Prevalence of silent COVID-19 infection underestimated

A new study published in the journal Thorax has revealed that the prevalence of asymptomatic COVID-19 infection may be drastically higher than what was previously realized. 

The research was focused on passengers and crew members who were isolated during the pandemic on an expedition ship. More than 80 percent of those who tested positive for the coronavirus had no symptoms. 

Professor Alan Smyth, joint editor-in-chief of the journal, said the study has implications for the easing of lockdown restrictions. The findings also highlight the urgent need for accurate data on how many people have actually been infected with COVID-19.

The researchers were all present onboard the cruise ship, which was carrying 128 passengers and 95 crew members. The expedition departed from Argentina for a 21-day tour of the Antarctic. 

The ship disembarked in mid-March after the World Health Organization had declared COVID-19 a global pandemic.

Passengers who had traveled in countries with high rates of COVID-19 infection over the previous three weeks were not allowed to board, and those who boarded had their temperature taken.

The researchers describe having an abundance of hand sanitizing  stations on the ship, particularly in the dining area.

The first case of fever was reported on day 8, and COVID-19 infection control measures were immediately enforced. This included passenger confinement to cabins with no services provided other than the delivery of meals. 

In addition, any crew members in contact with sick passengers wore personal protective equipment.

Argentina had already closed its borders, and the ship arrived in Uruguay on day 13. At this point, eight passengers and crew members required medical evacuation for respiratory failure.

On day 20, the remaining 217 passengers and crew were swabbed for coronavirus, and 128 individuals tested positive.

There were ten separate instances when two people sharing the same cabin had different test results. According to the study authors, this discrepancy is likely due to the fact that the current swab test produces a substantial number of false negatives.

Among those who tested positive, only 19 percent had symptoms of COVID-19 infection, while 81 percent were asymptomatic.

The researchers conclude that the prevalence of COVID-19 infection on cruise ships is likely to be “significantly underestimated.” They say that passengers should be monitored after a cruise ship disembarks to prevent the potential rapid spread of the virus.

“It is difficult to find a reliable estimate of the number of COVID positive patients who have no symptoms,” Professor Smyth wrote in a blog post.

“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.”

The study is published in the journal Thorax .

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By Chrissy Sexton, Earth.com Staff Writer