Air Traffic Data Reveals Pattern of Influenza A(H1N1) Spread

Researchers at St. Michael's Hospital (Toronto, Canada) and other Canadian institutions analyzed air traffic data on flights leaving Mexico during March and April 2008, and found that a total of 2.35 million passengers flew from Mexico to 1,018 cities in 164 countries. A total of 80.7% of passengers had flight destinations in the United States or Canada; 8.8% in Central America, South America, or the Caribbean Islands; 8.7% in Western Europe; 1% in East Asia; and 0.8% elsewhere. The distribution of flight patterns, gathered from data received from the International Air Transport Association (IATA), was very similar to the ones completed during the same months in 2007. The researchers then compared the international destinations of travelers departing from Mexico with confirmed influenza A(H1N1) infection importations associated with travel to Mexico.

The researchers found that of the 20 countries worldwide with the highest volumes of international passengers arriving from Mexico, 16 had confirmed influenza A(H1N1) importations associated with travel to Mexico (as of May 25, 2009). A receiver-operating-characteristic (ROC) curve plotting the relationship between international air-traffic flows and influenza A(H1N1) importation revealed that countries receiving more than 1,400 passengers from Mexico were at a significantly elevated risk for importation. With the use of this passenger threshold, international air-traffic volume alone was more than 92% sensitive and more than 92% specific in predicting importation. The study was published on June 29, 2009, in a letter to the editor of the New England Journal of Medicine (NEJM).

"Although the correlation between the international movements of travelers and H1N1 is generally intuitive, our findings suggest that quantitative analysis of worldwide air-traffic patterns can help cities and countries around the world better anticipate their risks of importing global infectious diseases,” concluded lead author Kamran Khan, M.D., M.P.H., of St. Michael's Hospital.

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