What's the problem?

There has been plenty of advice and information about the symptoms of COVID-19, with experts stressing the importance of testing and isolating should someone experience any of the known ones. 

However, there have been many cases of people being carriers without displaying any symptoms – therefore not knowing they have the virus and possibly spreading it to others.

In October, epidemiologists at University College London (UCL), published a study on asymptomatic and potential "silent" transmitters of the virus.

Irene Petersen and her colleagues found that 86 percent of those who tested positive for COVID-19 during the first lockdown in England, did not have any of the virus symptoms. 

It used data from the Office for National Statistics (ONS) Coronavirus (COVID-19) Infection Survey pilot study, which looked at the association between symptoms and test results. 

It is one of the first studies exploring the link. It included data from a representative population sample of 36,061 people living in England, Wales and Northern Ireland.  

The data showed 115 people out of the total 36,061 people in the pilot study had a positive test result. Of those with a positive result, only 16 who had reported symptoms on the day of the test did not report any specific symptoms when they were tested. 

"We thought that's a lot of people actually who may not know that they are infected and that may have implications for how the infection is transmitted at the moment," says Petersen.

The study has also highlighted the need to test much more widely.

 

 

What's the worst that can happen?

"The worry is that if you don't have any symptoms, you may not be aware that you can transmit COVID-19 to other people," warns Petersen. "If you are pre-symptomatic, you may not be aware of it, and therefore you may still go to work and go to school and be close to your family or friends.

"And you are actively transmitting the disease because you have no idea that you have the infection, and that way you may have what we call silent transmission."

The other issue is that some of those who have had the infection have gone on to develop what is known as "long COVID-19," which in certain cases can affect the patient's heart health or damage their lungs. 

 

CLICK: THE SCIENCE SHOW YOU NEED IN YOUR LIFE

 

What impact does asymptomatic COVID-19 have on the heart?

Early research found a large portion of deaths caused by COVID-19 were related to cardiovascular problems and heart damage was prevalent in a percentage of people hospitalized for the virus.

But more recently, what has worried scientists and researchers, is the evidence of heart damage reported in mild or asymptomatic cases.

"We've understood that it is not just about the acute infection, it is also what comes afterwards," says Valentina Puntmann of the Institute for Cardiovascular Imaging at Goethe University, Frankfurt. "And many patients who have recovered, actually suffer long-term consequences, such as joint pain, shortness of breath, neurological symptoms and so on.

"So we actually stumbled on the heart being part of it more or less by coincidence."

Puntmann's team decided to scan patients after they had recovered from the acute illness. 

This, to a certain extent, brought them to patients who did not have severe symptoms during the acute phase. 

"Many of them had a bit of a temperature but that was it. So in terms of typical COVID-19 symptoms, they didn't always have them," says Puntmann. "We were quite surprised by what we found [about its impact] on the heart because we did not expect this to be very honest.

"We were shocked to see that 78 percent of them have had something on the heart that we could relate to [the] COVID-19 infection. This was mainly inflammation of the heart muscle, that is myocarditis, but also pericarditis, which is inflammation of the heart's lining."

Putting it all in perspective, Puntmann explains that about a third of patients have very severe myocarditis, which is the active inflammation of the heart. 

"This may or may not be prominent in terms of symptoms, so some people may not be aware of that," adds Puntmann.

 

 

How does asymptomatic COVID-19 affect the lungs?

Daniel Jacobson, the lead researcher for computational systems biology at Oak Ridge National Laboratory in Tennessee, U.S., has been leading a study to understand how COVID-19 affects human body systems. 

The research suggests that health risks to asymptomatic coronavirus carriers could be more significant than previously realised, with as many as half of them going on to develop varying degrees of damage to their lungs.

"There may be a fair amount of damage going on that they're completely unaware of. But they can go from asymptomatic to a 'long hauler' with long-term outcomes," adds Jacobson.

"If all that is true, that really should change how we think about this disease, even from a public health perspective," warns Jacobson. "Because an asymptomatic infection can lead to a long-term disability [and] that [can have] a radical impact on society."

This could explain why some COVID-19 patients have suffocated even when on ventilator support.

 

 

What do the experts say?

Petersen and her peers have not yet been able to establish if it is primarily young and fit people who tend to be asymptomatic or whether other population groups may also fall into this category of COVID-19 carriers.

Moreover, some of the asymptomatic patients can go on to develop symptoms, so they are essentially pre-symptomatic at the testing stage. 

Experts are finding it difficult to distinguish between the two groups.

"It's not just about yourself, it's also about the people you care about," cautions Petersen. "It's about your family and to look after them, so, you may be fine, but your friends and your family may get really bad COVID-19. 

"So if you know that you have been near somebody, think about it and isolate. I say, try to break the chains."

Petersen is optimistic that mass testing could be a way to stop the spread of the virus. 

"I'd really strongly encourage people to get tested because that is probably the best way you can keep the virus under control until we have a vaccine," advises Petersen.

On the other hand, Puntmann believes that scientists must adopt a proactive approach and is keen on building on the expert knowledge gathered over the years about the inflammatory conditions of the heart.

"I think this is something that we as a community have to sort out very soon," advocates the cardiologist. "We know that for some patients this does not end well and we need to look after them."

Video Editing and animations: Paula Harvey

 

Read more: Should I Worry About... Gender-biased AI • Negative interest rates • Atmospheric ammonia • AI deepfakes • EU border policy • Children gaming • Knife crime • Trust in politics • Gang databases • Fast fashion • Flying during COVID-19 • Food shortages • RSI from working at home • Children and coronavirus • COVID-19 conspiracy theories • Catching COVID-19 twice • My dog during the pandemic