Sneezing and droplet exposure.

My wife and I had just settled into our seats for a flight from Burlington. She had the window and I the aisle. The parade of embarking passengers stalled due the usual boarding confusion in the rear of the aircraft. A small child was standing with his mother in the aisle next to my seat. He was coughing loudly. Suddenly, while staring directly at me, he sneezed. His mother instantly reminded him to cover his mouth when he sneezed.

My public health brain immediately roared into action. I recalled the story of the Emirates Airlines plane from Dubai that landed at Kennedy Airport last September only to have 10 passengers admitted to the hospital with flu-like illnesses while an additional 106 reported a range of gastrointestinal and upper respiratory symptoms. Was this to be our fate? Or something worse?

Is there something about air travel that makes it more likely we will get sick than travel by train, bus or boat? Let’s look at some data.

Worldwide roughly 3 billion people fly each year. This translates to more than 8 million people each day. Suppose that on any given day just 1 percent (80,000 people) have a cold, flu, a diarrheal illness or perhaps a more serious communicable disease. This means that a portion of these 80,000 travelers are passing through airport terminals, are in security lines and, of course, will be locked into an aircraft with us for anywhere from one to 14 hours. If this sounds like a recipe for trouble, you are correct. In fact, it is exactly the scenario that public health experts around the world fear most as they contemplate the potential for the spread of avian flu, Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).

Interestingly—and surprisingly, there is very little published data on respiratory illness transmission among airline passengers. Only about a dozen documented cases of inflight infectious disease transmission have been reported in the literature. However, what data exist show the risks of transmission on an aircraft are quite low. A March 2018 study from Emory University and Georgia Tech reported on behaviors of 1,540 passengers on 10 different transcontinental flights. Only one passenger was observed coughing. In addition, 229 air and surface samples (trays, seat belt buckles, lavatory handles) tested negative for 18 common respiratory viruses.

How is it that these data seem so at odds with so much of what we read and hear anecdotally about flying?

The problem with this and similar studies is that flying involves more than the inflight portion of the experience. Check-in, passing through security, eating, using the restrooms, frequenting waiting areas prior to boarding are all opportunities for disease exposure.

If one thinks about the complexities of conducting such studies, the dearth of consistent data is not so surprising. For one thing, passengers who become infected on a flight likely don’t develop symptoms until days later. Similarly, people may already be ill, have not developed symptoms, yet are still infectious. It’s only when a large and sudden outbreak occurs either during or immediately after a flight, such as with the Emirates flight last September, that investigators can go to work. There is also solid research that shows that the total air travel experience offers an efficient transmission pathway for various respiratory and nonrespiratory diseases.

For example, three recent surveys conducted for the Canadian Broadcasting Company, National Broadcasting Company and Insurance Quotes used certified microbiologists to obtain samples from TSA bins, arm rests, tray tables, restroom buttons and latches, and seat pockets from U.S. and Canadian aircraft. Staph, E. coli, pseudomonas and other disease-causing pathogens (“bugs”) were identified, some at extremely high concentrations. (See below for links to reports.)

Since refusing to fly hardly seems like a viable option, what can we do to avoid encountering these pathogens while flying?

The principal pathways for disease transmission for the air traveler include indirect transmission—such as touching a contaminated surface such as a seat belt buckle or tray table and then touching your hands, mouth or eyes—and droplet or air transmission, such as when someone sneezes nearby or we inhale tiny microscopic particles circulating in the air.

There is some good news for those wishing to avoid air or droplet transmission of infectious disease. The first is that research shows that, unless one is within 3 or 4 feet (one or two rows on a plane) of someone who is ill, the likelihood of droplet transmission is low. Second, and contrary to general belief, filtration and decontamination of air recirculated on modern aircraft is highly effective at removing most harmful (infectious) particles. The take-away is to avoid, if possible, sitting within a row or two of someone who is obviously sick. You can also decrease your chances of encountering such an individual if you limit your time moving about the cabin—granted easier said than done on a long flight. While you may not always be able to change seats on a flight, you clearly have options when choosing seating in a waiting area or restaurant (See CDC website).

Far and away the most important strategy for staying healthy is to avoid exposure to pathogens that may be lurking the surfaces of seatbelt buckles, latches, touch screens and bins. If after such contact handwashing is not possible, the usual case, then carry and use hand wipes. Use them frequently. Second, avoid touching your mouth, nose and eyes with your hands, especially if they have not been sanitized. You can use liquid hand sanitizer as long as it has at least 60 percent alcohol content; hand wipes, however, are more convenient and practical.

Ideally, people who are sick will decide not to travel out of concern for others. But many travel unaware that they are about to come down with an illness and are capable of transmitting that illness to others. This is why the savvy traveler should use universal precautions at all times. Even so, there is always the child (or adult) standing two feet from you in the airplane who decides to sneeze or cough in your presence. When it happens, you’re pretty much out of luck.

I was reminded of this several days after my flight when I came down with the worst cold I’ve had in years. Sometimes it’s just about luck!

Jim Hyde is professor emeritus of public health at the Tufts University School of Medicine. He lives in Charlotte.

Three reports on air travel and germ exposure
What’s the dirtiest surface on an airplane? The results may surprise you.
Harmful germs lurking on planes and in airports.
Germs at the airport.