A team of Canadian researchers analyzed the air traffic patterns during March and April of this year, looking for correlation between departure/arrival cities of passengers and the spread of H1N1 swine-origin influenza. Turns out that the two are closely correlated and confirm that airports are gateways of pathogens as well as vacationing tourists.
Our analysis showed that in March and April 2008, a total of 2.35 million passengers flew from Mexico to 1018 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; 1.0% in East Asia; and 0.8% elsewhere. These flight patterns were very similar to those during the same months in 2007 (see Fig. 1 in the Supplementary Appendix). We then compared the international destinations of travelers departing from Mexico with confirmed H1N1 importations associated with travel to Mexico, and we found a remarkably strong degree of correlation. Of the 20 countries worldwide with the highest volumes of international passengers arriving from Mexico, 16 had confirmed 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 H1N1 importation revealed that countries receiving more than 1400 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, with an area under the ROC curve of 0.97.
Letter to NEJM: Spread of a Novel Influenza A (H1N1) Virus via Global Airline Transportation
