Researchers say their findings indicate that far more people have been infected with COVID-19 than the numbers show

By Julie Mazziotta
May 28, 2020 04:09 PM
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On a cruise ship with a high number of COVID-19 cases, more than 80 percent of the patients did not show any symptoms, a worrying sign that the virus can quietly spread without warning signs.

Researchers in Australia studied a ship of passengers and crew on a 21-day cruise from Argentina to the Antarctic Peninsula, which left in mid-March, after the World Health Organization declared the new coronavirus a global pandemic. Three days into the trip, they decided to end the cruise early, at their next port docking on day 14.

But by the eighth day at sea, a passenger reported having a fever. All passengers were then required to isolate in their rooms until the end of the trip, but the virus spread quickly — of the 217 passengers and crew on board, 128 tested positive for COVID-19.

And of those 128, just 24 showed symptoms. The remaining 104 COVID-19 patients, or 81 percent of the ship, were asymptomatic.

The researchers say these results, which have been peer-reviewed and published in the journal Thorax, indicate that COVID-19 is a "silent infection" that has spread at a higher rate than what is known.

“It is difficult to find a reliable estimate of the number of COVID positive patients who have no symptoms,” Alan Smyth, professor of child health at the University of Nottingham and joint editor-in-chief of Thorax, said in a blog post about the study. “… 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.”

Smyth added, though, that this may mean that more people have unknowingly had COVID-19 and “these individuals may have immunity.” At this point, however, it is not yet known if people who had COVID-19 are immune to getting it again.

The “urgent” need now, Smyth said, is for “accurate” antibody testing worldwide to get a better understanding of how many people have had COVID-19. Though antibody testing is becoming widely available in the U.S., many of the tests may not be accurate, the Centers for Disease Control warned this week.

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