The movement of people around the globe, depicted here in a map of air traffic among the 500 largest international airports, can lead to the rapid spread of infectious disease.

The movement of people around the globe, depicted here in a map of air traffic among the 500 largest international airports, can lead to the rapid spread of infectious disease.

In this rapidly shifting and interconnected world, infectious agents continually find new niches. The 2009 “swine flu” pandemic starkly illustrated the impact of globalization and air travel on the movement of infectious diseases—with the infection spreading to 30 countries within 6 weeks and to more than 190 countries and territories within months.


The human population is undergoing a mass migration from the countryside to “megacities.” Throughout history, big cities have been great incubators of infections—with outbreaks of respiratory, gastrointestinal, meningeal, and skin infections becoming common in crowded urban settings. Substandard housing and inadequate sewage and water management systems incubate disease vectors such as mosquitoes and rats. Poor access to health care services worsens the spread of infection.


Globalization of the food supply has spread disease caused by bacteria such as Salmonella and E. coli O157:H7. The United States, for example, imports about 20 percent of its fresh vegetables, 50 percent of its fresh fruits, and more than 80 percent of its fish and seafood. As wealthy nations demand such foods year-round, the increasing reliance on producers abroad means that food may be contaminated during harvesting, storage, processing, and transport—long before it reaches overseas markets.


Food is not the only globally traded product to set off waves of infection. In 1999 the fungus Cryptococcus gattii emerged on Vancouver

Sao Paulo, Brazila modern megacity.

Sao Paulo, Brazil—a modern megacity.



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