Air travel doesn't pose extra risks for individuals, infectious disease experts say, but it does spread diseases between populations.

Passengers may worry viruses will spread around planes in recirculated air, but that isn't a concern thanks to the high efficiency particulate filters that catch microbes, said Dr. Anthony Evans, chief of aviation medicine for the Montreal-based International Civil Aviation Organization.

"Any air that's been recycled through so called HEPA filter will be clear to all intents and purposes of any harmful viruses or bacteria," Evans said.

The real risk, whether on a plane or at a theatre, comes from being in close contact with someone who is infected, he said.

Jets transport two billion passengers every year, and can take a disease anywhere on Earth within 48 hours. In the early stages of outbreaks of both SARS and the H1N1 pandemic, people who weren't showing symptoms carried the viruses to unsuspecting countries.

Canadian researchers have used computer modeling and international aviation data to predict infectious disease outbreaks by tracking patterns of travel between countries.

It's too late to use travel restrictions on airline passengers to stop the spread of the H1N1 virus, but the findings could help health agencies to get a jump on the next viral threat, said study co-author Dr. Michael Gardam, director of infection prevention and control at Toronto's University Health Network.

"We're able to look at the air transportation network and … predict very accurately, no matter where a disease shows up in the world, we can say where it's going to go," said Gardam.

The Public Health Agency of Canada and the World Health Organization are studying the research.