The number of people with Covid-19 who are asymptomatic could be much higher than previously thought, according to an analysis of a cruise ship outbreak published today.
The study found more than eight out of ten on a cruise ship tested positive with no symptoms.
The findings of the Australian study, published in the latest edition of Thorax, emphasise the need for accurate global data on how many people have been infected, say the authors.
The three researchers – from Macquarie University, Sydney, Sunshine Coast University Hospital, Queensland, and the Royal Australian College of General Practitioners, Victoria – were on board the cruise expedition ship carrying 128 passengers and 95 crew at the time, which departed from Ushuaia, Argentina, for a planned 21-day cruise of the Antarctic.
It set sail in mid-March after the World Health Organisation had declared Covid-19 a global pandemic and any passenger who had passed through countries where Covid-19 infection rates were already high in the previous three weeks, were not allowed to board.
Those allowed on ship had their temperature taken and hand sanitising stations were plentiful, particularly in the dining room.
The first case of fever was reported on day eight, which prompted the immediate adoption of infection control measures of confining passengers to their cabins, stopping daily servicing, apart from the delivery of meals, and the wearing of personal protective equipment for any crew member in contact with sick passengers.
The ship had to sail to Montevideo, Uruguay, because Argentina closed its borders, and arrived there on day 13, at which point eight passengers and crew required medical evacuation to hospital for respiratory failure.
On day 20, the remaining 217 passengers and crew were swab tested for coronavirus and 128 (59%) tested positive. Of those testing positive, only 24 (19%) had symptoms.
In ten instances, two passengers sharing the same cabin did not have the same test result, possibly because the current swab test returned a substantial number of false negative results, say the authors.
The study authors conclude that the prevalence of Covid-19 infection on cruise ships is likely to be “significantly underestimated,” prompting them to recommend that passengers should be monitored after disembarkation to ward off potential community spread of the virus.
And the potentially high rate of false negative results obtained with the current swab tests suggests that secondary testing is warranted, they add.
Ing AJ, Cocks C, Green JP. COVID-19: In the footsteps of Ernest Shackleton. Thorax 28 May 2020
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