Sorry to burst the funny bubble.  Since I spent 25 years in the environmental instrumentation field in which one specific area was IAQ (indoor air quality) I learned a few things.  Unless the airlines have changed their ways, the HVAC system in the jets is rarely if ever cleaned.  The cabin is pressurized, of course, so we can be comfortable (more like sane) but that stops the influx of fresh air - that's right, the air just keeps getting recirculated - 100%.  At least office buildings are 80% (energy saving measure).  Our modern office (did it in our church as well) would see the CO2 levels (mental acuity) rise far above recommended levels during the work day or worship service (yawn). So why doesn't everyone get sick (and die).  Well we do have immune systems that can handle quite a bit of poor anything.  If you go on a flight well rested, relaxed and keep your vent closed, you might not get a direct hit from seat 1A who has a nasty cold or worse.  I used to laugh at the people who wore the face masks on flights until I realized how many times I "caught something" in flight.  The air ventilation system in the jets, especially the  little positional nozzle right over your head has probably never been cleaned internally.  I once sat by the window and looked up at the side vent on the jet I was on - filthy - of course, what was I expecting, these jets are run relentlessly.  Sure the cleaning crew comes in and vacuums the seats and the floors daily(?), they might even be using a good antispectic cleaner on plastic parts.  But can you image the time it would take to pull down every nozzle and open every piece of duct work that touches the wall of the jet, yet alone the unreachable parts - face it, it just doesn't happen.  Maybe when they do a complete overhaul and it's out of service for a couple of months - but that's only once in a blue moon (where did that term come from).  So, yes you can get there, less healthy than you started, but not sick.  The longer the flight the more prone you become.  Walk around, keep the body moving when possible - we can get stale (phlebitis) within a few hours.  Beats walking and driving for time, but the airlines could do a lot more for our health.  PS - for those in overdrive - submarines add oxygen to the air without getting rid of the CO2 - maybe airlines do the same. 

[glow=red,2,300]Thank you for being the killjoy of the conversation.[/glow]
Oh, I guess you could take it that way.  Well, let's just say I want Cop to have the very best of time going, being there and returning.  I didn't suggest that he soak a respirator in colloidal silver (great stuff - you know they're putting silver on bandaids and making HVAC duct material with silver in it) and wear it every moment he was on the plane.  Follow some basic guidelines and avoid the worst stuff.  Here's my story time.  I got lucky last Thursday when I has broadsided - wasn't wearing a seat belt - naw - couldn't happen to me!  Now I'll fight for position of my freedom to decide whether or not to wear a seatbelt, but now that I've had to pick myself up off the foot well of the passenger seat, I'll be wearing it a lot more often.  Wear you seat belt - there, any harm done?  Hope it never happens to anyone, but it does - reality's of life.