They're not zombies.
That's point No. 1 in the developer documentary video above, which shows how Naughty Dog set about making The Last of Us' infected into uniquely terrifying foes. We're totally going to call them zombies--c'mon, they're still contagious, vicious, mindless ex-people--but their idiosyncratic behavior and appearance do a lot to set them apart.
You can try not to breathe in any spores, or let your friends get killed by bandits, when The Last of Us releases for PlayStation 3 on June 14.