News & Information Blog

Case Study of the Diamond Princess Coronavirus Outbreak

By Susen Trail | 03/23/2020

On January 21,2020 an 80 year old Hong Kong man came aboard the Diamond Princess, a cruise ship, and he disembarked on January 26th.  On February 1, 2020 he tested positive for COVID-19.  On February 3rd the Diamond Princess docked in Japan’s Yokohama port and the Japanese government started testing the people on the ship.  On February 4th 10 of the tests came back positive for COVID-19 and the ship was put under quarantine for 14 days. 

However, there was no real preparation between the government and the cruise line to create a clear and a contaminated zone and several other serious inadequacies that created a worst-case exposure scenario for the 3,711 guests and crew on the ship. 

For a detailed description of conditions on the ship I recommend watching the YouTube video made by a member of the medical relief team, Kentaro Iwata, an infectious diseases expert at Kobe University Hospital.

Conditions conducive to increasing the spread of disease on the ship:

  1. Confined all passengers to their rooms but did not do anything to the ventilation system, which was not effective in removing virus particles and did not provide 100% outside air to each room.
  2. Allowed staff, including those testing positive and those actively ill, to eat together and sleep in quarters where they could spread the infection amongst themselves. Then had them prepare and deliver food. 
  3. Did not instruct, or did not enforce, staff to use the PPE provided properly. Instagram pictures showed crew delivering food with one of the respirator straps hanging under his chin.
  4. Pictures show passengers lining up for testing without face masks or gloves, so they were exposed to infected passengers and touching potentially contaminated surfaces at the testing site as well as from and to their rooms.

What can we learn from this?  Of the 3,700 people only 707 people test positive on the ship that is only 19% of the people on board.  This is not what you would expect from a highly contagious disease with people living in close quarters for 14 days.  

The population on the boat has not been broken down by age group in any documentation I can find.  Of the 6 people from the ship that died 2 were 80 years old, one was 87, one was 84, one was in her 70’s, and I could not find the age of the 6th person.  Which gives us a 0.8% mortality rate.  While this IS higher than the average seasonal influenza rate, 0.1%, it is much less than the last SARS outbreak which took 2% of those infected. 

Comorbidities are preexisting conditions that make the patient more likely to contract the disease and/or more likely to have a more severe reaction.  Comorbidities for corona viruses include:

  • History of smoking
  • Bacterial co-infection
  • High blood pressure
  • 60 or more years old
  • Cardiac issues
  • Diabetes
  • Hepatitis
  • Pneumonia

The following reasons indicate that COVID-19 virus may be less dire then it seems right now.

  1. Most of the people infected develop mild symptoms and may not even go to the doctor. Since they won’t be counted it artificially increases the mortality rate.  This is not true for the statistics from the cruise, where everyone was tested.
  2. Like the flu, the elderly, immune compromised, and people with an underlying medical condition such as a history of cardiac or respiratory problems, are the hardest hit.
  3. Given national and international travel that occurred before countries started limiting incoming flights, it is most likely that there are a great many cases that have already come and gone. This means that the denominator, identified population infected, will continue to grow at a rate much faster than the number of fatalities. 

An article in the New England Journal of Medicine states “If one assumes that the number of asymptomatic or minimally symptomatic cases is several times as high as the number of reported cases, the case fatality rate may be considerably less than 1%.” 

For a more in-depth article on infectious viruses click here.

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