The Infected

"I'll see peace back on Earth if I've gotta murder every one of these animals with my own bare hands!"

- Bill

"It's them or us!"

- Coach

The Infected (sometimes referred to simply as Zombies by the survivors) are Left 4 Dead's take on the classic movie and pop-fiction zombie. Rather than being undead, they are living humans who have been Infected by the Green Flu virus, causing massively increased aggression and loss of many higher brain functions such as speech and self-preservation. Like cinematic zombies, those present in the Left 4 Dead series attack human victims until they themselves perish or kill their target.

Characteristics
In the cases of Common and Uncommon Infected, observed aggressiveness manifests itself primarily in the form of frenzied physical blows and kicks. Bite attacks are of a secondary nature and may even be incidentally delivered. The Infected primarily attack uninfected humans who have attracted attention through noise, movement, displaying bright lights, or anything covered in Boomer Bile (whether it be from a Bile Bomb or the Boomer itself). Common Infected are also frequently observed displaying mutual aggressiveness towards one another. However, these attacks cease when the Infected find and focus on an uninfected human.

The Infection might also have changed their physiology. Some Infected suffer severe tissue damage and dismemberment from moderate blunt force, yet they can still jump down from heights of approximately 20 feet with perfect physical coordination and without harm. They have no fine motor control and their gross motor control functions are heavily degraded, thus rendering them incapable of picking up objects and operating simple mechanisms such as door handles.

When passive and unstimulated, Common Infected lean against a support (such as a wall), sit, lie recumbent or stagger aimlessly in short uncoordinated steps. Many will vomit profusely or display visual signs of being unwell (e.g. slumped over cradling the head). The Common Infected have also been observed attacking and killing other Common Infected. The cause of this is unknown. Special Infected and Uncommon Infected tend to be less inert in their passive state since they are invariably observed to be in a standing position.

When active and stimulated, Common Infected display extremely contrasting characteristics, as their speed of movement is rapid, their gait is highly coordinated and their focal direction unerring. Uncommon Infected display the same behavioral qualities with the exception that they appear to be more sensitive to external stimuli and are thus more easily aroused and provoked, with some having abilities to draw other Infected.

Through some unknown mechanism, a small percentage of Infected humans will undergo a dramatic mutation, eventually turning into one of the Special Infected. There are eight varieties of these Infected, seven of which are playable. These eight varieties have special abilities in addition to doing more damage against the Survivors. In turn, two of these eight varieties are considered "Boss Infected", namely the Tank and the Witch.

Common Infected
Common Infected, as their name implies, are the most commonly faced enemy and are the easiest to defeat. They are more akin to the antagonists from the film 28 Days Later than to the typical shambling cinematic zombie. They are exclusively AI-controlled and fairly weak. Their strength lies in their tendency to attack in large groups of up to several dozen, known as Hordes.

However, the danger they pose must never be underestimated. Common Infected can easily bring down health on Expert as every hit drains health by 20 (10 if hit from behind), unlike Easy (1 from front, 0.5 from behind), Normal (2 and 1) and Advanced (5 and 2.5). While they seem capable of ignoring pain, they can still be killed easily. They are capable of climbing ladders and scaling objects, as well as breaking down weak walls and doors. They cannot break down safe room doors, so you should be relatively safe inside of a closed safe room. This type of Infected are attracted by flashlights, loud noises such as car alarms, or by Boomer bile. They appear to lack self-preservation, but do appear to have some intelligence, such as in the Hard Rain or The Passing campaign: the Horde will attack when the storm picks up and there is minimal visibility.

Throughout Left 4 Dead, the physical appearance and dress of Common Infected are consistent with the particular location being visited. For example, in Mercy Hospital, the Infected are medical staff, patients and maintenance personnel, whilst at Metro International Airport, Common Infected include flight, cabin and ramp crew plus business executives. In more neutral locations such as Riverside or Daughtery Farm, Common Infected appear as generic "everypersons, " including servicemen wearing camouflage, blue collar and office workers and young adults through to late-middle-aged individuals of both sexes. The same principle applies throughout Left 4 Dead 2, but given this game's diverse locales, the range of physical variation displayed is considerably wider relative to Left 4 Dead.

Horde
"Here they come!"

- Louis A Horde is a large group of Common Infected (sometimes Uncommon Infected included and rarely Special Infected) that will rush the Survivors either at random intervals, during the finales, as a response to Boomer bile/bile bombs, or in response to loud, high-pitched noises and/or bright lights (car alarms, most other alarms or noises during Panic Events, pipe bombs). Common Infected are weak when alone, but are strong in number. Be alert and prepared when you hear the music cue of an incoming Horde. The Horde can easily bring down any uncoordinated team, especially on Expert.

