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Transmission routes of COVID-19 virus in the Diamond Princess Cruise ship

Our take —

This study, available as a preprint and thus not yet peer reviewed, leveraged multiple data sources to assess transmission dynamics among a subset of symptomatic cases on the Diamond Princess Cruise Ship from January 20 to February 18, 2020. Results suggest that close contact and fomite (e.g., hand-to-inanimate-object-to-nose) transmission routes were primarily responsible for the outbreak, and that airborne transmission did not appear to occur. This study used data from a subset of symptomatic cases only and did not account for transmission via asymptomatic cases. It may therefore be subject to both selection bias and insufficient assessment of transmission pathways.

Study design

Other

Study population and setting

Data analyzed in this study included 197 symptomatic cases detected among passengers and crew on the Princess Diamond Cruise Ship in Japan from January 20 to February 18, 2020. Passengers were defined as close contacts if they stayed in a cabin room with a COVID-19 case, and as non-close contact or other passengers if they stayed in a cabin room without a COVID-19 case. Multiple data sources on cases, interaction between individuals, ship design, and implementation strategies were used to estimate the periods of infections, as well as understand transmission dynamics, such as differences in transmission patterns between close contact and non-close contact individuals, and the potential role of the ship’s central ventilation systems.

Summary of Main Findings

Authors estimated the greatest number of identified symptomatic infections occurred two days prior to the implementation of quarantine. After quarantine, when passengers were limited to their living quarters, infections were limited to those staying in the same room as another infected individual. Authors suggest that these findings are indicative of transmission via fomite and close contact routes.

Study Strengths

This study leveraged multiple data sources, including symptomatic cases, ship design, quarantine implementation strategies, and passenger contact to assess and understand transmission dynamics.

Limitations

This study used data on symptomatic cases with the date of symptom onset available, which limited the data to approximately two-thirds of symptomatic cases (due to missing data and all asymptomatic infections). Therefore, results may be subject to selection bias and may insufficiently consider transmission by asymptomatic cases. The study did not provide a detailed spatial analysis, which could have been useful in understanding clustering of cases. Authors suggest fomite transmission played a role in the outbreak, however, very little evidence is offered to support this transmission route other than references to similar routes of transmission during norovirus outbreaks.

Value added

This study found no evidence for long-range airborne transmission of SARS-CoV-2 through the central ventilation system on the Diamond Princess cruise ship. Instead, authors suggest that close contact and fomite transmission routes were primarily responsible for the outbreak.

This review was posted on: 21 July 2020