Disease Travel

To understand how epidemics spread epidemiologists need information about both the local infection dynamics — how the disease is transmitted from one person to another, which is a very disease-specific factor — and how people move around in the country.

Hufnagel and his colleagues first started studying the spread of disease in order to try to understand how the SARS epidemic spread in 2000. "The worldwide aviation network is sufficient to explain how SARS spread around the world," he explains. "But it was also clear that if you want to model how epidemics spread on a smaller scale, that you need to incorporate other means of transport, like people driving by car or by bus and train."

Diseases, like money, are transported from place to place by people.

"So we analyzed roughly half a million dollar bills how they move around the United States," he says. The bills' movements were followed for about a week.

The global spread of infectious disease. image: Lars Hufnagel, UCSB

He says that his model may not apply to all infectious diseases, but hopes it will help public health officials come up with measures to stop the spread of an epidemic in the United States and around the globe.

The U.S. government is currently gearing up for the arrival of bird flu as concerns grow that it could soon show up on U.S. shores with migrating birds. The proposed response plan for a bird flu outbreak in people assumes a worst-case scenario where as many as 90 million people in the U.S. would become sick.

Hufnagel's research was published in the January 26, 2006 issue of Nature, and was funded by the Max Planck Society (Germany), and the National Science Foundation.