Uncommon Infected
Left 4 Dead 2 introduced seven special types of Common Infected known as "Uncommon Infected". Each Uncommon Infected is unique to the campaign it appears in (excluding DLC campaigns) and has its own special ability that makes it slightly to moderately more dangerous than Common Infected. Uncommon Infected can also be found in DLC campaigns for Left 4 Dead 2.
 * Dead Center features the CEDA Worker Infected (Immune to flames, improved health, low chance to drop a Bile Bomb when defeated) and Jimmy Gibbs Junior Immune to flames, as tough as a Witch, but can be killed with a headshot instantly).
 * The Passing features the Fallen Survivor (May drop first aid kit, Molotov, pipe bomb or pain pills and has increased health. Their helmet makes it harder to score a headshot, and run away when damaged).
 * Dark Carnival features the Clown Infected (which have squeaky shoes that attract nearby Common Infected).
 * Swamp Fever features the Mud Men (each hit slightly blinds a Survivor's vision, and they also crawl swiftly around on all fours, not to mention they may become hard to spot, but Pipe Bombs can still easily kill a large amount of them).
 * Hard Rain features the Worker Infected (who have earmuffs, so they don't chase Pipe bombs, and only chase Bile Bombs if it hits any infected. The hard hats seem to be only cosmetic, as they don't prevent them from being headshot).
 * The Parish features the Riot Infected (Who can only be killed by attacking them from behind due to their body armor, but it's main weakness is a Chainsaw that instantly kills it, also has a small chance to drop Nightstick).
 * No Mercy and The Sacrifice feature both CEDA Worker Infected and Worker Infected.
 * Cold Stream features both Mud Men and Riot Infected.

Special Infected
The Special Infected have higher intelligence than the Common Infected, as they are not attracted by car alarms or loud noise and are able to run away if required to set up an ambush. They are also more aggressive than the Common Infected, as they will actively attack Survivors rather than passively sitting in a stupor until disturbed (except for the Witch and the Tank, which will wait for the Survivors to alert or attack them). The Director is able to spawn them at almost any time according to the difficulty and how the Survivors are doing.



Seven of the Special Infected are playable by human players in the following gameplay modes:
 * Versus
 * Realism Versus
 * Scavenge
 * Various Mutations

The Boomer
The Boomer is a Special Infected that vomits a special bile at Survivors, which temporarily blinds them and draws a Horde of Common Infected to them. At a distance the Boomer isn't much of a threat; their large size and low health make them an easy target against any weapon at mid or long range. However, if within range, they can vomit on Survivors, attracting the Horde.

When they die, they explode, covering any Survivors who are close enough with bile, blinding them and causing them to stumble backwards. The Boomer is notorious on the Expert difficulty for being able to snipe Survivors. Boomers can be anticipated because of the near-constant gurgling they make. In Left 4 Dead 2, there is also a female Boomer, although the gender has no effect on gameplay.

The Hunter
The Hunter is a Special Infected that has the least visible mutations, and can be mistaken for a Common Infected. The Hunter is absurdly fast and agile, capable of quickly scaling walls. Additionally, he can pounce and pin down Survivors, clawing at their abdomen until either the victim is dead or the Hunter has been knocked off or killed by another Survivor. Hunters are not the most physically robust Infected, having relatively low health, and thus it doesn't take very much to kill them.

When the Hunter crouches down in preparation to pounce, he growls, giving himself away to any nearby Survivors. However, whilst standing, he makes no noise. The Hunter is the only Special Infected that can remain absolutely silent. In Left 4 Dead 2, they can be killed with a melee weapon while in the state of pouncing by aiming upwards and hitting, although this is fairly difficult, as timing is vital and it's easier to kill them from a distance with a high-powered primary weapon.

The Smoker
The Smoker is an ambush class that can strangle Survivors with their long tongue, similar to Half-Life ' s Barnacle. The help of another Survivor is required to escape from a Smoker's hold (There's a short delay before it starts to drag you, during which a shotgun blast may kill it in easy, and doing so successfully grants an achievement). As the name implies, Smokers emit smoke when killed to impair Survivors' vision.

A Smoker also will frequently cough, letting the Survivors know when he is in the area. The Smoker can drag players that he has captured with his tongue towards himself, though he remains stationary and cannot move. The Smoker is also momentarily paralyzed for a few seconds after having his tongue removed from his captive by another Survivor. In Left 4 Dead 2, the Smoker has six tongues, the addition seems to be cosmetic.

The Tank
The Tank is the biggest and strongest of all the Infected and is reasonably fast, only slowing if hit with large amounts of automatic weapons fire or when lit on fire (Versus in Left 4 Dead only and any mode aside Versus on Left 4 Dead 2). He is the only player-controllable "Boss Infected." If any Survivors at 40% or above health (including health gained from pain pills or the Adrenaline Shot) are running away from the Tank, it will not be able to catch them, as they can run slightly faster (unless the Tank in question is an AI Tank in Left 4 Dead, which can catch up).

