogen transmission, the smallest aerosols are of particular importance. Compared to larger particles, they stay in the air much longer and travel longer distances. Tiny aerosols are formed in the “deeper” part of the respiratory tract – in the bronchioles (they have the form of very fine tubes, located between the bronchi and alveoli). The largest droplets are formed in the mouth, escaping with saliva during a conversation (which you can often even feel). Aerosols also escape through the nose, but the main “escape” route for them is our mouth.

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While the general mechanics of creating respiratory aerosols is the same for everyone, there are large variations in the amount of particles sprayed. To find out about it, just take a look at people breathing at the bus stop on a cold day. The exhaled vapor cloud will be greater for some, and less for others.

As Lidia Morawska, a physicist from Queensland University of Technology emphasizes, this phenomenon should not come as a surprise, taking into account the complexity of the respiratory tract. Explaining why, he gives an example of a solid mist from a perfume bottle: “Unlike a perfume bottle, which has only one tube, there are many different airways in the airways – with different widths and lengths,” he explains. And while it is difficult to quantify this complexity even for just one person, scientists know which people make more of these aerosols.

Why do people emit different numbers of aerosols?

In a 2019 study, William Ristenpart, a disease transmission chemist at the University of California, Davis, and his team found that the louder someone talks, the more aerosols they emit. It also found that some of the participants in the experiment produced more aerosols than others – even when they spoke equally loudly. – Apparently, there must be some physiological reason that causes people speaking with the same amplitude and the same tone to emit a very different number of particles – says Ing. Ristenpart. Such persons were called “superemitters”.

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One possibility, in his opinion, is the viscosity of the fluid and the way it responds to deformation. Earlier studies have found that inhaling salt water mist, which is less viscous than mucus-filled breathing fluid, causes people to produce fewer aerosol particles. On the other hand, people with a naturally higher viscosity fluid may produce more of these aerosols.

To complicate matters, a respiratory infection can cause changes in the respiratory fluids. The density of the fluid increases, for example, during bronchial infections, influenza or in chronic conditions such as asthma or cystic fibrosis.

Difficult research. “Even now, the way flu spreads are controversial”

Unfortunately, particle research is hampered by the nature of the aerosols themselves. They are sensitive to environmental conditions – temperature, air flow, humidity, and this can influence the test results. These factors have hampered research into aerosol transmission for decades. Even now, in 2020, the way flu spreads is controversial, says Ristenpart, who recently published a study showing that flu viruses can bind to dust particles.

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Currently, in the era of the SARS-CoV-2 pandemic, aerosol research is in the center of attention. Many experts now agree that better indoor ventilation and the use of protective masks can help reduce the spread of COVID-19.

A few months ago, Lidia Morawska and many other aerosol scientists called for a greater focus on the transmission of SARS-CoV-2 by airborne aerosols. Moreover, it is necessary to conduct systematic research on this area.

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Looking back, it turns out that while the growing interest in aerosol testing increases during epidemics of respiratory diseases, such as SARS or the H1N1 influenza virus, this attention disappears after the crisis is overcome. “If we approach the problem so short-sighted, as policy makers and sponsors contribute, the solutions we find will always be temporary,” warns Lydia Bourouiba, a fluid dynamics scientist at the Massachusetts Institute of Technology.

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