Cities receiving the most arrivals from Mexico were Los Angeles, New York, Chicago, Miami, Houston and Minneapolis-St. Paul.
Of the top-20 destination countries, only one -- Venezuela -- had no confirmed cases of swine flu as of May 25, 2009. Japan, Chile and Peru had confirmed swine flu cases, but there was no known association with travel to Mexico, according to the correspondence.
All of the others had confirmed cases of swine flu related to travel from Mexico as of May 25.
"The traffic was so strongly correlated with the importation of this disease," Khan said. "Where people go, infectious diseases of people will follow."
Conversely, the nations that were not among the top-20 destinations for passengers from Mexico had few or no cases of travel-associated swine flu.
"Almost all the imported cases were in the countries with high-traffic volumes of passengers from Mexico," Khan said. "Almost no importations were in the countries with low-traffic volumes."
On June 11, the World Health Organization declared swine flu a pandemic as infections climbed across North America, Australia, South America, Europe and elsewhere. An estimated one million Americans have been infected with the H1N1 swine flu, though in most people symptoms are mild, according to U.S. health officials.
The database used in the study, called the Bio.Diaspora Project, includes world air-travel patterns that represent 99 percent of the world's commercial air traffic, Khan said. The information, which was collected with the cooperation of several international airport and airline associations, includes itineraries from 2.2 billion passengers and flight schedules from 3,500 airports in
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