- In mid-March, a cruise ship departed from Ushuaia, Argentina, and set sail towards Antarctica following explorer Ernest Shackleton’s 1915 route. The passengers and crew aboard didn’t know their ship would become a floating Petri dish of C19.
- Eight days after embarking, the first passenger got a fever and the cruise ship instituted isolation and testing measures. Almost two weeks later, 59% of the 217 passengers and crew tested positive for C19. Out of that group, more than eight out of 10 had no symptoms.
- In a study released Thursday in the journal Thorax, scientists report that these findings suggest ‘silent’ symptomless C19 infections — the sort experienced by asymptomatic carriers — may be far more common than previously thought.
- The cruise offered a unique testing ground for study co-authors Alvin Ing and Christine Cocks, scientists who were on board as passengers, and co-author Jeffrey Green, the expedition physician. They witnessed C19 unfold in the unique, isolated environment in real-time, and began their study before they could disembark.
- Their report is another example of the fact that C19 can spread like wildfire on cruises, which often have semi-crowded public spaces, close quarters, and older travelers. The findings can also be extrapolated to other scenarios such as aged care facilities and migrant camps, the study’s authors tell Inverse.
- “The high rate of asymptomatic C19 patients may mean there may be higher rates of immunity to C19 in the general population than we currently are aware of,” Ing, a respiratory and cardiovascular medicine researcher at Macquarie University, tells Inverse. At this point, scientists don’t know yet how much protection C19 infection creates against future reinfection.
- “Being free of symptoms does not equal being free of infection,” Alan Smyth, joint editor-in-chief of the journal Thorax and researcher at the University of Nottingham, tells Inverse. He was not involved directly in the study but published a related commentary.
- The researchers documented how C19 spread among cruise passengers and crew and charted the enforced isolation measures put in place.
- On day 20 of the cruise, all passengers and crew were tested for C19. Ultimately, 128 out of 217 people tested positive.
- Just 24 positive patients actually showed symptoms. 16 had fevers and mild symptoms, while four required intubation and ventilation. One person died due to C19 complications.
- Overall, 81% of those who tested positive for C19 were asymptomatic. This doesn’t quite jibe with what we know about asymptomatic patients so far: The CDC reports 35% of infected people may be asymptomatic. Meanwhile, another cruise ship study, this one focused on the infamous Diamond Princess, suggests 18% of infected people were asymptomatic — but not all passengers and crew were tested. This study quadruples that number.
- While the “population” on the cruise ship was small, every single member of this population was tested. This makes this cruise a unique “natural experiment” that can’t be repeated elsewhere, Smyth says.
- “There is no reason why the passengers and crew on the ship are any more likely than the general population to be infected with C19 but have no symptoms,” he adds.
- “It is therefore very plausible that the rate of 81% infected but symptom-free might apply to the general population. This means that many more people may be potentially immune than was first thought.”
- Currently, testing hasn’t fully captured how many asymptomatic C19 positive people are out there. But this study suggests the number may be higher than anticipated, and testing only symptomatic people may be missing a huge proportion of infected people.
- “Testing just symptomatic subjects in such an at-risk environment is likely to miss a significant population with C19, and may thus promote community transmission if untested or unmonitored,” Ing says.
- “If we are serious about preventing a second wave of C19 infection, then it is vital that we have widespread accessible community testing, and the ability to rapidly trace and isolate contacts.”
Source: Cruise ship study exemplifies the danger of asymptomatic patients