silent cases of coronavirus may be many more than previously thought

In mid-March, after the World Health Organization (who) COVID-19 declared a world pandemic, a ship departed from Ushuaia, Argentina. Their goal was to take a 21-day cruise through Antarctica, taking a route similar to that of polar explorer Ernest Shackleton in 1915.

A group of researchers led by Alvin Ing, from the Macquirie University Hospital (Australia), which registered the forced isolation of the 128 passengers and 95 crew during these three weeks of expedition. As in the famous series of the 80s Holidays at sea, in which tourists 'found love' aboard a cruise ship, this trip will be remembered for finding interesting scientific results, published this week in the magazine Thorax.

Passengers who, in the previous three weeks, had passed through countries where infection rates by this virus were already high, were not allowed to board. Everyone had their temperature taken before chartering and there were numerous hand sanitizing points throughout the ship, especially in the dining room.

The first case of fever was registered on day 8, which prompted the immediate adoption of control measures. This included the confinement of passengers in their cabins, the interruption of daily services except for the delivery of meals and the use of personal protective equipment for any member in contact with the sick.

As at that time Argentina had already closed its borders, the ship set sail for Montevideo (Uruguay), arriving on the 13th. At this point, 8 passengers and a member of the crew required to be taken to the hospital due to respiratory failure. On the 20th, the remaining 217 passengers and crew were tested for coronavirus. More than half (128; 59%) tested positive.

Of those who tested positive, 24 (19%) had symptoms, while 108 (81%) did not. In other words, more than 8 out of 10 passengers and crew who tested positive were asymptomatic. These figures are well above the 1% of cases suggested by the WHO in early March.

For the authors, this indicates how the prevalence of 'silent' COVID-19 infection may be much higher than previously thought. "If only symptomatic subjects are screened in such a high-risk setting, a significant infected population is likely to be overlooked, which in turn may promote transmission to the community," explains SINC Ing .

"The results could be extrapolated to similar situations, isolated environments in which people live in an enclosed space. On other cruises, nursing homes and migrant camps this is likely to have happened," he adds.

Implications for de-escalation

The authors conclude that the prevalence of COVID-19 infection on cruise ships is likely to be "significantly underestimated," leading them to recommend that passengers be monitored after each landing to avoid possible spread. community.

Furthermore, experts point out that this may have implications for the relaxation of isolation restrictions, thus underlining the "urgent need" for accurate global data on the number of people infected.

"This report is proof of the ease of propagation due to the cases in which the people affected were 'apparently well', even in a forced confinement and without introducing external cases," says Jeffrey Green of the Royal College of Physicians of Australasia and another of the authors.

"If we want to be serious about preventing a second wave of coronavirus infections, then it is vital that we have widely accessible community testing, and the ability to quickly trace and isolate contacts," concludes Ing.


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