Only a flight away? Swine flu followed route map

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - Health experts are fond of saying any new disease is just a flight away from anywhere, and a report published on Monday shows the new strain of H1N1 flu followed the airline route map as it spread around the globe.

The swine flu virus spread first and quickest in March and April in the United States and Canada -- where 80 percent of airline passengers traveled in March and April of 2008, researchers at St. Michael's Hospital in Toronto found.

Dr. Kamram Khan of St. Michael's and colleagues used International Air Transport Association data for their study. They said travel patterns were also similar in 2007 and therefore likely to be similar in 2009.

"This work provides the world with a potent early warning system for emerging infectious diseases," Dr. Michael Gardam of the Ontario Agency for Health Protection and Promotion said in a statement.

"Our analysis showed that in March and April 2008, a total of 2.35 million passengers flew from Mexico to 1,018 cities in 164 countries," Khan and colleagues wrote in the New England Journal of Medicine and published at h1n1.nejm.org/.

Los Angeles had the most travelers, with 221,494 passengers arriving from Mexico in March and April of 2008. New York followed with 126,345. The first non-U.S. city was Toronto, No. 12, with 44,854 passengers arriving from Mexico.

The World Health Organization has confirmed 70,893 cases of the new H1N1 swine flu pandemic, with 311 deaths. However, U.S. health officials last week said there were likely at least 1 million cases there alone. Iraq, Lithuania, Monaco and Nepal all confirmed their first cases on Monday.

The first cases were detected in two California children in April, but tests showed the first known infections were in Mexico. By the time they had identified a new virus, U.S. officials said it had spread too far and too fast to try to stop it.