Quarantine. It’s not a word anyone ever wants to hear applied to them. Sometimes, quarantines are necessary and helpful in suppressing viral or bacterial outbreaks. Perhaps even with regard to coronavirus COVID-19. But what if the quarantine makes the problem worse?
In the case of the cruise ship Diamond Princess, that’s exactly what happened, according to researchers at Umea University in Sweden. The ship sat in quarantine for more than two weeks. The result? More coronavirus-infected passengers than if they’d all been taken off immediately. Pretty much the opposite of what was intended.
“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,” says Joacim Rocklöv, Professor of epidemiology at Umeå University and principal author of the article.
It all began with one passenger aboard the cruise ship disembarking in Hong Kong and testing positive for COVID-19. As a result, when the ship reached Yokohama, it was met with a very unhappy message: nobody gets off.
The 3,700 passengers had their vacations disrupted when Japanese authorities would not allow them to leave the ship. It’s been reported that 10 people were infected at the start of the 14 day quarantine on February 5. (1) When it ended on February 19, 619 passengers had been infected by COVID-19 coronavirus. (2)
When the initial quarantine was lifted, a new 14 day quarantine began – for the crew members. They had been living communally in lower deck quarters, making the risk of infection and transmission greater than for the passengers. They were quarantined in the guest quarters. Nice upgrade, lousy reason.
“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. 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. The precautionary measure of putting the entire ship under quarantine was understandable, but due to the high risk of transmission on the ship, the decision is now questionable,” says Joacim Rocklöv.
So was the quarantine worth it? Maybe, say the authors. They estimate that without any precautionary measures, the passengers leaving the Diamond Princess who were potential carriers likely would have infected an additional 2,300 people.
While the quarantine may have contributed to a rise in the number of COVID-19 cases on board the Diamond Princess, there’s a good chance it prevented a larger number of them from occurring. At least, that’s what the science-types at Umea University think.
I have a feeling the passengers stuck on that cruise ship and largely confined to their quarters might not feel so good about that.
Keep the faith and keep after it!
- A Wilder-Smith, H Sjödin, J Rocklöv. COVID-19 outbreak on the Diamond Princess cruise ship: estimating the epidemic potential and effectiveness of public health countermeasures. Journal of Travel Medicine, 2020; DOI: 10.1093/jtm/taaa030