Researchers say there could be many more people with COVID-19 in the community.
Researchers say there could be many more people with COVID-19 in the community.

Silent virus risk bigger than thought

More people could be walking around with coronavirus and not know it, a new study has found.

Australian researchers warn there may be a "higher proportion" of people not showing symptoms of the infection than previously thought.

The scientists were on board a cruise ship to Antarctica during the current pandemic and found more than eight out of 10 of passengers and crew who tested positive for the infection had no symptoms.

There were 128 passengers and 95 crew on the 21-day expedition that left Argentina in mid-March and everyone was screened and tested for coronavirus.

Researchers said 128 people tested positive and the majority - 81 per cent - were asymptomatic.

They concluded "the prevalence of COVID-19 on affected cruise ships is likely to be significantly underestimated, and strategies are needed to assess and monitor all passengers to prevent community transmission after disembarkation".


Researchers say there could be many more people with COVID-19 in the community.
Researchers say there could be many more people with COVID-19 in the community.


Professor Alan Smyth, editor of Thorax, the journal the study has been published in, said the results had implications for the easing of lockdown restrictions.

He said the findings emphasised the pressing need for accurate global data on how many people had been infected.

"It is difficult to find a reliable estimate of the number of COVID positive patients who have no symptoms," Professor Smyth said.

He said the figure of 1 per cent suggested by the WHO in early March fell far short of that found on the cruise ship.

"As countries progress out of lockdown, a high proportion of infected, but asymptomatic, individuals may mean that a much higher percentage of the population than expected may have been infected with COVID," he said.





Passengers who had passed through countries where COVID-19 infection rates were already high in the previous three weeks were not allowed to board the cruise, which was well fitted out with hand sanitising stations, particularly in the dining room.

The first case of fever was reported on day eight, prompting the immediate adoption of infection control measures.

This included confining passengers to their cabins, stopping daily servicing - apart from the delivery of meals - and the wearing of personal protective equipment for any crew member in contact with sick passengers.

By day 13, eight passengers and crew required medical evacuation to hospital for respiratory failure.

On day 20 all the remaining 217 passengers and crew were swab tested for coronavirus.

In 10 instances, two passengers sharing the same cabin didn't have the same test result.

Researchers suggested this was because the current swab test returned a substantial number of false negative results.

They recommend cruise passengers should be monitored after disembarkation to ward off potential community spread of the virus.

With the potentially high rate of false negative results obtained with the current swab tests, they also believe secondary testing is warranted.


Originally published as Silent virus risk bigger than thought