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At least 8-in-10 cruise ship passengers who tested positive for Covid-19 went without symptoms, suggesting that “silent” infection may be higher than previously thought. The findings, which are published in the journal Thorax, may have implications for the current easing of lockdown measures around many parts of the world.
"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," said Professor Alan Smyth of the Division of Child Health at the University of Nottingham in a statement.
Researchers describe their experience while aboard a 21-day expedition cruise from Argentina to Antarctica that set sail in mid-March after the World Health Organization (WHO) declared the global pandemic.
Note that passengers who had traveled through countries with high rates of infection were not allowed passage. Despite putting in place recommended precautions such as establishing hand sanitizing stations and temperature monitoring, the first fever case was reported on the eighth day of embarkation, prompting further restrictions for passengers including limiting passengers to their cabins and mandating crewmembers who came into contact with sick passengers wear personal protective equipment.
By day 13, eight passengers and crewmembers – many of whom were over the age of 60 or had underlying conditions – required medical evacuation for respiratory failure. A week later, each of the 217 people aboard the vessel was swab tested – more than half of whom tested positive for SARS-CoV-2. In 10 cases, two passengers sharing the same crew had different test results, highlighting the high likelihood of a false negative result.
Surprisingly, 81 percent of those who tested positive for the severe respiratory disease did not show symptoms. In total, just 24 of the 128 Covid-19 positive patients were symptomatic.
“We conclude that the prevalence of COVID-19 on affected cruise ships is likely to be significantly underestimated, and strategies are needed to assess and monitor all passengers to prevent community transmission after disembarkation,” write the study authors.
The authors add that they believe this is the first stance of complete Covid-19 testing of all passengers and crew on an isolated cruise ship, particularly as the cruise ship had “no outside human contact” and was socially isolated for 28 days.
