Another feature of COVID-19 which makes the disease more mysterious.
The more we know about the coronavirus, the stranger it gets.
People with COVID-19 have been reported to show a wide range of symptoms, but some who become infected are symptomless.
Scientists have discovered that the ‘silent’ COVID-19 infection cases are far greater than we know.
Silent infections may be the most bizarre feature of COVID-19.
Since many people can be infectious but show no signs then the transmission rate will increase dramatically.
The typical symptoms, like high temperature and cough, can make a person aware of being infected and lower the odds of spreading it.
Still, it is not clear how the infection can be spread so rapidly without a cough or sneeze where the droplets containing the virus hit a surface.
But most infections are probably due to touching, talking, or breathing into someone’s face or on a surface like door knobs.
The discovery of a much higher incidence of symptomless COVID-19 cases comes from a study tracking isolated cruise ship passengers through the pandemic.
The study found that more than eight out of ten passengers and crew showed no signs of infection while testing positive.
The ship left Argentina in mid-March for a 21-day expedition to Antarctica.
Through these three weeks passengers were not allowed to board in countries with high cases of coronavirus infection.
Also, before embarkation their temperature was taken and there were plenty of hand sanitising stations on board.
On day 8 of cruising it was a case of fever which caused immediate control measures to be taken against infection.
Passengers were kept in their cabins and except for the delivery of meals all other daily services were stopped.
Also, crew members had to wear personal protective equipment if they came in contact with a sick person.
On day 20, a swab test was done on all the passengers and crew revealing that 59 percent of them were positive for coronavirus.
Only 19 percent of those tested positive had symptoms while 81 percent were symptomless.
Interestingly, for 28 days the ship had no contact with the outside environment meaning it was like an airtight container.
The authors expect that the incidence of coronavirus infection on cruise ships is considerably underestimated.
Therefore, they advise that passengers, after getting off a ship, should be monitored to avoid the possible spread of infection.
Professor Alan Smyth, commenting on the study, said:
“It is difficult to find a reliable estimate of the number of COVID positive patients who have no symptoms.
But the figure of 1% suggested by the WHO in early March falls far short of that found on the cruise ship.
As countries progress out of lockdown, a high proportion of infected, but asymptomatic, individuals may mean that a much higher percentage of the population than expected may have been infected with COVID.”
The study was published in the journal Thorax (Ing et al., 2020).