What went wrong on the Diamond Princess? Why cruise ships are a hotbed for viral outbreaks

The decision to quarantine some 3,700 people on board the Diamond Princess cruise ship in Japan amid an outbreak of coronavirus is unprecedented. But experts say it's also likely doing more harm than good.

"It would be extremely difficult to end up containing it on a cruise ship, which is sort of like the most obvious place to house people where disease spreads," said Dr. Michael Mina, an epidemiologist and assistant professor at Harvard's School of Public Health. 

"It was really a bad idea from the start."

The U.S. Centers for Disease Control has recorded hundreds of viral outbreaks on international cruises over the past 25 years, with norovirus being the most common with more than 250 cases.

"There's always going to be a risk of transmission of a disease when you've got thousands and thousands of people on board from different backgrounds with different medical conditions," said Dr. Robert Quigley, of International SOS, a security and medical travel risk firm.

"They congregate in public areas and they're in close proximity, because there's only so much cubic space on these cruise ships." 

Quigley says because the illness caused by the coronavirus, now known as COVID-19, is extremely contagious, it's no surprise the Diamond Princess saw case numbers rise since the quarantine began on Feb. 4.

There have been 218 passengers with confirmed cases on the ship, 12 of whom are Canadian, and pressure has mounted to allow them to leave as quarantine efforts failed to contain the outbreak. 

"Some of them are not in quarters that even have windows, let alone balconies, and so it becomes a challenge," he said. "There's so many ways that these people could be further exposed, regardless of the efforts that are being made to keep them in their quarters." 

One key factor with ongoing infections may be the ship's crew, who have been tasked with delivering food and supplies to passengers amid the outbreak.

At least 10 staff members have already been infected, which Mina says was a "turning point" for him in assessing the effectiveness of the quarantine.

"Clearly the quarantine is no longer working," he said. "You're just asking for continued transmission and now that we really know that transmission is occurring on the ship, it really drives the whole question of, what's even the point of this quarantine?"

Does Japan have the right to quarantine the ship?

Every country in the world has "inherent police powers" that allow for the quarantine of certain individuals in extenuating circumstances, said maritime lawyer Jack Hickey. 

"Generally, these kinds of laws are going to be loosely worded to give the authority to the government to do what it needs to do depending upon the circumstances," he said. "But Japan has the right to quarantine a ship."

Hickey said there is also no international standard set out in a treaty that states a specific burden of evidence needs to be met in order to quarantine an entire ship — something not seen since the 1918 Spanish flu pandemic. 

Under Japanese law, quarantine efforts can be put in place to "prevent infectious disease-causing pathogens that are not native to Japan from entering the country via marine vessels."

But there is an obligation on both the Japanese government and Princess Cruises to provide food, supplies and medication to passengers as needed. 

"They have to actively, on a daily basis, take care of the folks," Hickey said. "They have an obligation to treat the passengers reasonably under the circumstances." 

Passengers may also have waived their right to any legal action as a result of the quarantine, as tickets often contain a prohibition on class-action lawsuits. 

"That has been attempted before, but I can't see why it would be enforceable," he said, adding that even if there were a death on the ship, it would still be difficult to hold the company accountable.

"You'd have to look closely at the circumstances and whether Princess Cruises did anything to cause that." 

What other options are there for passengers? 

Japan had limited options for containing the outbreak of coronavirus on the Diamond Princess and government officials had to act quickly.

"The logistics of finding appropriate accommodations for 3,700 people on very short notice would be extraordinarily challenging," said Dr. Isaac Bogoch, an infectious disease specialist at Toronto's University Health Network. 

"So while everyone kept saying, 'Get them off the boat,' and while that's completely reasonable to say, I think we also have to appreciate what some of the logistics of that actually means." 

Aside from commandeering hotel buildings or military facilities for the purposes of housing passengers on land, one other option would be for passengers to leave the ship, self-isolate at home and report any symptoms to health officials.

But that concept isn't "politically palatable," said Dr. Michael Gardam, an infectious disease specialist and chief of staff at Humber River Hospital in Toronto.

"What's been done is the individuals on that ship have been sacrificed for the greater good," he said. "Whenever we quarantine people, it's never good for the person or quarantine — it's good for the rest of us." 

What can we learn from the Diamond Princess outbreak?

While it remains to be seen if a study of the outbreak will be published with more specific details of how the coronavirus spread, one thing we may be able to learn about it as a result of this mass quarantine is how sick it makes people.

"The only good thing to come out of this ship is this is the only time thus far that we have a natural experiment where we're getting a sense of what the spectrum of disease is," said Gardam. 

"Then we can start to tentatively apply some of those numbers to what's going on in the world and start to be a little bit more accurate in what we're talking about." 

In terms of how transmissible the disease is from person to person, Mina thinks any results taken from the ship would be too skewed to glean from.

"I don't really think we're going to learn too much. We already know that this virus clearly transmits well," he said. "So the fact that it's transmitting on a cruise ship, where everyone's in tight quarters, is what really anyone would expect." 

Bogoch agrees that the "artificial environment" on the ship isn't something that can necessarily be applied to the real-world spread of the coronavirus. But depending on the spread from passenger to passenger, we could learn more about its incubation period, he suggests.

There could also be a chance to learn more about the coronavirus itself, Mina says, if there are passengers on the ship who are found to have built up a natural immunity to it. 

If a group of people who remained healthy after being exposed to the coronavirus on the Diamond Princess are tested for natural antibodies, that information could allow scientists the opportunity to understand more about how it spreads and how to fight it. 

"This gives us a discrete pool of people that we can pull from," said Mina. "And so we could learn a lot from that type of study, to really understand how widely this is transmitting without symptoms."