Quarantine on cruise ship may have increased number of onboard coronavirus cases: Study

Quarantining the cruise ship Diamond Princess, some of whose passengers were infected with the novel coronavirus, may have resulted in more cases of the viral infection than if they would have disembarked immediately, according to a study.

The ship, which was docked at the Yokohama port in Japan, has seen more than 600 infected patients during the quarantine, according to a study, published in the Journal of Travel Medicine.

"The infection rate onboard the vessel was about four times higher than what can be seen on land in the worst infected areas of China. A probable cause is how close people stay to one another onboard a vessel," said Joacim Rocklov, study co-author from Umea University in Sweden.

The researchers said after a person travelling with the cruise ship disembarked in Hong Kong, and was tested positive for the coronavirus, Japanese authorities decided to disallow the 3,700 passengers onboard to leave the ship when it reached Yokohama.

Put in quarantine until 19 February, passengers onboard the ship who showed signs of illness were, as far as possible, separated from other passengers onboard, the scientists noted.

"If the ship had been immediately evacuated upon arrival in Yokohama, and the passengers who tested positive for the coronavirus and potential others in the risk zone had been taken care of, the scenario would have looked quite different," Rocklov said.

"Our calculations show that only around 70 passengers would have been infected. A number that greatly falls short of the over 600 passengers the quarantine resulted in," he added.

According to the researchers, due to the high risk of transmission on the ship, the precautionary measure of putting the entire ship under quarantine is questionable.

But they added that if the precautionary measures of isolating potential carriers had not been carried out onboard, another 2,300 people may have been infected.

"The cruise ship conditions clearly amplified an already highly transmissible disease. The public health measures prevented more than 2,000 additional cases compared to no interventions," the researchers wrote in the study.

"However, evacuating all passengers and crew early on in the outbreak would have prevented many more passengers and crew from infection," they added.