The global spread of emergent infectious diseases can have a dramatic impact on health, society and economics and has become a major challenge for public health. Epidemiological modelling is gaining importance in view of public health decisions, for instance when assessing the consequences of vaccination recommendations.
Dirk Brockmann, Professor at the Humboldt University Berlin (HU) and project group leader at the Robert Koch Institute (RKI), and his colleague Dirk Helbing of ETH Zurich are now presenting a new mathematical theory which improves the understanding of the global spread of epidemics. It has been published in the most recent edition of Science of December 13, 2013 under the title “The Hidden Geometry of Complex, Network-Driven Contagion Phenomena”. With this new approach the place of origin of outbreaks can be determined more precisely and, moreover, it is possible to calculate when an epidemic wave front is expected to arrive at any location worldwide.
Where is the place of origin of a new pathogen? Where will the next outbreaks occur and when? Computer simulations that try to forecast the spread as in modern weather forecasts, are extremely sophisticated and require precise knowledge of disease specific parameters that are, however, typically not known for new, emergent infectious diseases.
Theoretical physicists and complexity researchers Dirk Brockmann and Dirk Helbing have developed a new approach. Their mathematical theory is based on the idea that geographic distances are no longer the key variable but must be replaced with “effective” distances. From the perspective of Frankfurt, for instance, other metropolitan areas such as London or New York are effectively not more distant than geographically close German cities such as Bremen or Leipzig. The researchers have been able to show in their work that the “effective distances” can be computed from the traffic intensities in the worldwide air transportation network: if the flux of passengers from A to B is large, the effective distance is small and vice versa. The researchers then translated this idea into a mathematical theory.
If one visualizes the complex geographic spread of SARS (2003) or Influenza A (H1N1) (“swine flu”, 2009) with this theory, complex spreading patterns turn into regular, concentric wave patterns that can be easily captured mathematically. In this way propagating speeds of diseases can now be computed and one can determine when the effective wave front will arrive at any location on the planet or where an outbreak originated.
RKI and HU have been closely collaborating through a cooperation agreement since 2000. Three of the four departments of RKI deal with the investigation and control of infectious diseases. Dirk Brockmann has a chair at the Department of Biology at HU and leads a project group at RKI. The Robert Koch Institute, the national public health institute for Germany, together with the Humboldt University of Berlin, was able to hire Dirk Brockmann who previously held a position at Northwestern University, Chicago. Among other things, he investigated the spread of infectious diseases based on the movements of banknotes.
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