Prevalence of ‘silent’ Covid-19 infections much higher than thought

Grant Boone
May 28, 2020

Even still, the results are a stark reminder of how likely COVID-19 is to spread within communities, and how hard it can be to tell when it does.

"Strategies are needed to assess and monitor all passengers to prevent community transmission after disembarkation", the Australia-based researchers said.

Whether or not people who have been infected are immune to the new coronavirus, the findings emphasize an urgent need for accurate global data on how many people have been infected, he concluded.

The researchers, all of whom were on board the vessel, describe events on an expedition cruise ship carrying 128 passengers and 95 crew.

Note that passengers who had traveled through countries with high rates of infection were not allowed passage.

To reduce chances of the passengers contracting the virus, the researchers said, hand sanitising stations were plentiful aboard the ship, particularly in the dining room.

Researchers also said the study demonstrated the pertinence of blood tests for diagnosing individuals who have recovered from Covid-19.

Paris: Even people with minor illness from the coronavirus can develop antibodies that could leave them immunised for several weeks or more, according to an early French study that tested hospital staff with mild infections.

Melbourne epidemiologist Ivo Mueller told the Australian Science Media Centre: 'If the same pattern is repeated elsewhere, this means that in countries that only test symptomatic cases, the true burden of infections may be five times higher than now reported'.

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Rapid diagnostic tests found antibodies in 153 samples; more complicated S-Flow tests found antibodies in 159.

According to the study, the first case of fever was reported on day 8, prompting the immediate adoption of infection control measures.

As Argentina had closed its borders, the ship sailed to Montevideo, Uruguay, arriving on day 13.

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In 10 instances, two passengers sharing the same cabin didn't have the same test result.

The study authors also said that the potentially high rate of false negative results obtained with current swab tests suggests the need for secondary testing.

Surprisingly, 81 percent of those who tested positive for the severe respiratory disease did not show symptoms.

Professor Alan Smyth, joint editor-in-chief of Thorax, commented in a linked blog that the findings also have implications for the easing of lockdown restrictions, which is now taking place all around the world as many countries start the process of deconfinement.

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