Coronavirus: the mystery of “silent carriers” without symptoms


Illustration: man on train

As the coronavirus spreads around the world, scientists are increasingly learning about its strange and dangerous behavior. Many patients had a cough, lost their sense of taste and smell, fever, while others did not show the disease, and they did not even guess that they were carriers of Covid-19.

Researchers say it is important to understand how many people are asymptomatic and whether the pandemic is being fueled by so-called “silent spreaders.”

When parishioners gathered in a church in Singapore on January 19, no one could have imagined that it would have global consequences for the spread of the coronavirus.

The Sunday sermon was traditionally read in Mandarin Chinese. Among those present was a couple who arrived from China in the morning.

The guests looked perfectly healthy, and no one could have imagined that they were carriers of the infection. At that time, it was believed that the obligatory symptom of coronavirus was a persistent cough, and that this is how the infection is transmitted.

No symptoms – no infection, it was believed then.

The Chinese soon left the church, but very quickly things got boring. Already on January 22, the woman fell ill, and her husband died two days later. This did not surprise anyone, because they arrived from the city of Wuhan – the epicenter of the coronavirus.

However, the following week, for no apparent reason, three Singaporeans fell ill – the first, at that time the most mysterious, cases of infection in the country. An investigation into the causes of their illness has helped uncover new and very disturbing details of how the coronavirus has so successfully found new victims.

“Virus Hunters”

“We were very surprised,” said Dr. Vernon Lee, head of Singapore’s Ministry of Health’s Infectious Diseases Department. “People who didn’t know each other fell ill without any symptoms.”

These new cases did not fit into the picture of what was then known about Covid-19.

Therefore, Dr. Lee, together with his colleagues, with the help of police and special “virus hunters” began an investigation, creating a detailed map of when and where the infected were. This process has been called “contact detection” and is now widely used in the UK and many other countries. The process is to identify all those involved in the outbreak in order to eradicate it.

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At the beginning of the pandemic, Singapore was considered a shining example of combating the spread of coronavirus

In just a few days, investigators interviewed 191 parishioners of the same church and found that 142 of them attended the service on Sunday. It was also quickly discovered that two sick Singaporeans were on duty with the Chinese couple.

“They could talk, shake hands during that service,” says Dr. Lee.

This was an important step in the investigation that could explain how the infection was transmitted. But it remained unclear how the Chinese could transmit the virus if they had no symptoms at the time.

A much more complex mystery remained unanswered. They confirmed the illness of another woman, who, however, was not in that church service. However, she still went to church that day, only a little later. And scientists couldn’t figure out how she could catch the virus?

Evidence that no one expected

Surveillance camera recordings made that Sunday were examined. And they found out something completely unexpected. It turned out that the infected woman, who had attended church after the Chinese had left, was sitting in the same chair that had been occupied by a couple a few hours earlier.

It turned out that although the husband and wife had no symptoms of the disease and felt normal, they were still carriers of the virus. It is not known whether the virus spread to their stools or was released during respiration. However, the consequences were the most serious.

When Dr. Lee compared all the evidence, he had only one explanation: the virus was transmitted by people who were infected but unaware of it. This discovery was of great importance to the whole world, because so far all the recommendations for the coronavirus were limited to recognizing the symptoms in themselves and others.

But if the virus spreads without symptoms, quietly and unnoticed, then how can you stop this disease?

“Every time you make a scientific discovery, you want to shout ‘Eureka!’ You realize that through the hard work of individuals and whole teams, you’ve realized something very important,” recalls Dr. Lee.

Pre-symptomatic infection

And the discovery was the so-called “asymptomatic infection” – when a person does not yet know that he is a carrier of the disease, because cough, fever and other classic symptoms have not yet appeared.

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When Singapore decided to take control of the coronavirus, the number of those infected began to rise again.

A new study has shown that a day or two before the onset of symptoms, people may already be carriers. This is probably the most dangerous period.

Potentially, this is a very important factor, because as soon as you realize that you are ill, everyone who has been in close contact with you can be warned about the need for self-isolation.

That is, isolation can be provided during the infection phase, when symptoms have not yet manifested. However, the question of how the disease can spread without a cough, during which viruses enter the air, remains open.

One version is that infection can occur during conversation and simply during breathing. If the virus reproduces in the upper respiratory tract, it is possible that some viruses are released with each exhalation. And anyone around, especially indoors, can be easily infected.

Another potential for spread is by touch. The virus can get on your hands when you touch an infected person or the door handle – or during a church service. Whatever the route of infection, people lose vigilance when they are unaware of the possibility of catching the disease.

Some symptoms do not appear at all

This is an even more mysterious scenario, and scientists do not yet have an answer to it. After all, it is one thing to know that people can be carriers without symptoms, and quite another – when people get sick, but the symptoms do not appear.

This infection is called asymptomatic because the person is a carrier but not sick. One of the most striking historical examples is considered to be an Irish cook who worked in New York at the beginning of the last century.

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In all the families where Mary Mallon was hired to cook, people contracted typhus, and at least three people died from the disease. At the same time, Mary herself remained completely healthy.

