True toll of ‘silent carriers’ may be many times higher

THE number of “silent” coronavirus cases may be much higher than thought after a study of cruise ship passengers showed that eight-in-10 of those who tested positive for COVID-19 had no symptoms.

Researchers charting the enforced isolation of cruise ship passengers during the pandemic found that the overwhelming majority of coronavirus patients were symptomless.

Experts warned that the results could have significant implications for the easing of lockdown restrictions and heighten the need for accurate global data about the number of people who have been infected.

The ship with 128 passengers and 95 crew departed from Argentina in midMarch.The first case of fever was reported on the cruise’s eighth day.

Passengers were confined to their cabins, and crew were required to wear PPE.

When the ship docked in Montevideo, Uruguay, five days later, eight passengers and crew had to be evacuated to hospital for respiratory failure and, a week later, more than half of the remaining 217 people on board tested positive for coronavirus.

Of those testing positive, 24 (19 per cent) had symptoms, but 108 (81 per cent) did not. In early March, the World Health Organisation suggested that just one per cent of Covid-positive patients were asymptomatic.

In 10 instances, two passengers who shared the same cabin did not return the same test result – possibly due to the substantial number of false negative results associated with current swab testing methods.

The ship had no contact with other people for 28 days after its departure, so was the equivalent of a sealed environment.

Professor Alan Smyth, joint editor of the journal Thorax, said: “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.”