Epidemiology of COVID-19 Outbreak on Cruise Ship Quarantined at Yokohama, Japan, February 2020

Abstract

To improve understanding of coronavirus disease (COVID-19), we assessed the epidemiology of an outbreak on a cruise ship, February 5-24, 2020. The study population included persons on board on February 3 (2,666 passengers, 1,045 crew). Passengers had a mean age of 66.1 years and were 55% female; crew had a mean age of 36.6 years and were 81% male. Of passengers, 544 (20.4%) were infected, 314 (57.7%) asymptomatic. Attack rates were highest in 4-person cabins (30.0%; n = 18). Of crew, 143 (13.7%) were infected, 64 (44.8%) asymptomatic. Passenger cases peaked February 7, and 35 had onset before quarantine. Crew cases peaked on February 11 and 13. The median serial interval between cases in the same cabin was 2 days. This study shows that severe acute respiratory syndrome coronavirus 2 is infectious in closed settings, that subclinical infection is common, and that close contact is key for transmission.

Keywords: 2019 novel coronavirus disease; COVID-19; Japan; SARS-CoV-2; coronavirus disease; cruise ship; epidemiology; quarantine; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Number of coronavirus disease cases aboard cruise ship quarantined in Japan, by date of symptom onset, February 5–20, 2020 (n = 178). The graph displays the number of cases by symptom onset date for the cases for which onset date was available for passengers and crew members. Cases without a recorded symptom onset date were excluded.

Figure 2

Spatial mapping of coronavirus disease cases aboard cruise ship quarantined in Japan, by deck, February 3–25, 2020. The ship had 18 decks (i.e., floors). Decks 4–14 contained cabin rooms for passengers; decks 2 and 3 were for crew. Red dots indicate the latest cases in cabins (i.e., cases with illness onset starting February 13–16 or infected but asymptomatic persons whose samples tested positive by real-time reverse transcription PCR from February 16 onward. Orange dots represent cases in passengers or crew who appeared to be infected before those periods.