The flu does not fly

Are you the type to worry about catching the flu from a fellow airline passenger? Finding of a new study will comfort you

If you’re the type of traveller who worries about catching the flu or another dreaded disease from a fellow airline passenger, a new study should put your mind at ease.

If a plane takes off with one infected flier, it is likely to land on the other side of the country with only 1.7 infected fliers, researchers found.

What you really need to watch out for is a flight attendant with a cough or runny nose. A single one of them can infect 4.6 passengers during a transcontinental flight.

A group that dubbed itself the FlyHealthy Research Team came to these conclusions after flying back and forth from Atlanta to the West Coast in the US on 10 flights and paying extremely close attention to the movements in the economy-class portion of the cabin.

Ten researchers boarded each flight and spaced themselves in pairs five to seven rows apart, sitting in seats on opposite sides of the aisle. From these prime vantage points, they took copious notes on who went where. Then they recorded each step in an iPad app.

Over the course of the 10 flights – which lasted between 3 hours and 31 minutes and 5 hours and 13 minutes – several patterns emerged:

The seat 14C syndrome

The researchers used all this data to simulate what would happen if a passenger in seat 14C (an aisle seat) were sick. To be conservative, they used an transmission rate that was four times higher than a real-life example from 1977, when 54 passengers and crew were forced to sit on the tarmac for 4.5 hours and 38 of them became sick with an influenza-like illness as a result.

Even under these circumstances, the odds that a single passenger would start an outbreak were extremely low.

For the 11 closest passengers — those seated in rows 13, 14 or 15, in seats A through D — the odds of being infected were “high,” the researchers wrote. But for everyone else on the plane, the odds of being sickened by the person seated in 14C were less than 0.03.

For the plane as whole, the simulations showed that on average, only 0.7 additional passengers would become sick over the course of the cross-country flight.

The researchers repeated their work with simulations that placed sick passengers in other seats. In the worst-case scenario, only two people became infected as a result of their in-flight exposure to another passenger.

Over the 10 flights, the researchers took 229 samples of cabin air and swabs of surfaces like tray tables, seat belt buckles and lavatory door handles. None of those samples contained genetic evidence for any of 18 common respiratory viruses – a striking finding considering that eight of the flights occurred during flu season.

The researchers cautioned that their results could only be applied only to transcontinental flights on planes with a single aisle and three seats on either side. (All of the planes in this study were Boeing 757s or 737s.)

Passengers would likely behave differently on shorter-hop flights or on longer-haul flights from one continent to another. That would affect the disease transmission dynamics in the cabin, as would other cabin configurations with more aisles (and thus fewer seats that are far from an aisle).

The FlyHealthy team also noted that their simulations included only transmission by droplet — cases of germs spreading via cough or sneeze, for instance. They did not try to model the transmission of “virus-laden particles,” which can travel further and linger longer.

Even the most powerful supercomputers have trouble performing the calculations necessary to take these into account, they explained.

Their study was published in the Proceedings of the National Academy of Sciences.


A sick flight attendant was another story, however.

Since these crew members move all around the cabin and get close to so many passengers, they have much more opportunity to spread disease-causing germs. The researchers calculated that one sick crew member would infect 4.6 passengers, on average, even though these simulations used a lower transmission rate.

“A crew member is not likely to come to work while being extremely sick,” the researchers explained. “If she or he came to work, she or he would be more likely to take medication to reduce or eliminate coughing.”

That may seem like wishful thinking, but tests of airplane germiness revealed the cabins were so clean that they were unlikely to have been serviced by sick workers.


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