The hazard isn’t where you might suspect it is. Mingling in the airport with hordes of travelers—grabbing empty bins in security, touching hand rails on escalators, ordering food at counters, and sitting near the gates—is far riskier than breathing air near someone you hear sneezing or coughing a few rows away.
Airplanes have been designed to pump fresh, filtered air through the cabin ever since the days when smoking was allowed on board. (Otherwise all those planes would have been worse than the smokiest dive bar.) Commercial jets pull in half their cabin air from the high-altitude environment, where it is cold and sterile, while the rest of it is cabin air recirculated through HEPA filters.
Air exchanges occur 10 to 15 times an hour, and the air flows laterally across the row, not from the front of the plane to the rear. Because of the way the air loops, when the Centers for Disease Control and Prevention investigates potential infectious transmission on a plane, public health officers generally contact passengers in a zone just two rows in front of and behind the sick passenger.