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. 2021 Mar 16;16(3):e0248273.
doi: 10.1371/journal.pone.0248273. eCollection 2021.

Taking account of asymptomatic infections: A modeling study of the COVID-19 outbreak on the Diamond Princess cruise ship

Li-Shan Huang  1 , Li Li  2 , Lucia Dunn  3 , Mai He  4
Affiliations

Taking account of asymptomatic infections: A modeling study of the COVID-19 outbreak on the Diamond Princess cruise ship

Li-Shan Huang et al. PLoS One. .

Abstract

The COVID-19 outbreak on the Diamond Princess (DP) cruise ship has provided empirical data to study the transmission potential of COVID-19 with the presence of pre/asymptomatic cases. We studied the changes in R0 on DP from January 21 to February 19, 2020 based on chain binomial models under two scenarios: no quarantine assuming a random mixing condition, and quarantine of passengers in cabins-passengers may get infected either by an infectious case in a shared cabin or by pre/asymptomatic crew who continued to work. Estimates of R0 at the beginning of the epidemic were 3.27 (95% CI, 3.02-3.54) and 3.78 (95% CI, 3.49-4.09) respectively for serial intervals of 5 and 6 days; and when quarantine started, with the reported asymptomatic ratio 0.505, R0 rose to 4.18 (95%CI, 3.86-4.52) and 4.73 (95%CI, 4.37-5.12) respectively for passengers who might be exposed to the virus due to pre/asymptomatic crew. Results confirm that the higher the asymptomatic ratio is, the more infectious contacts would happen. We find evidence to support a US CDC report that "a high proportion of asymptomatic infections could partially explain the high attack rate among cruise ship passengers and crew." Our study suggests that if the asymptomatic ratio is high, the conventional quarantine procedure may not be effective to stop the spread of virus.

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Conflict of interest statement

The authors have read the journal’s policy. We wish to confirm that there are no known conflicts of interest associated with this paper and there has been no significant financial support for this work that could have influenced its outcome. AT&T provided the salary for LL but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. Time-dependent effective reproduction number R0 (solid lines) of COVID-19 on board the Diamond Princess ship January 21 (day 1) to February 19 (day 30) and their 95% confidence intervals (dash lines), assuming τ = 5 and 6 days, rp = 0.2 and aratio = 0.505.
Blue: R0 for passengers in contact with asymptomatic crew members. Red: R0 for crew members.
Fig 2
Fig 2. 99 of 100 stochastic simulations of the chain binomial model based on N = 3700 and β = 3.78, assuming no quarantine, serial interval τ = 6 days, infected cases removed, and extrapolation to 90 days, with the observed epidemic (red line).
For the remaining one simulation, the entire population is immune, not infected at all.
See this image and copyright information in PMC

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