Policy makers may be 'significantly underestimating' the prevalence of COVID-19 on cruise ships, according to the authors behind a report which examined all the passengers and crew on an isolated vessel, in what may be the first study of its kind.
81 per cent of passengers and crew who tested positive for the coronavirus disease 2019 (COVID-19) showed no symptoms of the illness, according to a new peer-reviewed study published in Thorax, a specialist publication from the British Medical Journal. The ship, whose identity has been withheld in order to safeguard patient confidentiality, travelled from Argentina with plans to sail round parts of the Antarctic Peninsula and retrace the route taken by early-19th century British explorer Ernest Shackleton.
However, the voyage was cancelled into the third day of the trip due to newly announced COVID-related international border controls. The vessel found itself unable to return to Argentina and was forced to make its way to Uruguay.
Australian co-authors of the study, expedition physician Dr Jeffery Green and professor of respiratory medicine Alvin Ing, explained the the significance of their findings.
Sputnik: According to your study over 80 percent of the 227 passengers and crew who tested positive for COVID-19 had no symptoms of the illness.
What, if anything, new has been discovered about COVID-19 and how will your findings assist governments and medical experts in tackling the virus?
Dr Jeffery Green: Some passengers had minor Upper Respiratory Tract Infection symptoms which they didn't report but Governments will need to take that mostly Covid spreads on symptom free patients and not wait for symptoms, it also illustrates the ineffectiveness of Temperature as a mass screening tool
Professor Alvin Ing: Yes agreed - To give the correct statistics 128 tested positive (59 percent), of those 24 had symptoms including the 8 that were evacuated. 104 (81 percent) did not report symptoms
Sputnik: How statistically significant is a sample size which involves 227 people and what kind of study needs to be done to conclusively determine the percentage of any given population with COVID-19 who will be asymptomatic?.
Professor Alvin Ing: The ship's population is not reflective of the general population as it is an isolated environment with passengers and crew living in close proximity. However it does highlight that the percentage of asymptomatic Covid positive subjects may be a lot higher than previously thought. The true incidence in a general population will be unknown unless there is widespread testing and not just purely based on symptoms.
Sputnik: For how long did the researchers examine the passengers and crew; could they have developed symptoms after the researchers left the ship?
Dr Jeffery Green: All passengers were taken to Government isolation.
Professor Alvin Ing: This paper only addresses the passengers until disembarkation in Montevideo. We are doing a follow up study to address these questions. I can say however of the 90 Australian passengers who were monitored in Melbourne during mandatory isolation for two weeks after arriving back in Australia, is that none required hospitalisation, with 1 passenger only taken from the plane to hospital for 6 days.
Sputnik: To what extent are the testing kits used and is there a need for more accurate testing kits to be developed?
Dr Jeffery Green: Antibody point of care test kits were unhelpful but used very early. Swab PCR RT [real time polymerase chain reaction] tests seemed useful.
Professor Alvin Ing: Rapid antibody tests are unreliable and unvalidated. Current serological tests for IgA/M/G are by the more conventional methods of immunoflourescence or virus neutralisation which are much better validated.
These are the Covid antibodies, IgM looks at recent infection and IgG looks more at past infection. The immunoflouresence and virus neutralisation are laboratory methods to test these antibodies and are much more reliable than the rapid tests.
Proper validated reverse transcriptase polymerase chain reaction (RT-PCR) was subsequently done on all subjects [to confirm whether they had the virus or not].
Sputnik: What are the researchers/you calling for now as a result of this study, should the findings result in policy changes?
Professor Alvin Ing: We feel that all returning travellers symptomatic or not should be monitored after arrival. In Australia and New Zealand this is achieved with a mandated 14 day isolation. Community testing should also be much broader if there is such a high percentage of asymptomatic covid positive individuals.
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