It's transmitted like a disease - that much was clear from the progression
before Collapse. The easiest way to get it is to come into contact with an
Infected. Some caveats to that, however:
If you *do* catch it, you should be able to tell long before you go hunting for kidneys. There are obvious symptoms - your heart rate goes way up, to around 140, and stays there - this will shortly give you a 30's-wino-look, splotchy red nose and cheeks. You also start to feel pretty awesome...your pain sensitivity goes down, you're stronger and faster. These symptoms *never* take longer than 3 hours to show up after your initial Exposure...so if you got tagged 4 hours ago and aren't blooming, you can relax and change your pants now.
Somewhere between 24 and 28 hours after Exposure, things go completely south - you immediately lose most of your higher brain functions, and go bat-shit crazy in the Infected flavor (see below, re: Behavior). You are *not* infecti*ous* until this point - so even if you're Exposed, you're not going to pass it on until you actually flip the crazy switch (unless, I suppose, you gave someone an actual blood transfusion or something retarded like that).
To date, nothing anyone has tried has un-Exposed someone, and lots of things fail to "prevent" it. Here's
a list of things which may or may not make you feel better, but are confirmed to not be helpful wrt. Exposure/Infection:
First and foremost - Infected are not actually zombies, ok? In practical terms, they're maybe about as intelligent as an ape or a chimp - they can use and understand simple tools, but most moving parts are beyond them - they may club you with a shotgun, but they'll never pull the trigger. Important exception to this: *They do get fasteners - door knobs and crash bars, and car door handles*.
I'm going to break the rest down into two different "modes", because they are quite different. "Wandering", which seems to be the default state, and "Rage".
Normally they just shamble around, essentially randomly unless something catches their attention. There's a list (see below) of what those things are, most of which trigger Rage (see below). The ones that don't are basically food - anything obviously edible that isn't alive, they'll purposefully go over and try to eat it, until they get full, then they just drop it and wander away. "Obviously edible" includes colorfully-packaged dry or wet goods - apparently consumer conditioning runs deep. They'll try to bash open cans or jars, but not with much skill. While wandering, an Infected will not vocalize at all - they don't grunt, they don't moan. Maybe they breathe hard if they're doing something, but that's about it. Eventually they appear to get sleepy, and just lie down wherever they happen to be for some Z's, but they never seem to sleep for more than an hour at a time. [anyone with reliable data on how long they can go without sleep, post it on the forums]
This is where they want to kill whatever triggered them. Note, I said *kill*, not eat. Sure, they'll eat you afterwards when they go back to wandering...you're just meat then. But when they Rage they want to kill you as directly and efficiently as possible. So they usually don't bite, it's more punching/choking/clubbing/etc. You can tell an Infected is Raging because it will be vocalizing loudly (this varies, screeching is the most common), and running *very fast* towards whatever it wants to kill, or in the process of killing it. They'll keep on until they succeed - and they are not bears, they do not get bored...curling up in a ball will not save you. They *may* switch targets, however, if something else seems to be a better (i.e. more active?) one. Once everything's definitely dead, they go back to Wandering.
Investigate Triggers (they'll go over and check it out, but not Rage):
Notice Triggers (they might look around to try to visually identify these, but they don't specifically
"investigate", nor immediately come for them with death in their eyes):