Diamond Princess quarantine. What went wrong?

Despite claims by Japanese authorities that the quarantining of cruise ship Diamond Princess off Yokohama for more than two weeks had been the right thing to do and had been administered correctly, many scientists, in cluding a Japanese health expert, have said that it was a failed experiment.

Having been isolated because a single passenger who had already disembarked had becoming infected with the Covid-19 virus, the following two weeks saw more than 600 people test positive, a solid indicator that the virus was continuing to spread.

Notwithstanding this, Japan appeared to decide on Wednesday this week that any Japanese not testing positive for the virus were free to go home. Some of them were seen departing on buses and in taxis.

On Thursday February 20th it emerged that two of the infected passengers – both of them in their 80s and with underlying health conditions – had died. More than 20 remain in serious condition.

Five Japanese health officials who helped conduct the quarantine checks on the ship were also infected, including one health ministry official and another from the Cabinet Secretariat, who on Thursday this week were confirmed to have the virus.

Michael Ryan, executive director of the World Health Organization’s health emergencies programme, said that “there are sometimes environments in which disease can spread in a more efficient way”. Dr Ryan said cruise ships in particular were known occasionally to accelerate spread. “It’s an unfortunate event occurring on the ship and we trust that the authorities in Japan and the governments who are taking back people will be able to follow up those individuals in the appropriate way,” Dr Ryan said.

Nathalie MacDermott, an outbreak expert at King’s College London, said that “obviously the quarantine hasn’t worked, and this ship has now become a source of infection”.

Scientists believe the disease is spread mostly by droplets, through coughs and sneezes, but it was possible there were other ways of transmission. Br MacDermott said that “we need to understand how the quarantine measures on board were implemented, what the air filtration on board is like, how the cabins are connected and how waste products are disposed of. There could also be another mode of transmission we are not familiar with”. Dr MacDermott emphasized the importance of deep-cleaning the entire ship to prevent people from touching contaminated surfaces.

She added that there was no reason the quarantine should not have worked if it had been done properly, while noting that it was highly unusual for an entire boat to be quarantined. “They might quarantine the people affected in their rooms until they’re 48 hours clear of symptoms, but certainly not all passengers”. In other words, the isolation of an entire ship was something of an unknown territory for the Japanese health authorities.

Paul Hunter, a professor of medicine at the University of East Anglia, told ABC News that “I suspect people were not as isolated from other people as we would have thought,”  and that the continued spread of the virus could be due to compliance problems. “It’s difficult to enforce a quarantine in a ship environment and I’m absolutely sure there were some passengers who think they’re not going to let anyone tell them what they can and cannot do”.

Dr Hunter said that if the passengers had been quarantined on land, having more space might have allowed for better infection control procedures. However,  he acknowledged that attempting to quarantine more than 3,700 people was logistically challenging.

Dr Hunter said that “given how the virus has continued to spread, we have to presume everyone leaving the ship is potentially infected, and therefore they have to go through another two-week quarantine period. Not to do so would be reckless.”

The quarantine was largely for passengers because crew members kept sharing double rooms and continued to serve guests by delivering food, letters, towels and amenities, and entering passenger cabins for cleaning. Crew members also ate in groups in a crew mess hall.

The virus has already made its way into local communities across Japan, where untraceable cases have been appearing.