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Fresh or Recycled Air? Colds Don't Care


Air travelers who worry about picking up germs from recycled cabin air can breathe a little easier: Passengers inhaling recirculated air don't come down with more colds than travelers on planes ventilated with fresh air, a new study says.

Researchers at UC San Francisco interviewed more than 1,100 people who had flown from the San Francisco Bay Area to Denver in 1999. About 19% of travelers on planes with recirculated air reported getting colds after their flight, while a comparable number--21%--of passengers on aircraft with fresh air got colds, according to the study, which was published in the July 24 issue of the Journal of the American Medical Assn.

The study was launched in response to a widespread perception that flying increases risks of getting a cold, researchers said. Outbreaks of influenza and tuberculosis aboard aircraft have been documented, and--in other settings at least--sitting in confined spaces with limited ventilation for prolonged periods increases one's risk of catching a cold. Further, recirculated air had been shown to boost rates of cold virus transmission in Army barracks.

"This had never been studied in airplanes, " said Dr. Jessica Nutik Zitter, a study coauthor. "There are many routes of transmission for the cold virus, but recirculated air isn't one of them."

The study should be welcome news for passengers--most of the planes ventilated with fresh air have been retired since the study was conducted. In older aircraft, fresh air was pumped into the cabins after it had been compressed, humidified and cooled by the engines, but the process burned up a lot of fuel. To boost energy efficiency, aircraft makers started using ventilation systems that recirculated cabin air in the early 1980s.

Newer aircraft recirculate as much as 50% of cabin air, which passes through heavy-duty filters that pick up infectious bugs before the air is pumped back into the passenger compartment. (A filter's ability to capture tiny viruses, however, is limited.)

With the post-Sept. 11 airport security restrictions, a study of this nature could probably never be done again. "We were beating the runways looking for volunteers," says Zitter.

Researchers buttonholed travelers waiting at the gates for their flights, eliminating people who had colds already, had flown during the previous week, or had plans for additional air travel before the follow-up interview.

They distributed preflight questionnaires to volunteers who met their criteria, and even boarded planes awaiting takeoff to retrieve the surveys.

"We were running up and down the aisles grabbing questionnaires from people right before the planes took off," says Zitter. Passengers were then contacted about a week later to determine whether they had contracted a cold.

Still, "these results don't address the increased risk of getting sick if you fly," says Zitter. Cold viruses can also be transmitted from physical contact with someone who is infected. And there's plenty of opportunity to spread germs when you're sitting in close quarters with 100 or so strangers on an aircraft--by touching bathroom door handles, upright trays, armrests, even pillows and blankets that have been used by people who are sick.

You just can't blame the cabin air anymore for your cold.

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