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COVID-19 outbreak on the Diamond Princess cruise ship: estimating the epidemic potential and effectiveness of public health countermeasures.
J Travel Med. 2020 05 18; 27(3)JT

Abstract

BACKGROUND

Cruise ships carry a large number of people in confined spaces with relative homogeneous mixing. On 3 February, 2020, an outbreak of COVID-19 on cruise ship Diamond Princess was reported with 10 initial cases, following an index case on board around 21-25th January. By 4th February, public health measures such as removal and isolation of ill passengers and quarantine of non-ill passengers were implemented. By 20th February, 619 of 3700 passengers and crew (17%) were tested positive.

METHODS

We estimated the basic reproduction number from the initial period of the outbreak using SEIR models. We calibrated the models with transient functions of countermeasures to incidence data. We additionally estimated a counterfactual scenario in absence of countermeasures, and established a model stratified by crew and guests to study the impact of differential contact rates among the groups. We also compared scenarios of an earlier versus later evacuation of the ship.

RESULTS

The basic reproduction rate was initially 4 times higher on-board compared to the ${R}_0$ in the epicentre in Wuhan, but the countermeasures lowered it substantially. Based on the modeled initial ${R}_0$ of 14.8, we estimated that without any interventions within the time period of 21 January to 19 February, 2920 out of the 3700 (79%) would have been infected. Isolation and quarantine therefore prevented 2307 cases, and lowered the ${R}_0$ to 1.78. We showed that an early evacuation of all passengers on 3 February would have been associated with 76 infected persons in their incubation time.

CONCLUSIONS

The cruise ship conditions clearly amplified an already highly transmissible disease. The public health measures prevented more than 2000 additional cases compared to no interventions. However, evacuating all passengers and crew early on in the outbreak would have prevented many more passengers and crew from infection.

Authors+Show Affiliations

Department of Public Health and Clinical Medicine, Section of Sustainable Health, Umeå University, Umeå, Sweden.Department of Public Health and Clinical Medicine, Section of Sustainable Health, Umeå University, Umeå, Sweden.Department of Epidemiology and Global Health, Umeå University, Umeå, Sweden. Department of Disease Control, London School of Hygiene and Tropical Medicine, UK. Heidelberg Institute of Global Health, University of Heidelberg, Germany.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

32109273

Citation

Rocklöv, J, et al. "COVID-19 Outbreak On the Diamond Princess Cruise Ship: Estimating the Epidemic Potential and Effectiveness of Public Health Countermeasures." Journal of Travel Medicine, vol. 27, no. 3, 2020.
Rocklöv J, Sjödin H, Wilder-Smith A. COVID-19 outbreak on the Diamond Princess cruise ship: estimating the epidemic potential and effectiveness of public health countermeasures. J Travel Med. 2020;27(3).
Rocklöv, J., Sjödin, H., & Wilder-Smith, A. (2020). COVID-19 outbreak on the Diamond Princess cruise ship: estimating the epidemic potential and effectiveness of public health countermeasures. Journal of Travel Medicine, 27(3). https://doi.org/10.1093/jtm/taaa030
Rocklöv J, Sjödin H, Wilder-Smith A. COVID-19 Outbreak On the Diamond Princess Cruise Ship: Estimating the Epidemic Potential and Effectiveness of Public Health Countermeasures. J Travel Med. 2020 05 18;27(3) PubMed PMID: 32109273.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - COVID-19 outbreak on the Diamond Princess cruise ship: estimating the epidemic potential and effectiveness of public health countermeasures. AU - Rocklöv,J, AU - Sjödin,H, AU - Wilder-Smith,A, PY - 2020/02/24/received PY - 2020/02/28/revised PY - 2020/02/28/accepted PY - 2020/2/29/pubmed PY - 2020/5/27/medline PY - 2020/2/29/entrez KW - Basic reproduction number KW - Coronavirus KW - Evacuation KW - Incubation time KW - Isolation and quarantine KW - SARS-CoV-2 JF - Journal of travel medicine JO - J Travel Med VL - 27 IS - 3 N2 - BACKGROUND: Cruise ships carry a large number of people in confined spaces with relative homogeneous mixing. On 3 February, 2020, an outbreak of COVID-19 on cruise ship Diamond Princess was reported with 10 initial cases, following an index case on board around 21-25th January. By 4th February, public health measures such as removal and isolation of ill passengers and quarantine of non-ill passengers were implemented. By 20th February, 619 of 3700 passengers and crew (17%) were tested positive. METHODS: We estimated the basic reproduction number from the initial period of the outbreak using SEIR models. We calibrated the models with transient functions of countermeasures to incidence data. We additionally estimated a counterfactual scenario in absence of countermeasures, and established a model stratified by crew and guests to study the impact of differential contact rates among the groups. We also compared scenarios of an earlier versus later evacuation of the ship. RESULTS: The basic reproduction rate was initially 4 times higher on-board compared to the ${R}_0$ in the epicentre in Wuhan, but the countermeasures lowered it substantially. Based on the modeled initial ${R}_0$ of 14.8, we estimated that without any interventions within the time period of 21 January to 19 February, 2920 out of the 3700 (79%) would have been infected. Isolation and quarantine therefore prevented 2307 cases, and lowered the ${R}_0$ to 1.78. We showed that an early evacuation of all passengers on 3 February would have been associated with 76 infected persons in their incubation time. CONCLUSIONS: The cruise ship conditions clearly amplified an already highly transmissible disease. The public health measures prevented more than 2000 additional cases compared to no interventions. However, evacuating all passengers and crew early on in the outbreak would have prevented many more passengers and crew from infection. SN - 1708-8305 UR - https://www.unboundmedicine.com/medline/citation/32109273/COVID_19_outbreak_on_the_Diamond_Princess_cruise_ship:_estimating_the_epidemic_potential_and_effectiveness_of_public_health_countermeasures_ L2 - https://academic.oup.com/jtm/article-lookup/doi/10.1093/jtm/taaa030 DB - PRIME DP - Unbound Medicine ER -