Research published on March 19 in the Proceedings of the National Academy of Sciences found that passengers seated within one row and within two seats laterally of someone with a common infectious respiratory disease had an 80 percent or greater chance of becoming infected. For everyone else on the plane, however, the risk of infection was less than 3 percent. “We were interested in how infectious disease might spread from one person to another via large-droplet transmission,” says the study’s first author, Vicki Stover Hertzberg, PhD, of Emory University in Atlanta. “You’re coughing or you’re sneezing or maybe you’re talking, and those large droplets get emitted. What we found was there was this limited perimeter where people had the greatest risk. For passengers seated outside of that perimeter, there was a very low probability.”
Why a Window Seat Might Be Better
The study also found that where a passenger sits correlates to in-flight behaviors that can raise the risk for infection. Passengers seated on an aisle were far more likely to travel about the plane’s cabin, increasing their potential exposure to germs throughout the cabin. Eighty percent of travelers in an aisle seat moved at least once during flights, whereas 62 percent of passengers in middle seats and only 43 percent of passengers seated by a window got up. The most common reasons that passengers left their seats were to use a lavatory and to check the overhead bin.
Passenger and Flight Attendant Risk
While the risk of being infected by a fellow passenger was relatively low, the chances of catching something from a crew member was much greater. The study found that one sick passenger, on average, infected 0.7 additional travelers. But one sick flight attendant can infect an average of 4.6 passengers. On an approximately four-hour flight, each crew member was in contact with passengers for 67 minutes and averaged 155 minutes in the galley. “We found that people in aisle and middle seats were at an increased risk, but the infectious crew was more likely to infect other crew members,” Dr. Hertzberg says. “Flight attendants spend a lot of time together in galleys.”
How the Study Was Conducted
The FlyHealthy study, funded by Boeing, was conducted between 2012 and 2013. The study team recorded the movements of passengers and crew members in the economy class cabins of 10 flights between Atlanta and five West Coast destinations. Eight of the 10 flights occurred during flu season. The team also collected 229 environmental samples of the air and surfaces such as seat-belt buckles and lavatory door handles in the economy class cabins. The surfaces were sampled for 18 common respiratory viruses, including influenza, rhinovirus, and coronavirus. “Those samples all happened to be negative,” Hertzberg says. “What that tells me possibly is that the airplane environment is pretty clean.” While previous studies have documented person-to-person transmission of infectious disease on flights, Hertzberg says no studies have attempted to create statistics on the risk of transmission. “The two big messages are that respiratory viruses are spread through close contact and the inanimate environment plays little, if any, role,” says William Schaffner, MD, an infectious diseases specialist at Vanderbilt University in Nashville, Tennessee, who was not involved in the study.
Study Limitations
Questions do remain about the spread of infectious disease on airplanes, Hertzberg admits. While most of the research was done during a flu season, it was not an especially severe one like this year’s. Also, all the flights tracked were with the same airline. Studies conducted at another time or on different flights, such as transatlantic or transpacific flights, might yield different results, she says. Still, the findings should reduce some anxiety about being exposed to infectious diseases during air travel, Hertzberg says. “I hear people say, ‘Oh I get so sick on airplanes.’ But I wonder how much of that is recall bias,” she says. “People tend to focus on airplanes. You don’t recall you were also standing on the subway platform or in line at the hotel or in the boarding area, ready to board. There are lots of places along the path of taking a trip from point A to point B that might allow for transmission.” “We strongly feel if you are observing good hygiene — hand washing, using hand sanitizer and keeping your hands away from your face — that should be pretty good protection,” she adds. Another good strategy, Schaffner points out, is always to get a flu shot each year.
