I have held for a long time an erroneous idea of the risk of disease transmission aboard airplanes.I envisioned the passenger cabin as some sort of 3-d Petri disk crammed full of various viruses and other pathogens just waiting for a new host.
An excellent article in the July 2007 issue of Mayo Clinic Proceedings corrected my misconceptions. The editorial " Dealing with threat of Drug-resistant Tuberculosis" written by Dr. Priya Sampathkumar is an excellent review of the basics of drug resistant TB and the quality of air in a plane from a medical point of view and can be found free, full text here.
He tells us that the recommended rate of air exchanges in a hospital isolation room used for TB patients is 6-12 exchanges per hour while modern passenger aircraft have 20-30 exchanges per hour. Further,there are high efficiency particulate air filters that remove 99.9% of particles that are between 0.1 and 0.3 micra. The TB bacteria is about 0.5 to 1.0 micra. More reassurance comes from the fact that air enters and leaves the cabin at the same seat row there being little flow from the front to the back of the plane. Of course, all of this assumes everything is working as it should and as always anything that can work can break down. The cases of TB that have been linked to in-flight exposure apparently all occurred in persons who were seated within 2 or 3 rows of the patient.