Explained: Why cruise ships are especially vulnerable during outbreaks of disease

Passengers stand on the balcony of the cruise ship Diamond Princess anchored at the Yokohama Port in Yokohama, near Tokyo Friday, Feb. 7, 2020. (AP Photo: Eugene Hoshiko)

The cruise ship Diamond Princess, which has been quarantined in Japan’s Yokohama for two weeks amid the novel coronavirus outbreak, has 3,700 people on board including several Indians. The Japanese government said Saturday at least 64 people on board had tested positive for the virus.

The ship, which left a Hong Kong port on January 25, has been quarantined for 14 days after a person who disembarked in Hong Kong was found to have been infected by the virus.

External Affairs Minister S Jaishankar confirmed Friday that many Indians were on board the ship. “Many Indian crew and some Indian passengers are onboard the cruise ship #DiamondPrincess quarantined off Japan due to #Coronavirus. None have tested positive, as per the latest information provided by our Embassy,” he tweeted.

Coronavirus has so far claimed the lives of over 750 people, while more than 31,000 people have been infected.

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Why do ships become vulnerable during outbreaks of disease?

According to the Centre for Disease Control and Prevention (CDCP), cruise ships may be especially vulnerable to communicable disease outbreaks because travelers from diverse regions are brought together in an environment that is “often crowded” and semi-closed. Such conditions facilitate the spread of person-to-person, foodborne or waterborne diseases.

Further, diseases can be sustained for multiple voyages by transmission among crew members if the environment remains contaminated or if the crew remains on board.

A passenger wearing a face mask stretches in his cabin on the cruise ship Diamond Princess. (Reuters Photo: Kim Kyung-Hoon)

A 2009 article published in Clinical Microbiology says the following about the spread of communicable diseases onboard cruise ships: “The closed environment aboard cruise ships, close contact among passengers and crew, and common sources of food and water provide ample opportunity for exposure to and transmission of infectious diseases. Of these, gastrointestinal and respiratory infections pose the greatest risk of outbreaks. Outbreaks on cruise ships present a public health concern, since infection is often easily spread, is difficult to control, and has the potential to disseminate pathogens.”

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Significantly, the WHO, in its Handbook for management of public health events on board ships, has said that in the past centuries, infectious diseases have spread to non-affected countries through ships. They continue to play a role in the transnational dispersal of vectors and, in recent years, the dispersal of “harmful aquatic organisms and pathogens as well.”

Workers wearing protective gear prepare to transfer passengers who tested positive for coronavirus from the cruise ship Diamond Princess to an ambulance bound for the hospital. (Reuters Photo: Kim Kyung-Hoon)

In the case of the novel coronavirus, the infection can spread from person-to-person when in close contact (about 6 feet). Person-to-person transmission can occur through respiratory droplets, which are produced when an infected person coughs or sneezes. The infection enters the body through ones mouth or nose and can even be inhaled into the lungs.

It is not clear if a person can be infected by touching the surface that has the virus on it and subsequently touching his own nose, mouth or eyes.

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In an announcement, the captain of Diamond Princess Friday said, “Quarantine officials require that you avoid congregating in large groups and maintain separation of at least one metre from each other when talking… We require that you wear as a minimum, warm clothing, hat and a scarf if possible.”