Diamond Princess epidemics of COVID-19

The Diamond Princess, with more than 3700 people on-board, has been in quarantine at the port of Yokohama for nearly two weeks. The New York Timesdescribed the Diamond Princess as “a floating, mini version of Wuhan”.

Diamond Princess was carrying 2,666 passengers and 1,045 crew from a range of nationalities when it arrived at Yokohama on Feb 3. About half the passengers are from Japan. Local health authorities undertook screenings and ordered the quarantine after a man on the prior sailing was later diagnosed with 2019-nCoV in HK. As of Feb 21, 2020, 691 cases have been confirmed amongst those on board.  By 27 February, at least 150 of the crew members had tested positive for the virus

When the Diamond Princess left the port of Yokohama in Japan on January 20, the 2,666 passengers on board were ready to unwind with a trip to China, Vietnam and Taiwan. But two weeks later they’d find themselves confined to their cabins, allowed out for only a few hours each day, while 542 of their fellow passengers and crew tested positive for Covid-19 – the novel virus that has infected 75,000 people worldwide.

While the Covid-19 outbreak has been slow to take hold outside of China, the Diamond Princess has been a hotspot of infection. Of all the confirmed cases outside of China, more than half of them were on the cruise ship. Singapore, the country with the next-highest number of cases, has just 77 confirmed infections. This is how a pleasure trip in east Asia turned into a battleground in the fight against a deadly epidemic.

For more than two weeks, the passengers of the Diamond Princess have swapped three-course dinners for boxed meals doled out three times a day by crew in masks and gloves, prepared by a temporary kitchen set up on shore by a charity that normally supplies meals during natural disasters. The casino is shut, but the creaky Wi-Fi remains available, and Amazon deliveries are reportedly making it on board, although the alcohol started to run out midway through the quarantine.

While the official quarantine is set to end on February 19, most of the passengers will require further patience as they face a further two weeks in isolation when they return to their home countries – and for those unlucky enough to catch Covid-19, a stint in hospital.

On February 1, a passenger who had disembarked five days earlier in Hong Kong was diagnosed with Covid-19. The ship's voyage was paused on February 4 by health authorities for 24 hours for a health check, but Princess Cruises quickly cancelled the entire trip, docking in Yokohama to give more time to check passengers and crew. Ten passengers were found to be infected, and taken ashore for medical treatment.

Two days later, the number of infected had risen to 41, but the Japanese Ministry of Health believed at the time no further tests were required. The remaining passengers were asked to quarantine on board, with the cruise company offering free internet access, switching on additional satellite TV channels, and offering those in rooms without any windows a chance to get a breath of fresh air on deck now and then. Passengers tweeted photos of flowers, chocolates and other gifts handed out by staff, including games and cards for children.

"We hope these gestures will lift the spirits of those onboard in this difficult time," said Rai Caluori, EVP at Princess Cruises, in a written update at the time. Official updates were shared via notes printed out and slid under cabin doors, while passengers left thank-you messages for crew pinned to their doors, but also turned to social media to share their boredom, frustration, and anxiety.

On February 8, another six cases were found, and a day later, a further 66. Princess Cruises told passengers it will refund all their costs, including air travel, not charge for anything onboard during the lockdown, and offer a free cruise in the future — should anyone want to take that up. The cruise company also offered passengers the option to complete their quarantine at a shoreside location, but stressed they had no medical staff and all food would be Japanese style bento boxes; those who do disembark are tested for the virus first.

Shortly after, the US announced it would repatriate American passengers; one passenger who opted to remain on board reported hearing chants of "USA!" and "get me off this ship" when their departure came. Infections continued to pile up, with 169 new cases the day before quarantine was supposed to end.

An Australian doctor, tweeting about her parents quarantined on board, said: "He was tested and negative upon confinement but now positive. Confinement isn’t working."

In total, 542 people have been infected with the illness, despite the lockdown on-board. Does that mean the quarantine didn't work? "The primary reason for the quarantine was to stop potentially infectious people then spreading infection further around the world as they continued their holidays or returned home. In this regard it would appear that the quarantine has so far been successful," says Paul Hunter, professor in medicine at the University of East Anglia, in a statement provided by the Science Media Centre.

