New research at UCSB is making strides at tracking potential epidemics by following the money.
UCSB Kavli Institute for Theoretical Physics post-doctorate fellow Lars Hufnagel, along with fellow researchers, recently completed a project analyzing how diseases spread by using www.wheresgeorge.com, a website that allows anyone to track any denomination of U.S. paper currency by inputting the serial number. Using the data from the website, the researchers were able to create new models for how people – and epidemics – travel around the world based on the movement of currency. Hufnagel worked with Dirk Brockmann, a post-doctorate fellow at the German-based Max Planck Institute (MPI) for Dynamics and Self-Organization, and MPI Director Theo Geisel on the project.
The outbreak of Severe Acute Respiratory Syndrome (SARS) prompted the group to conduct their initial research in 2003, Hufnagel said. They submitted a proposal entitled “Pandemic Diseases and the Aviation Network: A Case Study,” to the American Physical Society in December 2004.
Figuring out how humans move on a large scale was the first step of the process, Hufnagel said. He said the researchers originally focused on the movement of individual travelers, using airline records to develop their models.
“We were basically using the worldwide aviation network [that follows where people fly] to see if one can know how disease spreads from one country to the other,” Hufnagel said. “It was not sufficient to use just the aviation network [because it doesn’t take into consideration trains and cars].”
Looking at the movement of money, Hufnagel said, gave scientists a better concept of how people move and interact, allowing the researchers to match up the results with current knowledge about the spread of disease and see what patterns would be likely in the case of a widespread epidemic.
“Local infection happens during contact, which is specific,” Hufnagel said. “Spatially, we needed to incorporate large movement. We wanted to quantify how people move around in the United States and marry this part of the study [with] how an epidemic will spread now, compared to in the past, and see how the model is.”
Hufnagel said that the group’s studies revealed that disease spreads based on a predictable phenomenon.
“What was really surprising was that this movement can be described in such simple mathematical terms,” Hufnagel said. “What was further surprising was that this is independent of where you live in the United States – whether you live in a big city or a small city. Disease spreads through one-on-one contact, but it’s also important to look at large spread, such as mass movement.”
Hufnagel said epidemics spread differently than in the past because people move across large distances more rapidly since the advent of cars, trains and airplanes, although short-distance travel is still much more commonplace.
“It’s clear that people move short [distances] way more often than long distances, [like when] going to work,” Hufnagel said. “These are many small movements, and once in a while [people] fly across the nation.”
Hufnagel said past epidemics took a long time to spread, such as the fourteenth-century Black Plague that took several years to spread from southern to northern Europe. Now, however, because people move more quickly, there is a higher likelihood of coming into contact with an infection. The spread of SARS and avian influenza are some cases of rapidly moving diseases.
“You can use any [disease to track its spread],” Hufnagel said. “Then one can come up with predictions and then hopefully see how one can contain an epidemic. The immediate next step that we’re working on right now is to combine [what they know about human movement and disease] and see how well it works.”