Public health crises of the past decade have heightened awareness that new viruses or bacteria could spread quickly across the globe, aided by air travel. While epidemiologists and scientists who study complex network systems are working to create mathematical models that describe the worldwide spread of disease, to date these models have focused on the final stages of epidemics, examining the locations that ultimately develop the highest infection rates. But a new study by Ruben Juanes, Marta González, Christos Nicolaides and Luis Cueto-Felgueroso shifts the focus to the first few days of an epidemic, determining how likely the 40 largest U.S. airports are to influence the spread of a contagious disease originating in their home cities. Read a news story.