It's happened to all of us—you're perfectly healthy when you head off on a trip, and then a few days later, you've got a cough. You can't help but feel it's no coincidence—that a few hours on an airplane consigned you to a week of recovering from a cold. What gives?
There's nothing particularly special about the plane environment. The act of flying doesn't weaken your immune system. The only difference is that you might might be in close contact with more people than you're used to, which makes it more likely that one of them will be sick and pass those microbes on to you. Some studies estimate that up to 20 percent of passengers on commercial airplanes will develop respiratory infections within a week of flying.
One way to get sick is by touching contaminated surfaces, says William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center. There are those people—heck, you might even be one of them—who love to talk about the most germ-covered spots on airplanes. Tray tables, pillows, headrests, armrests, and of course the bathroom; the list goes on and on. Touching a contaminated surface and then putting your hands on your nose or mouth can be a route of transmission, Schaffner says, especially in the summer when intestinal infections are more common.
But for respiratory infections, that's not the "highway" of microbe transmission. For those, it's the air that can get you sick. When a person has a viral infection (99 percent of upper respiratory infections are viral), they generate a cloud of virus in the air around them through coughs or sneezes or simply by exhaling. "If I have a viral infection and I breathe out, my exhalation is full of microscopic viral particles which you can then inhale. They implant on your mucus membranes [like your nose and throat] and you can get the cold," Schaffner says. This viral cloud is within three feet of face-to-face contact, he adds.
On an airplane, you're in close proximity to a lot of people, potentially a lot more than you're used to if you work at a desk job in a cubicle (but maybe not more if you work in retail, for example). But there's also the air. The air on a plane is filtered but it circulates in sections. So even though you're not exposed to the viral clouds of everyone on your flight, you've probably got another two dozen people with whom you are sharing the air. That includes the obvious "coughers and sneezers," Schaffner says, but also people who have a cold but aren't symptomatic yet, as virus particles could be in their breath a day before symptoms set in. So there may be others getting us sick that are less obvious.
The longer you're on an airplane, the longer you're exposed to microbes that might cause disease. "The longer your exposure, the more likely you are to get infected. Even our grandmothers can understand that," Schaffner says. That goes for things like the common cold, but also for more virulent microbes like those that could cause tuberculosis, which are pretty rare. And the more flights you take, the more likely you are to be exposed to microbes from people who might be sick.
There are ways to get more scientific information about the relationship between flying and getting sick, Schaffner says. Researchers could do studies where you sample the air on planes and see how long it takes people to recover from viruses. They could question passengers before and after flying to see how frequently they get sick and when symptoms set in. These studies would be difficult and expensive, he says, and, given that there are many more pressing questions in public health, it shouldn't necessarily be a high priority. "I think we kind of know it [flying] is a risk factor," Schaffner says.
But you don't need fancy studies to tell you what to do to avoid getting sick from flying. Take care of your immune system by drinking water and getting enough sleep. If you're really freaked out, you can wear a face mask to try to filter out some particulates. But for most, the simplest advice is best: "We do know what we can do to avoid getting sick—wash your hands, get your annual flu vaccination, and cross your fingers," Schaffner says.
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