Intermittent motion behavior at large, crowded events increases risk of disease transmission

What is the typical travel behavior of visitors to large events, such as concerts, and what does this mean for the risk of spreading infectious diseases like COVID-19? A group of researchers from the Institute of Informatics at the University of Amsterdam, together with an epidemiologist from the University of Utrecht, set out to investigate the use of event data in a large stadium from Amsterdam. Their results have just been published in the journal Nature Scientific Reports.

Following the outbreak of the COVID-19 pandemic, governments around the world responded with social distancing measures, including the cancellation of events involving the gathering of large crowds. While it is intuitively clear that crowded events pose a high level of risk for the spread of an infectious disease like COVID-19, much depends specifically on How? ‘Or’ What people move in crowds. Despite a large body of scientific research on crowd dynamics and human mobility over the past decades, surprisingly little is known about human movements in the specific context of large crowded events.

Intermittent model

As the pandemic began, a small group of researchers from the Institute of Informatics were finalizing their analyzes of the movement patterns of visitors to major sports and dance events at the Johan Cruijff stadium in Amsterdam. In two separate publications, they study movement patterns in terms of space and time. The first of these two publications appeared in February 2021 and compared the movements of individuals in crowds to typical foraging patterns that were also present in our human hunter-gatherer ancestors.

More importantly, they found that the individuals were not constantly on the move. People stay in one place for a while and then decide to go somewhere else, usually in an ongoing effort. This leads to an intermittent pattern of movement and rest that is sometimes referred to as “burst” in the scientific literature. This observation only occurs when the movements of people are studied over longer periods, for example several hours.

Infectious risks

The researchers realized that the movement patterns they observed would have important consequences for the spread of a disease like COVID-19. They then collaborated with theoretical epidemiologist Hans Heesterbeek from the University of Utrecht. In the team’s new publication, they reproduce the movement behavior observed in so-called random walk models, on which they simulate the spread of an infectious disease. This second study appeared on September 1 in Nature Scientific Reports.

This new work exposes the perhaps counterintuitive fact that observed intermittent motion behavior exhibits an increased level of risk compared to higher, more continuous motion levels. It would be expected that the more people move around and meet other people, the more individuals become infected. However, if the infection also needs time to spread (rather than happening instantly), people stopping and spending time in close proximity to each other increases the risk of infection.

This shows that, while the probability of infection is time-dependent, an intermittently moving but freely mixing crowd may present the highest level of transmission risk.”

Philip Rutten, PhD Candidate, Study First Author

The researchers point out that this type of crowd movement behavior may be common to various types of events, such as music festivals, religious gatherings, and political demonstrations.

Source:

Journal reference:

Rutten, P. et al. (2022) Modeling the dynamic relationship between the spread of infection and crowd movement patterns observed at large-scale events. Scientific reports. doi.org/10.1038/s41598-022-19081-z.

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