'Can I have COVID-19 without knowing?' What you need to know about asymptomatic cases.


Australia’s Chief Medical Officer Professor Brendan Murphy said last week that worldwide cases of COVID-19 could be “five to 10 times” higher than what is currently being reported.

That’s due to a myriad of reasons, including a shortage of testing in most countries. But it also could be due to a high number of people who have contracted COVID-19 without even knowing it.

Not only does that mean many people could have already been infected with the virus without being diagnosed, but it also means many people could have COVID-19 right now, without realising.

So, what proportion of those with coronavirus are symptom-free? And can they transmit the disease to other people?

Here’s exactly what we know.

Firstly, what does asymptomatic actually mean?

The World Health Organisation defines an asymptomatic case as a person infected with COVID-19 who does not develop symptoms.

Watch: Mamamia breaks down your most common questions about COVID-19. Post continues below. 

Video by Mamamia

What proportion of those with COVID-19 are asymptomatic?

This is unclear. Mostly because testing those who are asymptomatic are, for obvious reasons, not being tested nearly as much as people who are displaying symptoms.


However, there is research to give us a fairly good understanding of the proportion of people with COVID-19 who are asymptomatic.

One study examined the outbreak of COVID-19 on the Diamond Princess cruise ship, which in February was put under mandatory quarantine and docked at Yokohama in Japan.

Of the 3,711 passengers and crew members on board, a total of 634 passengers tested positive to COVID-19.

Of those who tested positive, researchers estimate 17.9 per cent were asymptomatic. That’s nearly one in five cases which are asymptomatic.

Gold Coast Beaches Set To Close Due To Coronavirus Restrictions
Many beaches in Australia have been closed in light of the coronavirus pandemic. Image: Chris Hyde/Getty Images.

However, the study explains this number could in fact be much higher for two predominant reasons. Firstly, testing was prioritised for those who were displaying symptoms of COVID-19 - meaning they could have missed lots of people who had COVID-19 but weren't showing symptoms. Secondly, the majority of passengers were 60 years and older, who are more likely to experience more symptoms.

Other research suggests the percentage of asymptomatic cases is much higher.

The US Centers for Disease Control and Prevention (CDC) estimates that as many as 25 per cent of people infected with COVID-19 won't develop any symptoms. That's one in four cases.

In any case, that is a significantly higher proportion than what the World Health Organisation originally reported. In February, they said asymptomatic cases were "relatively rare", and accounted for 1-3 per cent of coronavirus cases.

Can asymptomatic cases transmit COVID-19?

Researchers are still working to determine exactly how contagious asymptomatic cases are.

One study did look at the case of a man in China they call 'Patient Z' who was infected with COVID-19 but showed no symptoms.

"The viral load that was detected in the asymptomatic patient was similar to that in the symptomatic patients, which suggests the transmission potential of asymptomatic or minimally symptomatic patients," the study states, suggesting those without symptoms are indeed still contagious.


The CDC has acted on this research, and state that the "virus can spread between people interacting in close proximity - for example, speaking, coughing, or sneezing - even if those people are not exhibiting symptoms".

For this reason, they have advised all Americans to wear "cloth face coverings in public settings".

Listen: Mamamia's daily news podcast The Quicky looks at what life is like in hotel quarantine in Australia. Post continues below audio.

So... what does this mean?

Well, it firstly means we will probably never know the true number of people who contract COVID-19.

But even more so, it reinforces the critical importance to stay indoors and adhere to the strict social distancing and self-isolation rules put in place by our government.

Just because you don't feel sick, doesn't mean you could not be a silent carrier of the potentially fatal virus.

Read more on COVID-19:

If you are sick and believe you have symptoms of COVID-19, call your GP ahead of time to book an appointment. Or call the national Coronavirus Health Information Line for advice on 1800 020 080. If you are experiencing a medical emergency, call 000.

To keep up to date with the latest information, please visit the Department of Health website.

Feature Image: Getty. 

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