Mechanistic transmission modeling of COVID-19 on the Diamond Princess cruise ship demonstrates the importance of aerosol transmission

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.

Association of social distancing and face mask use with risk of COVID-19

“…Since the app did not collect the data regarding the other behaviors, we were not able to adjust for them. However, there is growing evidence that COVID-19 may spread through aerosols [42][43][44] . Since hand washing does not effectively prevent aerosol transmission while the face mask use does 45 , it is less likely that our findings were confounded by hand washing.…”

Modes of transmission of SARS-CoV-2 and evidence for preventive behavioral interventions

“…After investigating the potential contributions of respiratory droplets, aerosols, and fomites among new cases of COVID-19 aboard the Diamond Princess cruise ship, Azimi et al concluded that short-range aerosols were the dominant mode of transmission [15] . Investigating the same outbreak, Xu et al did not find a substantial increase in cases after the stay-in-room policy was implemented, leading them to conclude that the virus was not spread through the central air-conditioning to individual rooms, and that long-range aerosol transmission may not be possible [16].…”

Action Levels for SARS‐CoV‐2 in Air: Preliminary Approach

“…The importance of both shorter range and longer range routes of exposure for community transmission has been borne out in studies of outbreaks, in particular the Diamond Princess cruise ship (Azimi et al., 2020) and the Skagit WA choir cluster (Miller et al., 2020). Modeling studies also indicate that both routes are important in the health care setting (Jones, 2020).…”