Basically, humans who have succumbed to the virus. They appear to be mostly male, dressed in ragged clothing and carrying a melee weapon (a pipe or ax).
1st Stage Infected behave in a brutish, unitelligent way. They will charge the player on sight, slowly at first, often speeding up as they are shot. When they have closed distance, they will initiate a clumsy attack with their weapon will can be easily dodged, but can cause a fair amount of damage if it connects. Sometimes they will attempt to throttle the player, initiating a Quick-Time event. A successful response will throw the Infected off Hayden, whilst failure will result in a crushed neck. They are surprisingly resistant to damage and will attack in groups, swarming the player in typical 'Zombie-esque' fashion. Engagement with firearms at a distance is recommended, but a shotgun will work wonders in CQB situations. Should they sustain enough damage, the Infected will glow red, allowing a finisher to be performed.