Modern jet travel now allows passengers to move from virtually any place in the world to any other place within 36 hours-less than the incubation period of many viral and bacterial diseases. This means that infections can become globally disseminated before clinical disease is recognized. The SARS outbreak of 2003, which quickly spread to 29 countries, and the ongoing, novel H1N1 infl uenza pandemic (see Pappaioanou and Gramer 2010 in this issue) dramatically underscore thi point. As such, the notion of “foreign” or “exotic” diseases has become less meaningful. A wide range of diseases now have the potential to crop up unexpectedly anywhere in the world and some may quickly become endemic; for example, West Nile virus infection was unknown in North America before 1999 but is now fi rmly established on much of the continent.