germ jets

Apparently on the airplane I caught some kind of death cold. It's really unpleasant. I cough like I'm about to produce a lung at any moment, and my voice sounds like an angry mouse who smokes three packs a day. I totally felt this sore throat coming on during hour four or five of the flight back, but I had hoped it was just temporary.

Can I just ask one question? Why is it that air on airplanes is recirculated? Isn't the plane surrounded by air? Fresh, germ-free air? Wouldn't it be a relatively simple matter to say, let a little bit of the air into the plane? I know it's all pressurised and stuff, but still, we can send people to the moon, you think they would've figured out a way to let some air into an airplane.

Anyways, I'm going to go lie in bed and cough for five or six hours now. 'night.