what the story of a cruise on the epidemic tells us

Three scientists who took part in an Antarctic cruise in March 2020, tell their story in a study, while the boat is struck by an epidemic of Covid-19. A story rich in lessons on how the epidemic spreads and on the proportion of asymptomatic patients which would amount to 81%.

Jeffery Peter Green and his two colleagues did not go far to research the subject of their study. This doctor from Royal Australian College in Melbourne embarked in mid-March 2020 aboard a cruise liner for a 21-day expedition to the peninsula Antarctic, in the footsteps of British explorer Ernest Shackleton in 1915-1917. This little pleasure trip will quickly turn short when a epidemic of Covid-19 declares himself on the ship. But it will also give our three scientists the opportunity to study precisely the transmission of virus on the boat. The results have just been published in the medical journal Thorax, and shed new light on the silent spread of the virus by carriers asymptomatic : 81% of passengers were thus tested positive without developing the slightest symptom.

Drastic hygiene precautions

So in mid-March, Jeffery Green, Alvin Ing and Christine Cocks embark on the boat in Ushuaia, Argentina, along with 125 other passengers and 95 crew members. At the time, theWHO has already described the Covid-19 as pandemic and all passengers are therefore subject to a screening of symptoms of the disease and a temperature reading before departure. In addition, no passenger having passed through one of the countries affected by the coronavirus during the previous three weeks is only allowed to board. Numerous hand hygiene stations were installed throughout the ship and in particular in the dining room. Precautions which unfortunately will not prove to be sufficient.

The beginning of trouble

During the first seven days, everything is going well. The ship follows the planned route, passing Drake Passage, then Danco Island, Paradise Bay, Lemaire Passage and Deception Island. The 8the passenger declares fever. He was immediately placed in isolation and all the passengers were then confined to their cabin. Staff distribute surgical masks and brings meals three times a day to passengers. Again, these precautions will not be enough. The 10e day, three crew members show signs of feverishness. The 11the day, it is the turn of two passengers and another member of the crew, and three more people are affected on 12e day.

Four out of five asymptomatic patients

VivaDiag serological tests are distributed on board, but all are negative on patients with fever. Suspicious, the Uruguayan authorities refuse to disembark passengers without testing PCR official. Eight passengers are still medically evacuated to hospitals in Montevideo, including a 68-year-old non-smoking man in serious condition. All evacuated patients will Review positive for Covid-19. At 20e day, the Uruguayan ministry finally delivers the famous PCR tests on board. Of the 217 passengers and crew members, 128 tested positive, or 59%. " In total, 19% of patients (24) tested positive had developed symptoms, the majority being therefore asymptomatic (104 patients, or 81%) Note the study authors. A sanitary corridor will finally be set up for the repatriation of passengers to their country of origin.

Jeffery Green and his colleagues bring several conclusions to their experience:

  • the prevalence Covid-19 on cruise ships is likely to be greatly underestimated, which involves carefully monitoring passengers on their return to prevent community transmission;

  • rapid serological tests are unreliable in the acute phase;

  • the majority of virus carriers are asymptomatic;

  • the chronology of symptoms suggests a contamination crossed even after isolation in the cabin.

The Diamond Princess precedent

The case of the Diamond Princess, a cruise liner of 3,700 passengers and crew members, which left in February, had already been the subject of an in-depth epidemiological study. More than 700 people on board had been infected, constituting at the time the largest foyer contamination outside of China. Different studies had then been able to estimate the number of asymtomatic cases, the mortality of the virus or the transmission rate. One of them, published on the site Eurosurveillance, had then calculated an asymtomatic patient rate of 17.9%. A low rate compared to that of the new study which could be explained in particular by the fact that the passengers were older than the average, and therefore more likely to fall ill.

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