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."

If you're going to worry about contamination on airplanes, shift your focus from the overhead compartment to the onboard water system. A recent EPA study found coliform bacteria - germs associated with feces - in water from galley water taps and lavatory faucets in 17% of airplanes tested.

Every expert tells WebMD the same thing: The best way to protect yourself against germs is to wash your hands. Hand washing removes viruses as well as bacteria. Of course, it gets complicated if the water you wash with is itself contaminated.

Gendreau has a solution. He carries a portable bottle of alcohol-based hand-sterilizing gel. The gel isn't as good at killing viruses as soap and water. So Gendreau washes his hands - then uses the gel.

"What I typically do is wash my hands a lot. If you're going to get something through a seat table, pillow, or what not, washing your hands is the way to minimize your risk," he says. "You wash in that washroom, but what is the coliform content on your hands now? So that is why I slap on the alcohol gel. Within 10 seconds it kills all the bacteria."

DeHart has more tips.

"Be healthy and rested before making a flight," he says. "If you already are coughing and under the weather, you will be worse after flying. So you need to have taken good care of yourself, and ensure you are taking the medications you should be taking. If you have any question of health -- your heart, particularly -- check with your doctor before flying. And as you're flying, you need to hydrate as much as you can. The flight crews are good at distributing water. You should drink that, and take a bottle or two yourself on board. Hydration is a must."

Off on a Cruise, the Germs Don't Snooze

If airplane ventilation has you worried, maybe you're thinking of taking an ocean liner instead. After all, there's a lot of fresh air out on the open seas, isn't there?

Of course there is. That may be one reason why 9.4 million people last year sailed out of U.S. ports.

With a change in transportation mode come changes in disease risk, DeHart says.

"Cruise ships provide an entirely different environment. You are there for days, dependent on them for all your meals, and on the ship crew for hygiene," he says. "You are thrown in with many more people than on an airplane, so there is a much greater chance of communicable disease being present. ... And some viruses just go ape when they get on a cruise ship with a lot of people."

Such viruses tend to be the notorious noroviruses. Noroviruses cause what many people call "stomach flu" -- although these bugs have nothing at all to do with the flu. What they do is cause nausea, vomiting, and stomach cramps. And they spread like wildfire. All it takes is for you to touch a contaminated surface and then touch your mouth.

Because of the recent rash of norovirus outbreaks on cruise ships, the CDC keeps a close watch. Lisa Beaumier is a public health analyst with the CDC's vessel sanitation program. Beaumier says noroviruses are likely everywhere, not just on cruise ships.