Left 4 Dead Wiki
See also: Uncommon Infected

"I ain't gonna let these god damn vampires beat me."
"Dude, those zombies are REAL. I knew them books were nonfiction."

Common Infected (referred to in The Parish and The Sacrifice comic as Whiskey Delta, meaning Walking Dead, by the Military) are the most frequently faced members of the Infected, and the easiest to defeat. Their strength lies in the fact that they attack in groups, more commonly referred to as a Horde, sometimes as large as several dozen.

While they can be killed in the sameways as any human, they possess immense endurance, capable of ignoring missing limbs, high falls, and even a few gunshots if not hit in the head. They are capable of climbing ladders and scaling objects once they find a target, and will not stop until it is dead. The default number of Infected that the Director spawns in a Horde is around 30. These Infected are fast, sensitive to loud noises and movement, and able to attack in ravenous waves, as determined by the Director. They might not notice the Survivors right away, but when they do, they will attack relentlessly until they are killed or manage to kill the Survivors.

Official Description

Meet the zombie horde: eerily fast, sensitive to loud noises and movement, and able to attack in ravenous waves. They might not notice you right away, but when they do, watch out—they're fast, and it won't take long for them to close the distance.[1]

Appearances and Action

Contrary to popular belief, the Common Infected are not "undead zombies," but mutants. Common Infected hair and skin pigmentation are usually very low, resulting in pale gray skin. Lesser Infected may also have pale hair, though some female Common Infected have dark, blond, or red hair. Common Infected come in a variety of appearances of both sexes, such as patients, nurses, construction workers, military personnel, and airport staff, the differences being solely cosmetic if the Infected are not Uncommon Infected.

Fighting Common01

Two Common Infected fighting

When not attacking, they are usually sitting down, leaning on walls, or simply standing. They may also vomit or fight each other, and, when fighting long enough, possibly killing each other. They are easily provoked by light, sound, or touch. The heads, arms, and legs can all be shot or cut off. Common Infected are at least somewhat stronger than uninfected humans, capable of smashing through doors and breaking through walls, and it is very difficult for those caught in their grasp to break free.

The Infected react to gunfire in their vicinity, turning towards the sound to attack the shooter. Usually, if an idle Common Infected receives a non-fatal gunshot wound from a distance, they will writhe in pain and clutch the wound with their hands; if they are running towards the player, they will just continue their pursuit and ignore the pain.

They are often seen engaging in abnormal activities (e.g. vomiting, attacking inanimate objects, fighting each other, leaning on a wall as if exhausted, etc.) when unaware of the Survivors, showing that the sickness may still be affecting them, even in this state, perhaps slowly killing them rather than keeping them alive as Infected. Very rarely, an Infected can be seen facing a wall and making mumbling noises, as if talking to itself.

The methods of attack by Common Infected vary. With normal humans, they bite and claw them apart, sometimes consuming their flesh and other times leaving completely intact bodies behind. These bites are a major method of transmitting the Infection. With the Survivors, they punch, kick, and claw them, though they never bite them. It has been theorized that the Common Infected only bite non-infected persons, which would explain why they also never bite each other, and therefore they will not bite the Infection-carrying Survivors. A simpler theory is that biting was not implemented in the game, possibly due to technical constraints.


A Horde climbing over a fence

The Infected appear to lack a strong sense of self-preservation, as they will actively charge into flames, explosions, jump off from high buildings, and against superior forces of the Survivors and their weapons, even if they have encountered these things before (this can be best observed by throwing a Bile Bomb into a fire in The Hotel). A possibility is that the Infection has affected their brains to such a degree that they only think of spreading it, or may simply think of attacking anything that disturbs them from their vicinity. This could mean that the Infected ignore their injury, only to attack the Survivors.

When approached by a melee-wielding Survivor, however, the Infected frequently dodge or duck from the attacks. The Infected also rigorously make flanking attempts, trying to hit Survivors from the sides or backs as to avoid danger. In addition, they also appear to be capable of many acrobatic actions from contracting the Infection, as they are capable of running great distances and climbing up fences and buildings that humans would not be capable of doing without safety measures in place. They also attempt to trap the player by running up to them from the back and attacking them, slowing the player down, then suddenly going up front to attack compared to behind to prevent the target from escaping easily.

