The virus was identified before disinfection procedures had been conducted, but it is still uncertain whether transmission occurred from contaminated surfaces, the data by Takuya Yamagishi, National Institute of Infectious Diseases, shows.

On January 20, the Diamond Princess cruise ship departed Yokohama, Japan, carrying approximately 3,700 passengers and crew.

On January 25, a symptomatic passenger departed the ship in Hong Kong, where he was evaluated; testing confirmed SARS-CoV-2 infection.

On February 3, the ship returned to Japan, after making six stops in three countries. Japanese authorities were notified of the COVID-19 diagnosis in the passenger who disembarked in Hong Kong, and the ship was quarantined.

On February 5, passengers were quarantined in their cabins.

Initially, travelers with fever or respiratory symptoms and their close contacts were tested for SARS-CoV-2 by reverse transcription–polymerase chain reaction (RT-PCR). All those with positive test results were disembarked and hospitalized.

Testing was later expanded to support a phased disembarkation of passengers, prioritizing testing of older persons, those with underlying medical conditions, and those in internal cabins with no access to the outdoors.

During February 16–23, nearly 1,000 persons were repatriated by air to their home countries. The remaining passengers who had negative SARS-CoV-2 RT-PCR test results, no respiratory symptoms, and no close contact with a person with a confirmed case of COVID-19 completed a 14-day ship-based quarantine before disembarkation.

Those passengers who had close contact with a person with a confirmed case completed land-based quarantine, with duration determined by date of last contact.

After disembarkation of all passengers, crew members either completed a 14-day ship-based quarantine, were repatriated to and managed in their home country, or completed a 14-day land-based quarantine in Japan.

Among 3,711 Diamond Princess passengers and crew, 712 (19.2%) had positive test results for COVID-19.

The Diamond Princess and Grand Princess had more than 800 total COVID-19 cases, including 10 deaths.