Thread by @inkblue01

A lookback thread on the Princess Diamond Cruise that was docked in Yokohama, Japan in Feb of 2020. Of the 3,711 people on board, 712 became infected with the virus – 567 of 2,666 passengers, and 145 of 1,045 crew, 14 deceased or 2% CFR🧵1/13

An 80-year-old passenger from Hong Kong, China, developed a cough on January 19th. He left the cruise when the ship reached Hong Kong on 25 January. 2/

Feb 1, the 80-year-old man who disembarked in Hong Kong six days earlier tested positive for COVID-19. Having a fever, he went to the hospital and got tested. 3/

On 4 February, tests onboard revealed infections of 10 out of 31 people tested. The authorities immediately decided to isolate all passengers on board for 14 day. A total of 3,700 passengers and crew were quarantined for 14-day period, off Yokohama. 4/

By Feb 14th the total case count on board was 542. On 19 February, passengers with negative test results began to disembark. By late March, it was stated that 712 of 3,711 people on the Diamond Princess, or 19.2%, had been infected by COVID-19. 5/

There are many criticisms of Japan's epidemic prevention measures of quarantine on cruise ships. There is the possibility that quarantine in a cruise ship is dangerous, because the cruise ship does not use HEPA filters which can effectively screen 99 percent of the particles. 6/

Kentaro Iwata, an infectious diseases expert at Kobe University who visited the ship, strongly criticised the management of the situation. He said that the areas possibly contaminated by the virus were not in any way separated from virus-free areas...7/

there were numerous lapses in infection control measures, and that there was no professional in charge of infection prevention—the bureaucrats were in charge of everything 8/

Food service workers were found to have likely been the main early route of spread. 46.5% of the infected passengers and crew members had no symptoms at the time of testing. The ship outbreak had a basic reproduction number of 14.8 much higher than the usual 2–4. 9/

Calculations indicate that an early evacuation could have reduced the case number to just 76 cases, and that the applied quarantine reduced the case number by about 2300 cases. 10/

Those infected got CT scans even asymptomatic and mild symptoms at the SDF Central Hospital, and half of them were found to be abnormalities. Their CT images showed a frosted glass-like shadow, a feature of the new coronavirus pneumonia. 11/

About one-third of patients with abnormal shadows in the lungs subsequently had worsening symptoms. They often started to get worse on the 7th to 10th day of their first symptoms, which progressed relatively slowly. 12/

Airborne transmission likely accounted for >50% of disease transmission on the Diamond Princess cruise ship, which includes inhalation of aerosols during close contact as well as longer range. /end
en.wikipedia.org/wiki/COVID-19_…