“Fear of flying” takes on a whole new meaning when you know you could wind up on the same flight as someone infected with a dangerous virus such as Ebola, enterovirus D-68, Middle East respiratory syndrome (MERS) or chikungunya.

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So are commercial airplane cabins really the germ-laden petri dishes we think they are? The answer is yes — and no.

Generally, airplane air is safer than you might think. Most passenger cabins use a 50-50 mix of fresh and re-circulated air. Some 85 percent of large commercial planes clean the re-circulated air with a high-efficiency particulate air (HEPA) filter. A HEPA filter can effectively sift out bacteria and viruses, along with other germs and dust.

“The air quality in an airplane cabin is no riskier than an office building,” says Mark Gendreau, MD, a specialist in aviation medicine at Lahey Medical Center in Peabody, Massachusetts, and author of numerous studies of disease transmission and air travel. “The cabin air only becomes an issue if the disease is fully airborne — and then only if the ventilation system is not working correctly.”

So how did 25 passengers on an Air China flight catch SARS (severe acute respiratory virus) in 2003? SARS is spread by airborne droplets. But some of the sickened passengers were sitting as many as seven rows away from “patient zero” (the traveler who brought SARS on board). Investigators from the Centers for Disease Control and Prevention (CDC) were never able to pin down the chief reason for the contamination because they lacked access to the passengers following the incident. According to Gendreau, some experts speculated the ventilation system was not working properly, while others believed “patient zero” contaminated the bathroom.

There’s no guarantee, even with good ventilation and hand washing (more on this in a minute), that you won’t get sick, especially if you’re sitting close to a sick person for an extended period. But there are ways to lower your risk.

Keep your hands clean

“The main mode for disease transmission when we fly is touching surfaces that are contaminated with microorganism droplets from an infected person, then touching our eyes, nose, and mouth and introduce the disease into our body,” says Gendreau. “The key to staying well while traveling is to sanitize your hands after touching surfaces that harbor infectious germs such as door knobs, and before eating and drinking.”

Be especially careful when touching the restroom door handle and faucet. Studies show they are highly contaminated. The flu, which spreads through airborne droplets, can live on a doorknob for up to 24 hours.

It would be much, much harder to catch Ebola from touching a surface. That virus spreads through direct contact with bodily fluids such as blood or stool. In theory, if a person with Ebola were to bleed or vomit on a surface, and you were to touch that surface and then touch your eyes, nose or mouth, you could get sick. Ebola is not transmitted through the air, and according the CDC, there is no evidence that you can catch it from a cough or sneeze. The virus can live outside the body for up to several hours in dry conditions (say, a smear of blood on clothing) and for 24 hours in wet conditions (a pool of vomit).

After you use the bathroom, scrub your hands with soap and water for a minimum of 30 seconds. Use a paper towel to turn off the sink — and to open and close the door bathroom door. Once you’re back at your seat, give your hands a once-over with alcohol-based hand sanitizer that contains at last 60 percent alcohol. If traveling with children, be vigilant about encouraging or assisting them with proper hand washing.

Keep your hands away from your face

Avoid rubbing your eyes or touching your nose or mouth. When you touch your face, you’re basically giving the germs on your hand a free ride inside. Also, cough and sneeze into your elbow, not your hands.

Give that armrest a wipe down

Germs like to linger in planes. Researchers from Auburn University used germ samples obtained from Delta Airlines and found that methicillin-resistant Staphylococcus aureus (MRSA) could survive for five days on plastic and seven days on cloth when subjected to the temperature and humidity typical of an airplane cabin; E. coli lived three to four days. The scientists also discovered that plane surfaces have high "transmissibility," meaning that the long-lived bacteria moved easily from the plastic and cloth to human skin.

Immediately after sitting down, wipe your armrest, seat pocket and tray table with an antibacterial wipe. Store the dirty wipes in a sealable plastic sandwich bag (bring a stash with you).

Bring a mask onboard if it makes you feel better

Many studies don't support the effectiveness of wearing a surgical mask over your nose and mouth unless you're the one who's sick, says Gendreau. (If you’re the sick person, the mask could help prevent the spread of your germs to others.) But some experts say masks can be protective against certain germs such as swine flu because the virus particles are larger and therefore easier to trap. Keeping a mask in your carry-on gives you the option of slipping it on if you find yourself next to a passenger who's clearly sick.

Related: Germ-Proof Your Commute

Better still, ask to be moved away from your sick seatmate. The CDC recommends, when possible, the airline move the sick passenger at least 6 feet away from any other passengers.

Spritz your nose

A must-have on any flight is saline nasal spray. These sprays not only moisten your nasal passages, they also help your body flush out germs. According to Gendreau, saline solution boosts the effectiveness of the tiny hair-like cilia that line your nasal passages, which move back and forth to waft germs away. Saline drops for your eyes are a good idea, too, especially for contact lens wearers. If your contacts are really drying out your eyes, it’s best to remove them (with clean hands!) so you’re not tempted to rub your eyes.

Drink up

Commercial jets fly above 30,000 feet, where the humidity is well below the 15 percent needed to keep your skin and mucous membranes healthy. Once that air is filtered and re-circulated, it's even drier, making it even more important to drink water both before and during your flight. Hot drinks are also helpful because the steam moistens mucous membranes. 

Related: Is it Safe to Drink the Water on a Plane?