Who is most likely to be an asymptomatic COVID-19 carrier?

Throughout history it has not been uncommon for people to wander around with infections and no symptoms of being sick.

In the early 1900s, Typhoid Mary spread typhoid fever to other people without having any symptoms herself.

And it seems we may have a few like her roaming around right now, if a small Chinese study is anything to go by.

The study from Wuhan University found that people with COVID-19 who don’t show symptoms tend to be younger and are more likely to be women, and asymptomatic people seem to experience less damage to their immune systems than symptomatic patients.

When comparing asymptomatic COVID-19 positive patients with patients who displayed symptoms, researchers found that asymptomatic people still shed the virus, but for a shorter period of time.

The median age of asymptomatic patients was 37, with two in three being women.

No one really knows how widespread asymptomatic COVID-19 infection cases are, but anecdotal evidence suggests that this may be a reason the virus has been so ‘successful’.

“Although patients who were asymptomatic experienced less harm to themselves, they may have been unaware of their disease and therefore not isolated themselves or sought treatment, or they may have been overlooked by healthcare workers and thus unknowingly transmitted the virus to others,” it read.

“Fortunately, patients with asymptomatic SARS-CoV-2 infection have a shorter duration of viral shedding from nasopharyngeal swabs and lower risk of a recurring positive test result of SARS-CoV-2 from nasopharyngeal swabs, which can provide a reference for improving the prevention and control strategies for patients who are asymptomatic.”

Asymptomatic cases are far more common than researchers are comfortable with, too.

In a nursing home in Washington, many residents became infected. Of these, 23 tested positive, 10 were already sick, 10 more eventually developed symptoms, but three people who tested positive never came down with the illness.

Of the 397 people staying at a homeless shelter in Boston who were tested, 36 per cent were positive for COVID-19 but not one of them complained of any symptoms.

Of all the Japanese citizens evacuated from Wuhan and subsequently tested, 30 per cent of those infected were asymptomatic.

And an Italian study found that 43 per cent of those who tested positive for COVID-19 showed no symptoms.

Researchers are still unable to tell the difference between how potentially contagious people with or without symptoms are, but they estimate that anywhere from 10 to 40 per cent of the total number of infected people around the world may not experience symptoms.

COVID-19 has infected more than 5.5 million people and killed more than 350,000 worldwide, but the infection rate could be much higher, with many of those infected being ‘silent carriers’ who show no or very mild symptoms.

Even if someone is not coughing or sneezing, infected droplets can spray from normal exhalations. A regular breath may spread the virus. Research published in the Proceedings of the National Academy of Sciences (PNAS) suggests that talking launches thousands of tiny infected droplets that remain suspended in the air for up to 14 minutes, which could explain “how people with mild or no symptoms may infect others in close quarters such as offices, nursing homes, cruise ships and other confined spaces”.

Surfaces, such as lift or traffic light buttons, doorknobs or shopping trolleys or baskets can also be contaminated with the coronavirus by an infected person’s touch.

The government’s COVIDSafe app is also not helpful in the case of asymptomatic users.

It goes without saying that every day brings another challenge in controlling or even knowing about COVID-19, and that much more data is needed on asymptomatic transmission.

Asymptomatic SARS-CoV-2 infection may be complicating efforts to get the pandemic under control and find a vaccine.

The message in the meantime: stay safe and don’t let your guard down even when no-one’s around.

Do you think you may have had COVID-19 and not known about it?

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Written by Leon Della Bosca

Leon Della Bosca is a voracious reader who loves words. You'll often find him spending time in galleries, writing, designing, painting, drawing, or photographing and documenting street art. He has a publishing and graphic design background and loves movies and music, but then, who doesn’t?
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