Turning time depends on method of transmission.
6 - 12 hours if infected via bite
12 - 24 hours if infected via spores
24 - 72 hours if infected via food
Stage 1 (1 day - 2 weeks)
Have recently entered their transformation. Still look fairly human. A great way to tell Stage 1 Infected from humans is their glowing red eyes. Stage 1 are extremely aggressive and are known to attack in packs. Their eyesight is poor, but they are still able to spot you almost as good as a human would.
Stage 2 (2 weeks - 6 months)
Begin to grow fungus on their face. Make distinct croaking noises, and late-stage Stage 2 have began to develop a form of echolocation. Stage 2 are known to spot a victim from a distance, and close in on them. Up close, they are just as aggressive as Runners, but slightly stronger. Have completely lost their eyesight by late stage, but still are fairly good at spotting you.
Stage 3 (6 months - 10 years)
Stage 3 have fungus growing out of their head, and are known to make "clicking" noises. Stage 3 are significantly stronger than the average human, but are quite slow. Stage 3 have developed echolocation, and this is their main method of locating prey. Their senses are not as strong as Stages 1 and 2. Due to the fungus growing on their head, they can take 2 to 3 headshots to kill. However, they have a weakness to fire, and can easily be killed with a Molotov cocktail.
Stage 4 (10 years - 20 years)
Stage 4 are by far the strongest and most dangerous stage of Infected, but are very rare, only beginning to appear in the early 1990s. Stage 4 have grown fungus all over their body, are extremely large (7 to 9 feet tall and 400 - 600 pounds) and can take 4 to 6 shotgun shots to kill. The most easy way to kill one is to throw a molotov cocktail at it, and finish it off with 2 to 3 shotgun shots, as like Stage 3, they have a weakness to fire. Their senses are extremely poor, and if you crouch-walk you can easily walk right past them. Be careful, as if you get within grabbing range of one, you are done for! These are extremely slow and can be outran by pretty much anyone, however they can throw Mycotoxin sacs at humans. These sacs are not infectious, but disorient and hurt the human.
When an Infected succumbs to the virus (this usually happens in Stage 4, sometimes in Stage 3) it will find a corner to die in. Its body will grow spores, which will infect the air around it.