The Tank has incredible strength and resistance―his punch can send Survivors flying, rendering them temporarily defenseless, and in Expert mode, instantly incapacitate them. The blow can send Survivors off high hazards to their deaths. He is also capable of throwing chunks of concrete that he rips out of the ground to momentarily stun Survivors, dealing the same amount of damage as a punch would. He can also punch large objects (e.g. a car) in the direction of Survivors with enough force to incapacitate them instantly. The fact that the Tank is absurdly tough and it's terrifying amount of damage, combined with its extreme mobility, makes it hard to take out without teamwork or strategies.

Nevertheless, the Tank will die within 30 to 45 seconds if set on fire (varying with the difficulty), except in Versus. When controlled by a player, the Tank has a "Control Meter"; unless the player is able to locate and hit one of the Survivors, the Control Meter of the Tank will slowly lessen, and once it runs out, the player will lose control of the Tank to another randomly assigned player or eventurally, an AI. When idle, the sound that a Tank makes is heavy breathing. The Survivors are alerted of an approaching Tank by dramatic music, furious roars and, when they are dangerously close, the screen will start to shake.


 * The Tank's music cue.

The Charger
The Charger is a Special Infected that appears in Left 4 Dead 2. The Charger's main attack is charging forward and plowing into the Survivors, hence the name. On a successful charge, he will grab and carry a single Survivor while knocking down the others. Once the Charger has hit a wall or other surface, or after he has run a certain distance, he will begin slamming his captive into the ground (and also into the wall and the ceiling if there is one) until an ally frees them. If he misses and hits a wall, he will stumble for a few seconds and becomes vulnerble. If a Charger smashes into anything when not grabbing a survivor, he takes 2 damage instead and is stumbled for 1 second.

The Charger can be detected by the Survivors by the warped growling noise he makes. He will announce his charge with a loud bellow. The Charger appears to have a rocky or calloused surface on his larger right arm, which is what he uses to inflict most of his force when charging, while his other arm appears to have no bones or muscle, flopping around uselessly.

Because of his hulking size, the Charger cannot be shoved off with melee, and must be killed in order to release his victim. If a Survivor has explosive rounds, they will dislodge the Charger from the Survivor and cause him to stumble. Any Survivor that has been knocked out of the way during his charge will fly a considerable distance and slowly stand back up, making the Charger a deadly foe in cramped hallways or near high passageways, but not in open areas. He is also the third strongest special infected — with a whopping 600 health, only losing to the Witch's 1000 and the Tank's 3000; additionally, his melee attacks are very strong and can easily incapacitate a weakened Survivor.

The Jockey
The Jockey is a Special Infected that appears in Left 4 Dead 2. He is a small Infected that attacks Survivors by clinging to them from behind and literally riding the Survivor while attacking them. He can shift his weight around and cause the Survivor to stumble in his desired direction, giving this Special Infected a type of control over the Survivor. He will only let go if his victim becomes incapacitated, or if he gets knocked off/killed.

Survivors who are being ridden by the Jockey can attempt to "resist" the Jockey, causing the Jockey to slow and even pause for a second, which allows other players a chance to catch up and knock the Jockey off. Jockeys can ride Survivors into dangerous situations, such as into natural hazards, Witches, or other Infected; a Jockey can also pull a Survivor off a ledge, causing them to become incapacitated, or riding them to their death if they are not resisting. The Jockey seems to have a spinal disease, similar to kyphosis, giving him a hunched appearance. He also has a maniacal laugh (which gives away his location) and is constantly twitching, giving him a sort of hyperactive nature.

The Spitter
The Spitter is a Special Infected in Left 4 Dead 2. She possesses the ability to spit a green ball of acid from long distances, which, upon hitting the ground, will expand into a large puddle and damage any Survivors who make contact with it. After spitting, however, the Spitter is temporarily paralyzed for a second, giving the Survivors a chance to kill her. The Spitter makes these high-pitched noises that gives away her location.

The longer the Survivor stands in it, the more damage the Survivor takes from the goo. This ability allows the Spitter to aid other Special Infected; for instance, if a Hunter pounces a Survivor, a Spitter can spit upon that Survivor, causing even more damage. However, in spite of such a useful ability, the Spitter is very weak in terms of health, so taking out a Spitter is an easy task.

Upon death, the Spitter leaves a similar, smaller kind of puddle that has the same effect on the Survivors. She is one of the most powerful Infected if Survivors are caught standing in her spit, and are too distracted to move quickly due to other Infected or a lack of awareness at damage being dealt. On Scavenge Mode or any finale requiring gas cans, when they are dropped, the spit will ignite them if left in the goo long enough.

