The next day, more icky news broke: Two American Airlines flights, one from Paris and the other from Munich, landed in Philadelphia with more reports of passengers with flu-like symptoms. While these flights were not quarantined, passengers were screened by medical teams upon disembarking and the CDC was notified. Just 12 passengers were held for additional screening, though “nobody was very ill,” according to the CDC (paywall).

In an age of anti-vaxxers, ebola, and terrorism, it’s understandable that the paranoid among us are shaken when reports of spontaneous bouts of sickness begin circulating on Twitter. But the cause turned out to be perfectly banal: The CDC reported that those who fell ill were afflicted with the flu or common cold (paywall). The concentration of sickness was due in part (paywall) to the fact that many of the passengers on these planes had been on their way back from the Hajj in Mecca, Saudi Arabia, where they’d been commingling with 1.7 million other pilgrims—and then passing those germs onto other travelers on their journeys home.

“While it’s more common than you might think for an individual passenger to be noted as sick and investigated by port authorities upon arrival, it is pretty unusual for whole flights to be quarantined in that way,” says Jimmy Whitworth, professor of international public health at the London School of Hygiene & Tropical Medicine. “If it was a highly pathogenic influenza or something like SARS, then absolutely you would want to know and you wouldn’t want hundreds of passengers spreading all over the country. As a precaution, that’s the right thing to do—in this case it was a false alarm.”

It’s likely that some passengers boarded the aircraft sick, Whitworth said, while others were incubating already and developed symptoms during the flight. As a general rule, passengers who board a flight healthy probably won’t show symptoms of a respiratory illness until after their flight, as a standard incubation time is about 24 hours. Though he noted gastrointestinal illness can incubate much faster.

Nervous flyers can take solace, then: Public health officials were just doing their jobs. And to avoid your own worst flight ever, get a flu shot before the end of October, wash your hands religiously, and don’t watch any films about pandemics.

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