Many people think they get sick after flying in an airplane, but is it their imagination or are germs really worse on a plane? We wanted to know just how dirty planes are, so we sent our i-Team into the air to find out.

This topic touched such a nerve that just a few months ago the flight attendants own union put out a warning. This warning came after two mumps patients traveled on a number of flights, possibly spreading the disease. We tested four airlines and found only one passed our test.

Sure we see plenty of nasty behavior on board the flights, but we wanted to know what might be there that can't be seen, and our results could make you sick. Microbiologist Kelly Reynolds says, "Most of the surfaces tested on these airlines would fail what I call my hygiene test.'"

We took flights on four different airlines: Delta, Southwest Airlines, U.S. Airways, and Mesa Airlines. On each trip we swabbed areas that most people come into contact with: the seat, seatbelt, armrest, tray table and the attendant call button. Then we packed the samples in ice and mailed them off to the lab at the University of Arizona.

Kelly says, "We found the samples collected on the plane were heavily contaminated with general bacteria." Of course, there's bacteria in every public place and anything below 1,000 bacteria is considered normal, but most of the areas we tested registered off the charts.

"One site in particular was the call button, so that tiny little button you press to call the flight attendant we found over a hundred thousand bacteria," said Kelly. That's more than a thousand times what you'd expect to find!

Andie Abkarian is not your typical airline passenger. She flies enough that she knows to carry hand sanitizer on board. Andie says, "It always crosses my mind. What... what could be on that button or on that arm rest?"

Andie's not the only one. "I'm constantly washing my hands and that's all we can really do," said one flight attendant. This flight attendant has worked with two different airlines over the last 10 years. "Oh you see food on the floor. I've seen people put diapers in the seatback."

What's disturbing is there is no regulation when it comes to planes being sanitized top to bottom, making the airplanes traveling germ factories. Kelly says, "Airplanes could serve as sort of a transition route between different areas geographically for spreading germs."

U.S. Airways proved to have the lowest germ count on a single flight according to our test. In a faxed statement the airline said, "We ... clean our aircraft, including overhead bins, tray tables, armrests and lavatories with disinfectant after every flight."

Scott Camacho of Southwest Airlines says, "Southwest does what's called a maximum effort cleaning." Southwest Airlines was second in the test. Scott Camacho represents the only airline that would go on camera to address our results. "The aircraft is scrubbed down from the ceiling to the carpet every thirty days."

Delta airlines took third in our test with extremely high bacteria, and the worst was Mesa Airlines. That flight maxed out the test at over 100,000 bacteria with every swab sampled. Neither Delta nor Mesa would comment.

Airline customers are left to wonder what other germs might be flying the friendly skies. Andie says, "Knowing that, I probably would be much more careful about pouring out a little snack."

The good news is that none of the tests came back positive for e-coli or staph, but if a surface has a lot of bacteria, you are a lot more likely to pick up a virus. The best thing you can do to protect yourself is simple: bring a bottle of sanitizer or even wipes on board, and clean off the area you come in contact with.