What is the typical movement 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 study the question using data from events held in a large stadium. from Amsterdam. Their findings were 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 canceling events involving the gathering of large crowds. While it is intuitively clear that events involving crowds pose a high level of risk for the spread of an infectious disease like COVID-19, a lot depends on how the events are organised. comment people move in crowds. Despite a great deal of scientific research on crowd dynamics and human mobility over the past few decades, surprisingly little is known about human movement in the specific context of large-scale, high-traffic 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 sporting and dancing 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, published in February 2021, compares the movements of individuals in crowds to typical foraging patterns that were also present in our 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 results in an intermittent pattern of movement and rest, sometimes referred to as a “burst” in the scientific literature. This observation only appears when the movements of people are studied over longer periods of time, for example several hours.
Risks of infection
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 the theoretical epidemiologist Hans Heesterbeek of 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 was published on September 1 in the journal Nature Scientific reports.
This new work exposes the fact, perhaps counterintuitive, that observed intermittent movement behavior has an increased level of risk compared to higher and more continuous levels of movement. One would expect that the more people move around and meet other people, the more infected they become. However, if the infection also needs time to be transmitted (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, a crowd moving intermittently but freely mixing 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.
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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.