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

  1. Pengcheng Xu
  2. Hua Qian
  3. Te Miao
  4. Hui-Ling Yen
  5. Hongwei Tan
  6. Min Kang
  7. Benjamin J. Cowling
  8. Yuguo Li

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Abstract

Background

An outbreak of COVID-19 occurred on the Diamond Princess cruise ship in January and February 2020. We analysed information about cases to infer transmission dynamics and potential modes of transmission.

Methods

We collected the daily number of 197 symptomatic cases, and that of the 146 passenger cases in two categories, i.e. those who stayed and did not stay in the same stateroom. We retrieved the quarantine details and the ship’s 14-day itinerary. We searched the websites of national/local health authority along the cruise routes and local news using Google for locally confirmed cases associated with the ship. We obtained the design of air conditioning and sewage treatment of the ship from literature. We back-calculated the dates of infection from the epidemic curve and compared with the start of on-board quarantine.

Results

Major infections started on Jan 28 and completed by Feb 6 for passengers except those who stayed in the same stateroom with infected individual(s). No other confirmed cases were identified among the disembarked people in Hong Kong except an 80 years old passenger. No confirmed cases were reported in three other stopovers between Jan 27-31 associated with disembarked passengers or visitors from the ship, however two Okinawa taxi drivers became confirmed cases in association with driving the ship passengers. Infection among passengers after Feb 6 was limited to those who stayed in the same stateroom with an infected passenger. Infections in crew members peaked on Feb 7, suggesting significant transmission among crew members after quarantine on Feb 5.

Conclusions

We infer that the ship central air conditioning system did not play a role, i.e. the long-range airborne route was absent in the outbreak. Most transmission appears to have occurred through close contact and fomites.

Significance Statement

Transmission by the long-range airborne route for SARS-CoV-2 in the 2020 Diamond Princess Covid-19 outbreak has been debated with significant implication for intervention. We found that the transmission by close contact and fomite explains the outbreak, and the central air-conditioning system did not play a role, demonstrating the importance of social distancing, good hygiene and maintaining good building ventilation for intervention.

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    SciScore for 10.1101/2020.04.09.20059113: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Our estimation method is not without limitations. We cannot rule out the possibility of other infections during later part of the quarantine period due to incomplete data. Among the 634 cases confirmed by Feb 20, though 328 were asymptomatic, 306 were symptomatic at the time of confirmation. However, only 197 of the 306 symptomatic individuals had onset date, and further data from the remaining 109 symptomatic individuals may change our prediction. Our predicted data also did not include possible transmission between crew and passengers prior to and during the quarantine period as they come into contact with each other, such as serving meals. We used the estimated incubation period from 186 patients in China, with known dates of both infection and onset of symptoms. The governing equation is known to be ill-posed, and assumptions were made (see Methods section, and also Li et al, 2005), though our method successfully predicted all seven reported super spreading events in the 2003 SARS epidemics in Hong Kong and Singapore. Figure S1 also showed that we also successfully predicted in the infection date for the 186 patients. Lastly, our approach cannot be used to study the roles of the asymptomatic cases in the transmission. The asymptomatic cases were first detected on the ship when the tests were extended to all passengers on Feb 15 after focusing in those with symptoms (Wikipedia, 2020). If the spatial distribution (room where the confirmed case stayed) of both symptomatic an...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

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  2. Version published to 10.1101/2020.04.09.20059113v1 on medRxiv