Gendreau studies germiness while traveling, and he knows just how infectious travel can be.
"The risk of contracting a contagious illness is heightened when we travel within any enclosed space, especially during the winter months, when most of the respiratory viruses thrive," Gendreau said.
Studies show that germs can travel easily on an airplane, where people are packed together like sardines.
For example, a woman on a 1994 flight from Chicago to Honolulu transmitted drug-resistant tuberculosis to at least six of her fellow passengers, according to a New England Journal of Medicine study.
In 2003, 22 people came down with severe acute respiratory syndrome from a single fellow passenger who had SARS but didn't have any symptoms, according to another New England journal study.
But the airplane isn't the only place along your travel route where germs thrive. Here are five ways to avoid germs while traveling.
1. Sit toward the front of the airplane.
"Pick a seat near the front, since ventilation systems on most commercial aircraft provide better air flow in the front of the aircraft," Gendreau advised. If you can afford it, sit in first class, where people aren't so squished together.
2. Don't drink coffee or tea on an airplane.
Monitoring by the Environmental Protection Agency shows that water in airplanes' water tanks isn't always clean -- and coffee and tea are usually made from that water, not from bottled water, according to Victoria Day, a spokeswoman for the Air Transport Association.
The EPA advises anyone with a suppressed immune system or anyone who's "concerned" about bacteria to refrain from drinking coffee or tea on an airplane.
"While boiling water for one minute will remove pathogens from drinking water, the water used to prepare coffee and tea aboard a plane is not generally brought to a sufficiently high temperature to guarantee that pathogens are killed," according to the EPA's website.
According to the EPA, out of 7,812 water samples taken from 2,316 aircraft, 2.8% were positive for coliform bacteria. Although that sounds like a small number, this means 222 samples contained coliform bacteria.
3. Sanitize your hands after leaving an airplane bathroom.
A toilet on an airplane "is among the germiest that you will encounter almost anywhere," said Charles Gerba, an environmental microbiologist at the University of Arizona who's also known as "Dr. Germ."
"You have 50 people per toilet, unless you are flying a discount airline; then it is 75," Gerba said. "We always find E. coli on surfaces in airplane restrooms."
You should wash your hands after using the restroom, but because the water itself might have harmful bacteria (see No. 2 above) and because the door handle on your way out has been touched by all those who went before you, Gendreau also advises sanitizing your hands when you return to your seat.
4. Wash or sanitize your hands after getting off an escalator.
Gendreau says tests show that escalators in airports are full of germs.
To confirm these tests, here's a fun activity while you wait for your flight this Thanksgiving: Look at your watch, and count how many people get an escalator in a five-minute time period. Multiply that by 12, and you have how many people are on that escalator every hour.
High-volume handrails are why Gendreau sanitizes his hands as soon as he can after he exits an escalator.
5. Wash or sanitize your hands after using an ATM.
Gendreau says ATMs, especially in busy places like airports, are full of germs. As with escalators, he sanitizes ASAP after using one.
Gendreau says that keeping healthy while traveling can be summed up in six words: "hand hygiene, hand hygiene, hand hygiene."
Keeping your hands clean is crucial, he says, when you're spending the day touching surfaces that have been touched by hundreds or thousands of people before you.