Mechanistic transmission modeling of COVID-19 on the Diamond Princess cruise ship demonstrates the importance of aerosol transmission
Edited by Andrea Rinaldo, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, and approved January 7, 2021 (received for review July 22, 2020)
Significance
We find that airborne transmission likely accounted for >50% of disease transmission on the Diamond Princess cruise ship, which includes inhalation of aerosols during close contact as well as longer range. These findings underscore the importance of implementing public health measures that target the control of inhalation of aerosols in addition to ongoing measures targeting control of large-droplet and fomite transmission, not only aboard cruise ships but in other indoor environments as well. Guidance from health organizations should include a greater emphasis on controls for reducing spread by airborne transmission. Last, although our work is based on a cruise ship outbreak of COVID-19, the model approach can be applied to other indoor environments and other infectious diseases.
Abstract
Several lines of existing evidence support the possibility of airborne transmission of coronavirus disease 2019 (COVID-19). However, quantitative information on the relative importance of transmission pathways of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains limited. To evaluate the relative importance of multiple transmission routes for SARS-CoV-2, we developed a modeling framework and leveraged detailed information available from the Diamond Princess cruise ship outbreak that occurred in early 2020. We modeled 21,600 scenarios to generate a matrix of solutions across a full range of assumptions for eight unknown or uncertain epidemic and mechanistic transmission factors. A total of 132 model iterations met acceptability criteria (R2 > 0.95 for modeled vs. reported cumulative daily cases and R2 > 0 for daily cases). Analyzing only these successful model iterations quantifies the likely contributions of each defined mode of transmission. Mean estimates of the contributions of short-range, long-range, and fomite transmission modes to infected cases across the entire simulation period were 35%, 35%, and 30%, respectively. Mean estimates of the contributions of larger respiratory droplets and smaller respiratory aerosols were 41% and 59%, respectively. Our results demonstrate that aerosol inhalation was likely the dominant contributor to COVID-19 transmission among the passengers, even considering a conservative assumption of high ventilation rates and no air recirculation conditions for the cruise ship. Moreover, close-range and long-range transmission likely contributed similarly to disease progression aboard the ship, with fomite transmission playing a smaller role. The passenger quarantine also affected the importance of each mode, demonstrating the impacts of the interventions.
Data Availability
Code have been deposited in Zenodo (https://zenodo.org/record/3955528#.XxfUqp5KjIU).
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Cover image: Pictured is the siphonophore Praya dubia deploying its tentacles in the ocean current. Siphonophores are marine animals with elaborate batteries of stinging cells on their tentacles. Through analysis of siphonophores' evolutionary history, Alejandro Damian-Serrano et al. found that predators specializing in one type of prey can become generalists or switch to another prey type. These changes are linked to shifts in the morphology and mode of evolution of the prey-capture apparatus. The findings suggest that predatory specialization may not be an evolutionary dead end. See the article by Damian-Serrano et al., e2005063118. Image credit: Patrick Webster (photographer).
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Copyright © 2021 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY).
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Code have been deposited in Zenodo (https://zenodo.org/record/3955528#.XxfUqp5KjIU).
Submission history
Published online: February 3, 2021
Published in issue: February 23, 2021
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This article is a PNAS Direct Submission.
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The authors declare no competing interest.
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