How a Virus Spreads Through an Airplane Cabin

March 21, 2018

Traveling by plane greatly increases our chances of getting sick, or so many of us are wont to believe. To be fair, it’s not uncommon to come down with a nasty illness after we return from a vacation or business trip. But is flying the culprit? The latest research suggests the answer is no—but much of it depends on where we sit.

New research published today in Proceedings of the National Academy of Sciences suggests that airline passengers infected with influenza—a disease that spreads through the air—aren’t likely to infect other passengers who sit more than two seats to the left or right, or more than two seats in front or back. In other words, your chances of contracting the flu from an infected passenger are slim—unless you’re sitting within about three feet (one meter) of them.

Given that three billion of us fly annually, combined with the popular conception that we often contract diseases inflight, it’s surprising to learn that very few studies have looked into this issue in detail. Tracking the spread of viruses on planes, it seems, isn’t easy. Tools like video cameras, RFID tags, ultrasound, infrared, and other technologies normally used to track human movements cannot be used in an airplane cabin during flight for safety and privacy concerns, frustrating efforts to study transmission patterns of disease on flights.

“As far as we know, nobody had any quantitative understandings of the movements, behaviors or social contacts between individuals during flight. We also haven’t seen any studies of testing cabin air and swabs of surfaces for respiratory viruses,” Howard Weiss, Georgia Institute of Technology mathematician and co-author of the new study, told Gizmodo.

To study how infectious diseases might spread during flights, Weiss, along with co-author Vicki Stover Hertzberg from the Nell Hodgson Woodruff School of Nursing at Emory University, devised and tested a new observational technique which used paired observers (members of the research team) seated every five rows, each using an iPad app, and later aggregating these local “zone-by-zone” observations to chronicle all movements of passengers and crew within an airplane cabin. “We are proud of the success of this method,” said Weiss.

Armed with this protocol, the research team tracked the movement patterns of passengers and crew in single-aisle aircraft over the course of 10 intercontinental flights, eight of which took to the skies during flu season. For the purposes of this study, the researchers were primarily concerned with influenza, a respiratory infection which spreads via droplets (aerosols) through the air. Using this data, Weiss and Stover Hertzberg developed a model that allowed them to determine likelihood of infection during flights; importantly, the researchers did not track the spread of the flu per se, instead using pre-established models of influenza transmission. In addition to recording the movements of passengers and crew, the team also collected air and surface samples from areas most likely to host microbes.

“This was the first study to quantify passenger movement, behaviors, and social contacts and to estimate transmission likelihood using a data-driven model,” Weiss told Gizmodo. “The simulations provide compelling evidence that for influenza, if you are not seated within a meter of an infected passenger, and you practice careful hand hygiene, then you are unlikely to get infected during flight.”

In the new study, the authors used the example of an infected person sitting in the middle of the plane. According to their computer models, passengers who sat in the row directly in front or behind, or within two seats laterally (to the left and right), had an 80 percent or greater chance of becoming infected. But for everyone else, that number dropped all the way down to 3 percent. As for an infectious crewmember, they have the potential to infect an average of 4.6 passengers per flight, according to the new model.

Interestingly, of the 229 environmental samples taken on the flights, not a single sample contained traces of 18 common respiratory viruses. Planes, it would seem, aren’t the cesspool of germs we often make them out to be (still, be sure to wash your hands).

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