As someone who lived the better part of 25 years on airplanes--mostly on foreign airlines or over-the-oceans on US carriers loaded with foreigners--there are no places more dangerous for picking up bacteria or viruses. Every single year I went thru four or more bouts of bronchitis and a half dozen day-and-a-half feverish virus battles. I also landed in the hospital for 8 days with an odd strain of pneumonia I picked up either in India or the Caymans or on flights to & from. And I always did all I could to not pick up anything. It's the closed in space with all the coughing & sneezing, along with the unknowns from all the food etc.
Of course the upside to all that is I have only had one cold and nothing else since quitting that gig in 1999. I'll never fly again and have flown very few times ever since--mostly to Hawaii, so for all you Singer-lovers, I just may live to 110.