The Witch
The Witch generally only appears a few times per campaign, and is passive unless provoked by flashlights, gunfire, or Survivors in close proximity. She is the second "Boss Infected." Pistol fire does not provoke her easily, but it will do only a small amount of damage (in Left 4 Dead 2, causing any damage to the Witch will instantly startle her). She is very powerful, capable of incapacitating and even killing Survivors with one hit. When the Director spawns a Witch, the faint chord of the Witch music will play, allowing veterans of the game to quickly prepare for the "obstacle."

The Witch cries loudly. When nearby, Survivors will mention they hear her and warn teammates to turn off their flashlight. While the Witch can be killed, her high health makes this difficult (at least 1/3 of the easy mode Tank). It is best to avoid her if possible. Witches can be startled if a Survivor stands too close to her, damages her, or shines their flashlight on her from a close to moderate distance. She will also start to growl if a Survivor looks at her through the Hunting Rifle/Sniper Rifle's scope for a long time.

The Witch is very rarely found in small rooms and normally stays off the main route, but has been found in front of safe rooms (or even inside the safe room), doorways, and in the middle of streets. Once a Witch has killed a Survivor or cannot pathfind to her target, she will retreat from the area and despawn. However, in some strange cases, the Witch has been known to kill the closest Survivor to her. This does not usually happen, and when it does, the Witch runs off as normal after killing the Survivor.

Also, if a Survivor blocks the Witch from attacking the Survivor who startled her, she will attack the Survivor blocking her and either incapacitate the blocking player and run away or incapacitate (or kill on Expert or non-easy Realism mode) both the blocking player and the player who startled her. If the Witch is lit on fire (Molotov, Incendiary ammo, Gas can) while she is chasing a Survivor, she will immediately start chasing after whoever burned her.


 * The Witch's music cue.

Wandering Witch
The Wandering Witch appears in Left 4 Dead 2. She is seen only in the daylight hours, aimlessly wandering around and sobbing loudly with her head in her hands. Her constant movement makes The Wandering Witch harder to avoid, but she is also far more introverted and reacts only to direct attacks or physical contact. One can even damage her slightly without startling her. Unlike the sitting Witches, she does not seem to be alerted that readily by flashlights.

In Left 4 Dead 2 ' s Hard Rain campaign, a large number of Wandering Witches have infested an abandoned sugar mill, which the Survivors must traverse to obtain fuel for their rescue boat. The achievement SOB STORY is earned for navigating the sugar mill without startling any of them.


 * The Wandering Witch's music cue.

Known Infected Individuals

 * Carolyn (Zoey's mother): Turned into Common Infected minutes after being bitten.
 * Jimmy Gibbs Junior : Turned into Uncommon Infected (period of time unknown).
 * Lt. Mora : Turned after a few minutes, he was in transition of turning and was still able to hold a gun and speak some English; however, he sees Survivors as monsters (might not have been completely turned).
 * News Chopper 5 Pilot : Turned into Common Infected in mid-air after rescuing and encountering the Survivors. He was bitten prior to rescuing the Survivors, which resulted in Zoey shooting him as soon as he turned.
 * Sandra : Turns into a Common Infected (period of time unknown).
 * The Church Guy : turns into a Special Infected (Boomer, Hunter or a Smoker) one hour after being bitten.
 * Unnamed Helicopter Pilot (Left 4 Dead 2): Turned into Common Infected in mid-air after rescuing the Survivors, making Nick shoot him.

Screamer
Originally, there was going to be a Special Infected named the Screamer. Wearing a straitjacket, he would run from Survivors, hide, then let out a scream attracting the Horde. However, he was removed because game testers found out that he's extremely hard to locate before he can summon a horde, therefore easily disrupting game balance. His ability was given to the Boomer's bile instead. However, in Left 4 Dead 2, there exists a type of Uncommon Infected called the Clown which can attract a small Horde of idle Common Infected around him with his squeaky shoes. In The Passing, there is an Uncommon Infected referred to as the Fallen Survivor. When shot, the Fallen Survivor attempts to run away, much like what the producers had planned for the Screamer.

Leaker
A Special Infected called the "Leaker" was being developed. It had similar attacks as the Spitter and Boomer, and the ability to plant itself in the ground and act as a landmine. It was removed because the it alerts Survivors with very obvious cues when arming itself, effectively meaning that it can't fight Survivors at all. However, it is still possible to play as the Leaker with console commands by using "Map MAPNAME Versus", then typing in the console "boomer_leaker_chance" and a number between 0 and 1. You will know when you are a leaker if it says "You are a/the Leaker!", or if you explode on death and cause a small fire.