how do you get airborne infection on dirt 3

Codemasters has decided to reveal three all-new gamemodes for Dirt 3’s multiplayer. These modes include Outbreak (An infection-like gametype), Transporter (Capture the flag), and my personal favorite, Invasion, where you have to avert a global disaster by taking out the cardboard robots of doom! Check out all the videos after the jump, including a multiplayer interview with the developers and snow gameplay!