Dr. Todd Kenyon looks at the data from the situation onboard the Diamond Princess early in the pandemic:
Diamond Princess is a cruise ship owned and operated by Princess Cruises. She began operation in March 2004 and primarily cruises in Alaska during the summer and Asia in the winter along with Australia cruises. Diamond Princess and Sapphire Princess were both were built in Nagasaki, Japan by Mitsubishi Heavy Industries.
Photo by Bernard Spragg, NZ via Wikimedia Commons.
The Diamond Princess cruise ship departed Japan on January 20, 2020. Five days later a passenger disembarked, later became ill and tested positive for SARS-CoV-2 infection. On board this ship were 3,711 persons, of which 2,666 were passengers (median age of 69) and 1,045 were crew (median age of 36). Nearly half (48%) of the passengers were said to have underlying disease(s). Passengers and crew began testing positive with some becoming ill, but the passengers were not quarantined in their cabins until Feb 5. Until that time they had been engaging in a variety of typical social activities including shows, buffets and dances. Once quarantined (confined to cabins), most passengers shared cabins with 1 to 3 other passengers. Cabins used unfiltered ventilation and the crew continued their duties and mixed with passengers. Evacuation began in mid February and was completed by March 1.
A total of 712 individuals (19%) tested positive via PCR, and as many as 14 passengers were said to have died, though there are differing opinions as to how many of these deaths should be attributed to Covid. Except for one person in their late 60s, all deaths occurred in those over 70. Not one crew member died. Half of the deaths occurred several weeks after leaving the ship, so it is unclear if they actually died from infections caught onboard. Three ill passengers were given an experimental treatment of Remdesivir once hospitalised on shore; apparently all survived.
The Diamond Princess was termed a “virus mill” by one expert while another remarked that cruise ships are perfect environments for the propagation and spread of viruses. The quarantine procedures inflicted much duress on an already frail passenger base and may have done more harm than good. There was panic and confusion both among passengers and crew, and densely packed passengers sharing unfiltered ventilation were only allowed out of cabins every few days for an hour. Meanwhile the crew continued to prepare meals and mix with passengers, but otherwise were kept confined below the waterline in their cramped multi-resident quarters. Some passengers ignored the quarantine entirely. The so-called “Red Dawn” email discussions among government researchers in early 2020 described the DP as a “quarantine nightmare”. The DP was also termed by this group as representative of a large elderly care home (passengers). Based on all these observations, the DP event should provide a nearly worst case scenario for the first wave of Covid. The question is, how did New York City (NYC) fare versus this “worst case”, and what can we learn from the comparison?
We can start by looking at the infection rate on the DP: 25% of those over 60 and 9% of those under 60 were reportedly infected. On the DP, the case fatality rate (CFR) for those over 60 was 2.6%. This assumes that all 14 deaths of passengers were caused by a Covid-19 infection contracted while on the DP. On the other hand, the CFR for those under 60 years of age was 0.0%, since none in this age bracket died.
Diamond Princess mortality (scaled) compared to New York City all cause mortality. DP week 1 = first week quarantine imposed while NYC week 1 = first week of lockdown orders (week 12, 2020). DP fatalities are scaled based on relative populations of individuals over 65. It is unclear whether the DP fatalities at the tail end of the curve are attributable to C19 infection contracted months prior on the DP. NYC data: www.mortality.watch
