In the days immediately before I flew home for the winter holidays last year, I was in perfect health, boasting about the strength of my immune system.
It only took a short 3-hour flight, however, for that confidence to fall apart completely.
The day after I'd landed in my home city, I was celebrating my time with family by downing flu medicine and hot ginger tea, and I couldn't join in any conversations at the dinner table due to my croaky voice and sore throat. So what had happened?
Past research has shown that airplanes can be the perfect environment for the propagation of viral infections. One study has concluded that "[c]ommercial airlines are a suitable environment for the spread of pathogens carried by passengers or crew."
However, being exposed to the risk of infection doesn't necessarily mean that we will get ill; if we know where the danger lies, we can take steps to prevent contact with harmful germs.
Researchers from Emory University and the Georgia Institute of Technology — both in Atlanta, GA — recently joined forces to investigate what the likeliest "routes" may be for germs transmitted by someone coughing or sneezing in an aircraft.
How passengers move in-flight
"With over 3 billion airline passengers annually, the in-flight transmission of infectious diseases is an important global health concern," say researcher Vicki Stover Hertzberg and colleagues in a new paper published in the journal PNAS.
But so far, no studies have addressed the trajectories of transmission aboard an airplane, explain Hertzberg and team. The current study aimed to fill that gap by analyzing a model of infection routes between passengers and crew aboard transcontinental flights.
The researchers — who call their team, appropriately, the "Fly Healthy" research team — came up with a "map" of germ transmission by observing the position and movement of passengers and crew during five West Coast round-trips with different destinations.
Four of these round-trips took place "during the traditional 'influenza season'."
The scientists monitored the movements of passengers and cabin crew, noting which people were likely to be most active and how individuals were positioned relative to an ill passenger on board. The researchers also collected 229 air and surface samples on all the flights.
Their observations revealed a detailed "map" of the passengers' in-flight movements, which found that people in aisle seats tend to be more likely to move around. That said, no passengers tend to go about the aircraft for any long period of time.
Therefore, Hertzberg notes that "around 40 percent of passengers never leave their seats, another 40 percent get up once during the flight, and 20 percent get up two or more times."
"Proximity to the aisle was also associated with movement. About 80 percent of passengers in aisle seats got up during flights, in comparison to 60 percent of passengers in middle seats and 40 percent in window seats. Passengers who leave their seats are up for an average of 5 minutes."
Vicki Stover Hertzberg
Keep sanitizer handy!
In terms of how germs are transmitted, the trajectory of infection seems to be fairly steady, overall. Unsurprisingly, the people seated the closest to a coughing and sneezing individual are the most likely to catch the stray germs.
As the researchers explain, "Only crew and passengers within two seats laterally or one row [in front or behind the ill passenger] are likely to be in contact with this passenger, and all other passengers are much less likely to have contact."
Thus, "[They] found that direct disease transmission outside of the one-meter area of an infected passenger is unlikely," says study co-author Howard Weiss.
The most danger may actually come from cabin crew, who move around more often and come into prolonged contact with more passengers.
Regarding the flights analyzed in this study, "each crew member was in contact with passengers for 67 [minutes]," making it likelier that an ill flight attendant will hand out some complimentary germs with your glass of gin and tonic if they're not careful. "An infectious crew member will infect 4.6 passengers," the researchers estimate.
However, the danger of this can be minimized, if, as Weiss advises, "Passengers and flight crews [...] [exercise] hand hygiene and [keep] their hands away from their nose and eyes."
Major hotbeds for germs are actually the surfaces that we come into contact with all the time when aboard a plane, such as tray tables, seatbelt buckles, and bathroom door handles.
So, you would do well to bring hand sanitizer and wet wipes in your hand luggage, as well as give that tray a quick clean before setting your favorite new book on it. Remember: you're in a closed environment with over 200 strangers.
And, if you're the one coughing and sneezing before a flight, maybe have a look at this handy list of six things that you can do to prevent transmission, put together by the Centers for Disease Control and Prevention (CDC).