The Westerdam cruise ship docked in Cambodia to allow passengers to disembark; it was only after they'd scattered home that an infection was spotted. On board the Diamond Princess, the virus didn’t have so far to travel. "With the high number of cases reported in the past few days it would appear that measures to prevent spread amongst passengers and crew after quarantine was imposed were ineffective," Hunter says.

Those stuck on the luxury cruiseliner won't want to hear that – especially Britons like David and Sally Abel, who have used YouTube videos and Facebook to call on the government to charter an evacuation flight; the couple have now tested positive for coronavirus. Now, the British Foreign Office has said:

“Given the conditions onboard, we are working to organize a flight back to the UK for British nationals on the Diamond Princess as soon as possible."

There are three ways the quarantine could have failed those onboard, says Bahrat Pankhania, public health lecturer at the University of Exeter. First, some people may have been exposed to the virus before the ship was locked down – after all, there was at least one sick passenger who disembarked in Hong Kong, and ten more a few days later. "Then slowly over a period of time they became infected," Pankhania suggests.

The second option is that the virus has spread despite the quarantine.

Given the precautions, such as passengers keeping to cabins, staff delivering meals wearing masks, this would hopefully be unlikely, but most of the 1,045 crew share bedrooms and tables of 14 for meals – with Princess Cruises only asking them to leave a seat between them ten days into the two-week quarantine, according to one report from Time.

One crew member who developed a fever was told to stop work and self-isolate in their cabin – which they shared with another member of crew, who continued to work. The roommate has since tested positive for coronavirus.

The spread could be exacerbated by passengers not following rules. The chants of "USA!" allegedly came from a woman standing on her balcony, not wearing a mask despite talking to a passenger on an adjacent balcony a few feet away, reported another passenger, Matthew Smith. "If there are secondary infections onboard, this is why: idiots who don't know any better," he said on Twitter.

There's a third route for infection that is concerning, which Pankhania says has precedent but remains a theory: the air conditioning system linking cabins. That idea was explored after the Sars outbreak, with researchers trying to account for how the disease spread between people without direct contact in one hotel. "An infection occurred which moved from the bottom of the building to a distant part of the building via the air conditioning system, infecting people very distant from each other," he says.

There are a few caveats, complicated by the fact there's plenty we still don't know about this novel coronavirus. So far, Sars-CoV-2 appears to travel via droplets – what's expelled from your face when you cough or sneeze – which is why authorities are working on the assumption that you need "close contact" to spread the virus, which means being within two meters of someone for 15 minutes. For example, one infected woman took a five-minute Uber trip to the hospital, but the driver shouldn't be at risk.

And that may still be the case with this scenario. Because the cabins are small and passengers are spending all their time in them, even a tiny amount of the virus in the room could equate to prolonged exposure. "People are cooped up in cabins that are very small, with not a lot of air movement, especially if you've adopted the lock down instructions," he says. "The only exchange of fresh air is the air conditioning systems that do not necessarily have proper filters."

While evacuation may be welcome to passengers, Pankhania warns that filling a hotel with potentially infected travellers has the same risks as the ship – they too can have weaknesses in quarantine and also feature air conditioning.

Because of that, he says that anyone at serious risk of infection, such as those on the ship who may have been exposed for a long time, should be more carefully watched for symptoms. If they develop, they should not be allowed to stay in the hotel, but taken to hospital, to avoid infecting others. "Being in the hotel is the same as being on a ship, to be honest – the room is a little bigger," he says.

The cause of the continuing outbreak on the Diamond Princess could be any of those options – or all three at once. One as yet unanswered question is why passengers would be quarantined on a cruise ship, notorious as they are for spreading disease. Data from the US Centre for Disease Control shows ten outbreaks on cruise ships last year, eight of which were norovirus. “Cruise ships are very prone to outbreaks of common cold and the vomiting virus, norovirus," notes John Oxford, professor of virology at Queen Mary University, London, in a statement from the Science Media Centre. "Invariably the ships are overcrowded and with so many passengers hygiene levels can slip… In fact it might be impossible to properly quarantine people on a ship. I am sure that passengers will need to be quarantined properly when they return home."

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2020 coronavirus outbreak on cruise ships - Wikipedia