Eventually, the connection between the disease and the cook was established, she was a carrier of the infection, although she remained healthy. The press dubbed her “typhoid Mary,” and authorities sent the woman to quarantine on a remote island, where she spent 23 years before her death in 1938.

You can’t be sure of anything

23-year-old nurse Amelia Powell was shocked to learn that she was an asymptomatic carrier of the infection. When the doctor called her to report the results of the tests, she was working in the ward of the Cambridge clinic in Addenbrook.

Amelia felt normal and felt completely safe, as she used personal protective equipment when working with patients with Covid-19. However, all her confidence instantly disappeared when the tests gave a positive result.

“It felt like I was told about the death of a loved one, it was something unreal. I thought it could not be, but not with me, because I’m fine,” – says Amelia.

She had to leave work immediately and isolate herself at home.

“Of course, I was worried, because I saw the other side of the situation – how quickly the condition of patients with coronavirus is deteriorating, and I thought what would happen to me.” However, to her great surprise, she never fell ill. “Nothing happened to me: at home I continued to exercise, ate normally, slept normally,” says Amelia.

No one knows how many such cases of latent infection there are in the world.

Amelia learned that she had coronavirus only because all hospital staff were required to be tested. Its result surprised experts: out of more than a thousand people, about 3% showed a positive result without showing any symptoms.

Even more asymptomatic infected were found on the cruise liner Diamond Princess, which the epidemic found off the coast of Japan. The liner was dubbed the “Petri dish”, ie a real breeding ground for infection, because about 700 cases of infection were found on board.

At the same time, three quarters of those infected did not show any symptoms.

And in one nursing home in Washington, DC, more than half of residents tested positive for coronavirus but showed no signs of the disease.

There is no reliable data

Different studies provide completely different data on the number of asymptomatic cases ranging from 5% to 80%. This conclusion was reached by Professor Carl Genegan of Oxford University, who together with colleagues studied the results of 21 research projects on this topic.

The general conclusion? According to scientists, no study can provide reliable data on the number of asymptomatic infected. Moreover, if tests for Covid-19 are taken only in people with symptoms, then a certain number of cases will not be taken into account, perhaps significant, experts add.

The danger of “silent distributors”

Nurse Amelia was most worried about being able to inadvertently infect colleagues or patients she cared for.

“I don’t think it happened because the tests of all my colleagues gave a negative result. But it’s still unpleasant to realize that I’ve been a carrier of the infection for so long,” says Amelia. “It’s very strange, but so far we have a minimum of information.”

An alarming signal for the authorities was the results of a study by Chinese scientists, which show that the number of asymptomatic infected exceeds the number of patients with symptoms.

“Silent spreaders require increased attention in the interests of containment and disease control,” the researchers wrote.

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A group of experts who studied the situation aboard the Diamond Princess suggested that asymptomatic infected people are less contagious than people with symptoms, but they could still be an important source of infection.

“Dark substance” of asymptomatic infection

To find the answer, scientists led by Professor Neil Hall suggest testing for coronavirus in the entire population of Norwich.

“Asymptomatic cases may be the same ‘dark matter’ of the current epidemic,” said Professor Hall. It is a notorious invisible substance, which probably consists mostly of the matter of our universe, but which has not yet been discovered.

Professor Hall fears that asymptomatic cases, despite all public health measures, continue to fuel the current epidemic.

“If there are people who are unaware that they are sick, and at the same time use public transport and medical facilities, it inevitably leads to an increase in cases of infection, – says the scientist. – Any action against people who seek medical treatment from symptoms of the disease will be only a partial solution to the problem. ”

According to a group of scientists from California, asymptomatic carriers are the “Achilles’ heel” of our fight against the coronavirus pandemic.

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China was the first to introduce the practice of mass testing for coronavirus

They are convinced that the only way to stop the spread of the disease is to detect all those infected by testing, regardless of whether they have symptoms of the disease.

And they offer to pay special attention to employees of the health care and social security system who are in contact with the risk group.

A similar approach, only on a larger scale, has already been introduced in the city of Wuhan, which became the first outbreak of the epidemic.

There, 6.5 million residents protested for 9 days to find all the carriers, including the hidden ones.

Abolition of strict quarantine

As quarantine measures weaken and more and more people start using public transport, commuting and shopping, the risk of invisible risks increases significantly. At present, it is simply impossible to say who in the crowd may be the involuntary carrier of the infection.

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More and more countries are introducing mandatory wearing of masks

That is why governments explain to their citizens how important it is to work together to identify all those infected and to follow the rules of self-isolation. They also remind that one of the most reliable and effective means of protection is social distance. Well, where this is not possible, you should wear masks, even homemade.

When the US government announced these measures, it referred to the discovery made in the church of Singapore in January. That is, you need to think not only about your own protection, but also about the protection of those around you.

Many health experts fear that wearing masks can distract people from hand washing, social distancing, or even increase the risk of infection if these masks are used improperly. However, more and more countries are convinced of the effectiveness of masks.

It is clear that wearing a mask will not stop the pandemic, but we still know too little about asymptomatic infection with the virus, so any attempt to avoid it is worth it.

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