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The Globe and Mail

Air travel patterns may predict virus spread

Canadian researchers have designed a system based on air travel patterns to predict how infectious diseases will spread around the world, offering a means of halting transmission by taking preventive measures as soon as an outbreak occurs.

The system, developed by infectious-disease physician Dr. Kamran Khan and colleagues, accurately predicted how the H1N1 flu virus would circulate worldwide after arising in Mexico earlier this year.

Using their BIO.DIASPORA system, the team analyzed the flight itineraries of more than 2.3 million passengers who departed Mexico on commercial flights during March and April 2008 to predict the spread of H1N1 a year later.

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The findings show the international destinations of air travellers leaving Mexico -- including cities in Canada -- were strongly associated with confirmed importations of the virus around the world.

"We know that infectious diseases don't respect national boundaries, but if there is one thing they have to respect as they're spreading around the globe, it's the architecture of the airline transportation system," said Khan of St. Michael's Hospital in Toronto.

"This is their mechanism for spreading around the globe."

Khan said he came up with the idea of using the air traffic grid to better understand the global transmission of infectious disease after the 2003 SARS crisis. That outbreak killed more than 770 people, including 44 Canadians.

"It just became so obvious how the airline transportation network was a major conduit of the spread of infectious diseases," he said.

In what Khan calls a case of "bizarre timing," days before he and his team were to deliver a report on BIO.DIASPORA to the Public Health Agency of Canada (PHAC), news began trickling out about a new flu virus in Mexico. Their system allowed them to track its spread as it quickly infiltrated populations in one country after another.

"The movement of passengers out of Mexico aligned very nicely with the observed spread of H1N1," said Khan, principal author of a paper on the initiative published this week in the New England Journal of Medicine.

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"I see this publication as being an important point now where we can say: Okay, this is proof of principle that where people move, infectious disease of people will follow, that that principle now is validated in this H1N1 outbreak."

Co-author Dr. Michael Gardam, director of infectious diseases prevention and control for the Ontario Agency for Health Protection and Promotion, said the system provides for the first time an accurate picture of not only where diseases will travel, but how often and when.

"This work provides the world with a potent early-warning system for emerging infectious diseases," he said.

The obvious next step is to use the system for prevention, said Khan, adding that Canada is particularly vulnerable to infectious disease threats via air travel and because of our proximity to the United States.

"Collectively, when we look at Canada and the United States, we generate and receive about one-sixth of the entire world's international air traffic. That's a lot for two countries."

In their 122-page report to PHAC, the researchers found:

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13 countries produce 80 per cent of all air traffic into Canada, primarily to airports in Toronto, Vancouver and Montreal -- in that order. These cities receive more than 13 million international passengers every year.

60 per cent of all passengers travelling to Canada from developing countries arrive after multiple flights. About half -- or 1.4 million a year -- make airplane connections through just nine cities: London, Hong Kong, Tokyo, Frankfurt, Paris, Miami, Amsterdam, New York and Chicago.

Four developing countries -- China, Mexico, India and the Philippines -- and nine industrialized countries -- the United States, Britain, France, Germany, Italy, the Netherlands, Japan, South Korea and Taiwan -- are the source of 80 per cent of Canada's international air traffic.

These countries are key locations from which future infectious disease threats may originate or pass through en route to Canada, Khan said, noting that it would be ideal to diagnose infected passengers before they board airplanes from locales where an epidemic has taken hold.

"We don't want to be having to deal with threats after they arrive at our border," he said. "It would be nice if we could get ahead of the curve and start thinking about preventing them and mitigating their risk before they arrive.

"That's really the preferred approach. Ideally if you can contain an outbreak before it even reaches an airport, that benefits the entire global community."

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