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March 21, 2018

How to avoid germs on a plane, according to new research

Daily Briefing

    A study published Monday in the Proceedings of the National Academy of Science finds that the overall risk of catching a respiratory illness from fellow airplane passengers is low—but there are certain things you can to cut your risk of infection even further.

    Infographic: The germs on a plane—and how to avoid them

    The study, published in the Proceedings of the National Academy of Science, was conducted by researchers from Emory University and the Georgia Institute of Technology, in collaboration with Boeing.

    Study details

    For the study, 10 researchers boarded a total of 10 flights, all of which were Boeing 757s or 737s, going back and forth from Atlanta and the West Coast. In each flight, the researchers seated themselves in pairs—with one researcher on each side of the aisle—about five to seven rows apart and took notes on how passengers moved around the plane's economy-class section. 

    Based on those notes, the researchers identified several patterns of movement:

    • Passengers in aisle seats or middle seats were more likely than those in window seats to move during the flight. According to the researchers, 57% of window-seat passengers remained in place for the whole trip, compared with 48% of middle-seat passengers and 20% of aisle-seat passengers;
    • Of the 1,296 passengers across the 10 flights, 84% had "close contact" with another passenger seated more than 1 meter away. According to the researchers, the average number of such contact was 44, with each encounter lasting about 24 seconds (for a total of between 18 and 98 minutes spent in encounters with other passengers); and
    • Flight attendants spent an average of 67 minutes in contact with passengers per flight, accounting for about 1,149 "person-minutes" for the typical flight (compared with about 206 minutes of contact with other members of the crew).

    The researchers then used the data to enact multiple simulations to explore how a virus would spread if a crew member or passenger—seated in various test locations—was sick. To keep their calculations conservative, the researchers said they based the simulations on a transmission rate four times higher than an actual event in 1977, when 38 of the passengers and crew on a plane with 54 individuals became ill with influenza-like symptoms after the plan was forced to remain on the tarmac for 4.5 hours.

    Key findings

    Overall, the researchers found that when a passenger was ill, the individuals most likely to contract the illness were located in the seats next to, in front of, or immediately behind the ill passenger—but the risk for each flight's passengers as a whole was low.

    For instance, the researchers ran a simulation in which the ill passenger was seated in seat 14C (an aisle seat) and found that while passengers in rows 13,14, and 15 had "high" odds of contracting the illness, the odds of anyone else on the flight catching the illness was less than 0.03. In fact, based on that simulation, only 0.7 additional passengers would become ill over the course of the flight—and even in the worst-case simulations involving an ill passenger, the researchers said only two individuals contracted an illness based on their exposure to that passenger.

    However, when the researchers ran simulations in which a crew member was ill, the odds of contracting the illness substantially increased because the crew members interacted with so many passengers. Overall, the researchers estimated that an ill crew member would infect an average of 4.6 passengers. For those simulations, the researchers relied on a lower transmission rate based on the assumption that crew members were unlikely to "come to work while being extremely sick" and that if they did, they "would be more likely to take medication to reduce or eliminate coughing."

    Overall, however, passengers seated in window seats were less likely than those in middle or aisle seats to catch an illness, the researchers concluded, since those in window seats come into contact with fewer passengers and are less likely to leave their seats. The "window seats are a little less risky than the aisle seats," Vicki Hertzberg, co-lead author on the study and a biostatistician at Emory University, said. "I have always chosen window seats. But after this study, I have stopped moving around as much on flights."

    Study limitations

    According to the researchers, the findings are only applicable to transcontinental flights on planes that have three seats on either side of a single aisle. Passengers on shorter or longer flights, or those on planes with different seating configurations, would likely move around in different patterns, the researchers explained, which would affect transmission rates.

    The researchers added that they studied only transmission by droplet, such as via a cough or sneeze—not "virus-laden particles," which they said could travel farther than droplets and remain longer on surfaces (Doucleff, "Goats and Soda," NPR, 3/19; Kaplan, Los Angeles Times, 3/19; Sweeney, Sacramento Bee, 3/20).

    Infographic: The germs on a plane—and how to avoid them

    Download this infographic to learn about both the obvious and less obvious locations where germs on planes are rampant.

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