Travel: Planes, Trains, and Germs (cont.)

Even so, there's no definitive proof linking airplane ventilation to disease spread. Overall, the risk of catching something from another infected passenger is about 1 in 1,000 -- about the same as an office building or any other confined space. And Gendreau points out that mathematical models indicate that doubling a plane's ventilation rate would cut the risk of airborne infection by half (using tuberculosis as a model).

Yet airplanes make infection easier in other ways. One example is pressurized air. Planes normally set cabin pressure to what you'd experience at the top of an 8,000-foot mountain. Since cruising altitudes are higher than this, planes cycle air through their engines to pressurize it. That heats the air, which is then cooled. This wrings out just about every drop of moisture.

"We end up with low-humidity, desert-like air," DeHart says. "The longer you fly, the drier your mucous membranes get. And the dryer they get, the more susceptible they are to infection. So in a cabin with nearly 500 people, the air is circulated, the air is filtered -- but still, infectious material gets spread."

Most of that spread comes from the people sitting next to you, and in the two rows in front of you and behind you. If one of these people has a cold, you are at risk.

"The risk is higher than your typical office environment, because of the much higher concentration of people for the air that you have," DeHart says. "The impact of colds is probably more frequent than you would have in just an office setting."

Is There a Health Risk From Pillows, Blankets, and Tray Tables?

Germs don't just fly through the air. They also lurk on contaminated surfaces -- what infectious disease specialists call "fomites."

Gendreau warns that there's a lot of "hype" around this issue. The facts, he says, don't turn up any obvious dangers.

"There have been a number of microbiological content studies of aircraft cabin. In fact, the FAA is currently looking into this," he says. "The British government's aviation health working group recently looked at microbial flora [germs] in two different aircraft types. They found that this stuff is not worse - and maybe better - than other places where people congregate like buildings or other modes of transportation."

DeHart, a frequent flier just back from a trip to Asia, doesn't worry about pillows or blankets, either.

"These blankets and stuff are pretty well cleaned. I don't know in the medical literature of any spread from a fomite like that," he says. "You can't say this hasn't happened. But I don't worry about it. I will certainly use a blanket to stay warm and cozy so I feel like going to sleep. Although usually I use my own air pillow because it adjusts."