Christos Nicolaides, Juanes Research Group, MIT
A contagion map shows flights in and out of the top 40 airports.

Air travel — and airport design — may be key to the spread of a contagious disease, as well as efforts to put a lid on it, according to research from the Massachusetts Institute of Technology. Using network theory, the MIT researchers examined how air travel could play a role in spreading a pandemic virus and how containment efforts at airports could help curb a global spread.

From the 2003 outbreak of SARS, which killed 1,000 in 37 countries to the 2009 H1N1 flu pandemic that killed 300,000 globally, air travel has played a part in the spread of viral or bacterial infections, the researchers said in the study, published in the journal PLoS ONE.

The study ranks New York's John F. Kennedy International Airport and the Los Angeles International Airport as top global "super-spreaders" of a deadly virus. Next would be Honolulu International Airport. It's not simply a matter of which airport has the most travel. In the case of Honolulu, its location and links to major international hubs would make those passing through it more vulnerable than they would be in some higher-traffic airports. Even wait times for flights impact the disease-spread potential.

"Study authors said the effort moves contagion research forward by highlighting where U.S. health officials could focus attention immediately following an outbreak," wrote Elise Viebeck of Healthwatch, a blog on thehill.com.

Using network theory to create a new model, the researchers ranked the 40 largest U.S. airports in terms of how they would influence the spread of a contagious illness that started in their home cities. According to a release accompanying the study, "this new approach could help determine appropriate measures for containing infection in specific geographic areas and aid public health officials in making decisions about the distribution of vaccinations or treatments in the earliest days of contagion."

While mathematical models have been created to look at how disease spreads, the background information for the study said most look at the final stages of epidemics and which areas developed the highest infection rates.

"Our work is the first to look at the spatial spreading of contagion processes at early times and to propose a predictor of which 'nodes' — in this case, airports — will lead to more aggressive spatial spreading," said Ruben Juanes, an associate professor in MIT's Department of Civil and Environmental Engineering, in a written statement. "The findings could form the basis of an initial evaluation of vaccine allocation strategies in the event of an outbreak and could inform national security agencies of the most vulnerable pathways for biological attacks in a densely connected world."

The research combines two different types of movement studies. Juanes applied his research of the flow of fluids through fracture networks in subsurface rock, while his colleague Marta Gonzalez used cellphone data to show human mobility patterns and trace contagion processes in social networks. The combination created a foundation for looking at individual travel patterns among airports. Existing models have been based on a theory of "random homogeneous diffusion of travelers" from airport to airport.

The problem with those methods, according to the researchers, is that people don't travel randomly, but instead create patterns that can be duplicated for the purpose of modeling. Using Gonzalez's work on human mobility patterns, Juanes and his team applied Monte Carlo simulations to determine the likelihood of a single traveler flying from one airport to another.

If it were just a matter of traveler volume, it would seem that half the travelers at the Honolulu airport would go to San Francisco and the other half to Anchorage, spreading the disease in those locations, where it would then be passed on to other destinations. But the new model found that while the Honolulu airport gets only 30 percent as much travel as Kennedy International Airport, it has nearly as much impact on contagion because of "its location in the Pacific Ocean and its many connections to distant, large and well-connected hubs." It ranks third in contagion-spreading influence, the researchers said.

No. 1 is Kennedy, followed by airports in Los Angeles, Honolulu, San Francisco, Newark, Chicago (O'Hare) and Washington (Dulles). Atlanta's Hartsfield-Jackson International Airport, which has the most flights pass through, ranks only No. 8 in contagion influence. Boston's busy Logan International ranks 15th.

A video showing the potential patterns of spread is available on nature.com.

The study was supported by a Vergottis Graduate Fellowship and awards from the NEC Corporation Fund, the Solomon Buchsbaum Research Fund and the U.S. Department of Energy.

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