COVID-19: Transmission aboard the Diamond Princess cruise ship

 COVID-19: Transmission aboard the Diamond Princess cruise ship. Jefferson T,  Heneghan C.

Published on June 18, 2020

Reference Kakimoto K, Kamiya H, Yamagishi T, Matsui T, Suzuki M, Wakita T Investigation of Transmission of COVID-19 Among Crew Members During Quarantine of a Cruise Ship — Yokohama, Japan MMWR Morb Mortal Wkly Rep 2020;69:312-313.
Study type
Country International waters and Yokohama, Japan
Setting Cruise Ship
Funding Details MMWR and Morbidity and Mortality Weekly Report are service marks of the U.S. Department of Health and Human Services.
Transmission mode Close contact, Person to person, Fomite
Exposures Cruise Ship, passenger turnover

Bottom Line

Swift action by diagnosis, testing, contact-tracing and isolation would have probably avoided the majority of 619 cases aboard. 

Evidence Summary

Two cases in passengers infected other passengers and ultimately some service crew members (6% of the crew) who served food in their cabins. As these messed with other crewmembers, they infected some and those whose accommodation deck they shared.

The crew dining area was the primary area of congregation; passengers did not access this part of the ship.

  • 15/20 confirmed cases in crew members occurred among food service workers
  • 16/20 cases occurred among those with cabins on deck 3, the deck on which the food service workers lived

Delay in diagnosing, contact tracing and isolation probably facilitated transmission which the authors hypothesise as being by contact and droplet. 

What did they do?

There are two papers on the Diamond Princess outbreak. The first by Kakimoto is a preliminary report of the investigation carried out onboard the cruise ship Diamond Princess when docked at Yokohama, Japan. The second is a model estimating IFRs, with inference from the epidemiological characteristics of the ship outbreak to the population of China (not discussed)
Japanese public health officials investigated the ship outbreak with a combination of enquiry, testing and follow-up. 

Study reliability

The preliminary report is unclear as to the actual potential contact between food service crew members and quarantined passengers. Followup of passengers and crew beyond the end of February is unclear.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes No No Partly No

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Tom Jefferson

Tom Jefferson, epidemiologist.