You may have heard about the man with an extremely drug-resistant strain of tuberculosis who took two transatlantic flights, and the health scare that has ensued. The passenger, who had been advised against but not forbidden to travel, was on Air France flight 385 from Atlanta to Paris on May 12, and returned on Czech Air Flight 0104 from Prague to Montreal on May 24. He was found in New York and is now in isolation in Atlanta. For the most current information, check Google News.
Health officials are searching for other passengers on the flights, especially those seated near the infected passenger. The stakes are high in this situation because the strain of TB is rare and difficult to treat.
I checked on the Centers for Disease Control's (CDC) website, and found a ton of information about in-flight disease transmission. It says the risk of transmitting TB though air circulation is low because the HEPA filters on "newer commercial aircraft" (that's in quotation marks because there's no explanation of how new a plane has to be to qualify) are the same type used in hospital respiratory isolation rooms, and the number of times air is cleaned each hour exceeds the recommendation for hospital isolation rooms.
However, even if the air filters are hospital quality, there's no escaping the passengers wedged in around you, the ones whose first-hand germs you're exposed to just by proximity, and that's why it's so important to find the passengers of these flights.
I learned that lesson in a far less serious way on what I now look back on as the most uncomfortable flight of my life. I sat next to a woman who was sweating and coughing the entire 10-hour flight from San Francisco to London, who left her used tissues sitting on the tray table, and whose feverish head lolled onto my shoulder more than once after her Sudafed kicked in. When I got sick two days later and spent the majority of my trip achy and seriously congested (cold medicine and Ibsen don't mix, if you were wondering), there was no question about where I'd picked up the illness.
Should you want to educate yourself, or just freak yourself out (depending on your temperament), the CDC has plenty more statistics and information about air and cruise ship travel health.