Abstract
Population migration plays a critical role in the spread of disease by initiating outbreaks of acute diseases, changing the prevalence of infectious diseases at a given location, and changing the face of chronic disease resulting from previous infection. This article focuses on the recent demographic changes in North America that have facilitated the introduction and spread of new microbial threats, the role migrant populations play in changing the demographics of specific infectious diseases, and the potential responses of clinicians and public health officials in addressing the challenges posed by these infections. The emphasis of the article is on immigrant and migrant populations entering North America; the role of travelers in emerging infectious diseases is addressed in another article in this issue.