'Silent' COVID-19 More Widespread Than Thought

Henrietta Brewer
May 28, 2020

Passengers and crew were screened for Covid-19 symptoms, body temperatures were taken before boarding, and no-one who had recently travelled through countries with high infection rates at the time such as China and South Korea was allowed on. Hand sanitizing stations were plentiful aboard ship, particularly in the dining room.

Researchers also said the study demonstrated the pertinence of blood tests for diagnosing individuals who have recovered from Covid-19.

The results of the testing, which were published online today in the journal Thorax, showed that 59 per cent of those on board tested positive for coronavirus.

"We knew that people with severe forms of the disease developed antibodies within 15 days of the onset of symptoms", said Arnaud Fontanet, head of the global health department at the Institut Pasteur, which conducted the research with the University Hospital in Strasbourg.


One of the most important findings of the study, the researchers said was that the majority of COVID-19-positive patients, about 80 per cent, did not exhibit any symptoms.

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, they said.

The ship left in mid-March from Argentina for a planned 21-day cruise of the Antarctic, along a similar route taken by explorer Sir Ernest Shackleton in the early 1900s.

By day 13, eight passengers and crewmembers - many of whom were over the age of 60 or had underlying conditions - required medical evacuation for respiratory failure. In addition, on day 20, all passengers and crew were swab tested for coronavirus.


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

The study authors also said that the potentially high rate of false negative results obtained with current swab tests suggests the need for secondary testing. However, of those who tested positive, only 19 per cent (24 passengers) had symptoms, and 81 per cent (108 passengers) had no symptoms.

In a linked blog, Professor Smyth acknowledged that while it is hard to find a reliable estimate of the number of symptomless COVID-19-positive patients, the figure of 1% suggested by the World Health Organization in early March falls far short of that found on the cruise ship.

Smyth added the findings have implications for easing lockdown restrictions around the globe, given the possibility more people may have been infected with COVID-19 than previously believed.


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