Diamond Princess had coronavirus traces 17 days after passengers left cruise ship: CDC
Among the 428 American passengers and crew members who were quarantined, 107 tested positive and 11 were hospitalized in Japan as of March 13
The new coronavirus left a part of it behind on the infamous Diamond Princess cruise ship. The virus stayed put in the cruise ship cabins for up to 17 days after the passengers vacated the ship, according to a Centers for Disease Control and Prevention (CDC) report.
Though the report does not explain whether this led to an increased number of infections, it does paint a detailed picture of how the virus spread on the ship. It also talks about the vulnerability of cruise ships, including the Grand Princess.
Overall, both the Diamond Princess and Grand Princess confirmed more than 800 positive cases for COVID-19 and 10 deaths.
Between February 3 and March 13, 200 Americans contracted the disease on cruise ships. This accounted for about 17% of the total reported US cases at the time.
"During the initial stages of the COVID-19 pandemic, the Diamond Princess was the setting of the largest outbreak outside mainland China. Many other cruise ships have since been implicated in SARS-CoV-2 transmission," the report said. Twenty-five other cruise ships have confirmed COVID-19 cases since.
The Diamond Princess cruise ship debacle
Fearing that people on the ship could pass on the virus to others in the country, the Japanese government sealed the ship off for 14 days.
Experts soon called out this measure as unethical. "They’ve trapped a bunch of people in a large container with (the) virus. So (I'm) assuming 'quarantine' is generating active transmission," University of Toronto epidemiology professor David Fisman, told Vox.
And they were right. According to the report, among 3,711 people, 712 tested positive. Of them, 331 did not show symptoms at the time of testing. However, the report does not mention whether this group developed symptoms later.
"They didn't report a follow-up to show how many eventually developed symptoms," tweeted infectious disease expert Tara C Smith.
As for the rest who showed symptoms at the time of testing, 37 people needed intensive care and nine died.
Among the 428 American passengers and crew members who were quarantined, 107 tested positive and 11 passengers were hospitalized in Japan as of March 13, according to the report.
The authors of the report attribute the rapid spread of the virus to patients who did not show symptoms at that time. Besides, scientists had earlier predicted that about 18% of infected people never developed symptoms.
Further, scientists examined the surfaces of the cabins occupied by infected patients — both with and without symptoms. The team found the genetic material or RNA of the virus on a variety of surfaces in cabins of all the infected patients for up to 17 days after the passengers left.
This, however, does not prove that the virus was spreading through contaminated surfaces. The authors call for more studies that can investigate this.
What did the Japanese investigation say?
An early Japanese investigation revealed that the passengers were the first to get sick. The crew caught the infection while interacting with the passengers.
"COVID-19 was likely transmitted first from passengers to crew members and subsequently spread among the crew, especially among food service workers. The first case detected in a crew member occurred in a food service worker who developed a fever on February 2," the report said.
Their analysis also found that the spread to the crew happened before the start of the quarantine.
What about Grand Princess?
The Grand Princess was an example of how the virus spreads from crew members across multiple consecutive voyages, the authors note in their report.
This cruise ship hosted 3,571 passengers. Two passengers from the first voyage in February tested positive after leaving the ship and one died. The CDC alerted the ship about these developments while it was on its second voyage. Most of the 1,111 crew and 68 passengers from voyage A remained on board for a second voyage that departed San Francisco on February 21.
But the CDC did not repeat the mistakes committed on Diamond Princess. After docking in Oakland, California, on March 8, passengers and crew were quarantined on land for 14 days. As of March 21, of the 469 quarantined Americans, 78 tested positive.
The authors conclude that the virus can exploit the proximity provided by cruise ships. "Outbreaks of COVID-19 on cruise ships pose a risk for the rapid spread of disease beyond the voyage. Aggressive efforts are required to contain the spread. All persons should defer all cruise travel worldwide during the COVID-19 pandemic," they wrote.