A man navigates with his boat next to cruise ships docked at the port of Long Beach during the COVID-19 Coronavirus pandemic on April 11, 2020 in Long Beach, California.
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More than 80% of passengers and crew infected with coronavirus on an expedition cruise ship showed no symptoms, raising questions about the true incidence of “silent”
The three researchers said their results underscore the need for accurate global data on the number of people, both symptomatic and asymptomatic, who have been infected with coronavirus.
“It is difficult to find a reliable estimate of the number of COVID-positive patients who have no symptoms,” said Alan Smyth, professor of child health at the University of Nottingham and joint editor-in-chief of Thorax, in a statement. “When countries go out of lockdown, a high proportion of infected, but asymptomatic, individuals may mean that a much higher proportion of the population than expected may have been infected by COVID.”
It is still unclear what a greater incidence of infection would mean. The World Health Organization warned earlier Wednesday that it is unknown whether people infected with the corona virus are at risk of becoming infected again.
Researchers have tried to determine the number of asymptomatic Covid-19 patients by conducting antibody test studies, which detect whether someone has previously been infected by the virus. However, such tests have been damaged by accuracy problems and it is still unclear how many asymptomatic carriers there are and how infectious they are.
The researchers’ results come from observations on board a 21-day expedition cruise to Antarctica. All three researchers said they were aboard the ship, which sailed from Argentina in mid-March, after the WHO declared the coronavirus as a global pandemic. The researchers did not explain any funding for the study.
After eight days aboard the ship, the first case of fever was reported, the researchers say. They added that the ship immediately adopted preventative measures, including limiting passengers to their cabins, stopping most daily services, and requiring crew members to carry shelter.
Of the 217 passengers and crew who remained on the ship throughout the trip, 128 tested positive for coronavirus, the researchers said. They added that of those who tested positive, 24 showed symptoms and 108, or 81%, did not.
The researchers did not specify which test was used, but found that it had a high degree of false negatives, which may explain 10 situations where passengers sharing the same cabin tested differently.
The researchers said their results are particularly important to the cruise industry, which has stalled the silence of the coronavirus pandemic. Earlier this year, when the virus emerged, cruise ships in Japan and elsewhere became the site of major outbreaks that led to onboard deaths and crew members quarantined at sea for weeks.
The industry is struggling to return to service, led by the world’s largest cruise operator, Carnival Corp., which is scheduled to resume sailing on August 1.