Asymptomatic Cases of COVID-19 Might Be More Common Than We Think

By Sarah Basford on at

As countries across the world begins to re-open public places and venues, the risk of a second coronavirus outbreak is set to increase. While quarantining and isolation measures will continue for anyone showing symptoms, it’s those who walk around without knowing they’re carrying COVID-19 that present the real risk. Two new studies suggests asymptomatic coronavirus cases might be more common than we think.

Two research papers released on Thursday indicated the rate of asymptomatic cases of COVID-19 in their samples was considerable, highlighting the need for extra vigilance as restrictions begin to ease.

The first paper, published in the Journal of the American Medical Association, found 42.3 per cent of the 78 coronavirus patients studied between December and February in Wuhan did not show any symptoms. The study’s authors admitted there were some flaws with isolating the asymptomatic patients immediately but it shows an early example of asymptomatic cases during the virus’ first epicentre.

Australian researchers from Macquarie University and Queensland Health detailed a cruise ship example in another paper published in Thorax, showing the majority — 81 per cent — of the 128 passengers who tested positive for COVID-19 were asymptomatic. It also noted that the ‘rapid tests’ that use blood samples to test for coronavirus couldn’t initially detect patients who were later found to host the virus.

Both papers, while presenting limited studies, add to the growing body of evidence suggesting asymptomatic cases are happening more frequently than first anticipated. Australian experts agree it shows the importance of vigilant testing even when contacts are showing no symptoms.

Professor Raina MacIntyre, a biosecurity expert at UNSW, told the Australian Science Media Centre the papers back up some of the insights and reaffirm the need to test anyone who’s been in contact with a known coronavirus case.

“Studies of the Diamond Princess found about two-thirds of passengers were infected, with a high proportion asymptomatic. Studies in aged care and other outbreaks have also found 50 per cent or more of all positive cases are asymptomatic,” Professor MacInyre said.

“We should not be debating this any longer. High-risk contacts in outbreak situations, whether family contacts or in a closed setting outbreak, should be tested regardless of symptoms or cases will be missed.”

Aside from a few countries that have managed to roll out widespread testing, most countries – including the UK – require people to be showing at least some symptoms before getting tested. With cafes, restaurants and pubs opening back up and regional travel becoming a possibility again, it’s expected that the infection rate could rise again. Keeping testing numbers high will be a key strategy for finding and halting community outbreaks over the coming months.

There is a positive to the frightening idea of all these unseen cases walking through shopping centres or riding on public transport, according to Professor Brian Oliver, a disease expert from University of Technology, Sydney.

“On the positive side, if people are asymptomatic they will not have a runny nose or cough so are unlikely to be a huge danger to society, but of course if people don’t think they have an infection they can be complacent with their own hygiene measures,” Professor Oliver said.

“As we ease the lockdown, it is important that we all remember to wash our hands, and keep to appropriate social distances.”

It’s a sober reminder that once we start to venture outside the home again, it will be important to heed the advice from health authorities around the country. Now’s no time to return to your three-second hand washing ways.

Featured image: Getty


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