Sitting Zombie

An Infected sitting

The Infected are not known to eat or drink. However, they still survive despite the lack of sustenance. It is possible that the Infection has removed the mental ability to perform these necessary life functions. There is evidence to suggest they occasionally consume their human victims, or even cannibalize each other, though this is rare. This may indicate that the Infected may eventually die of starvation or dehydration, and possibly even exposure to the elements as the Infected do not seem to seek shelter in conditions that non-Infected would. [2]

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A few of the new faces of the Infected in Left 4 Dead 2

According to the game commentary, the developers designed multiple types of faces and bodies, and would have the computer pair them when spawning Infected, ensuring a variety of characters. This allows for "something around 1500 possibilities". Some Infected models can be seen in any scenario of the game, while others, such as the Infected patients in Mercy Hospital or airport customs officers in Dead Air, are only encountered at certain areas. It seems that the Common Infected in Left 4 Dead 2 almost have the same base model, but with changes in hairstyle, clothes, and blood marks. This is to save memory in the second game, so the Pipe Bomb can create ragdolls and the Minigun/50-cal can gib Infected.

Extent of Mutations


An Infected police officer from the original Left 4 Dead

Though the Common Infected have evidently been mutated the least physically by this strain of the Infection, the strain appears to have had a bigger effect on their minds. They seem to have lost many of their higher brain functions. However, their sense of smell and hearing have been greatly enhanced, possibly explaining things such as Crescendo Events and how the Infected are able to find Survivors when they are covered in Boomer bile. It's possible they've had very slight boosts in strength (as hinted by their capability to break walls and take a Survivor down in a few hits on Expert difficulty), speed, and endurance—though, again, it appears to be slight, as they don't withstand many bullets or injuries in general. Perhaps due to loss of higher brain functions, they seem to ignore pain, even when their limbs are blown off. Their eyesight may be extremely poor as an extent of these mutations, as Common Infected can be sometimes seen staring towards the Survivors yet chase after pipe bombs or Boomer bile.

An exception to this is the Fallen Survivor from The Passing, which will run from the Survivors once shot, as opposed to other Common Infected. There seems to be little explanation for this behavior, other than the individual's will to survive surpassed the Infection or that they have a strain of it that didn't affect their sense of self-preservation. However, they still seem not to notice wounds that would be fatal if left untreated, such as a severed limb.

The Infected in general also tend to be incredibly hostile to anything not perceived as being Infected, although there are occasions when two Infected are seen fighting one another and even killing each other. Additionally, the bodies and bones of the Infected seem to have weakened, seeing how their bodies explode with blood when they are shot/chopped, compared with how a normal human being would react, and the fact that a Guitar can decapitate them. Overall, they seem quite animalistic in nature.

If nothing else, they seem to have some grasp of their current situation, or at least how they feel; generally, idle Infected act physically ill, holding their heads and vomiting as they shuffle around slowly. Occasionally, if you watch one long enough, one of the Infected who is holding their head may begin to writhe in pain, or they may simply lie down and sometimes die without being shot or punched, suggesting that the virus slowly kills its host after some time. It is also possible that after Infection, they have a limited lifespan, just like how people infected with rabies (the virus on which the Green Flu is based) have a limited lifespan if left untreated. It could also be through brain hemorrhaging, as Infected appear to bleed out of the eyes, the ears, and the mouth. This would also explain why they hold their heads in pain. Another possibility is that these deaths may be the result of an injury that the Infected person received earlier, such as from a gunshot from other Survivors or from a fall that they endured.

They are shown to have a primitive but working communication system with others, generally through grunts and screams. In The Sacrifice comic, they are also shown to see the Survivors as something inhuman, which may explain why they attack them. It may even be that symptoms of the Infection include immense hallucinations followed by adverse paranoia which leads them to attack nearly anything they see moving, including their own kind on various occasions.

Burned Infected

A set of burned Infected

Ripped Infected

The end result of a close-range shotgun blast

The mutation might have also caused a severe breakdown to human anatomy, as it is observed while killing the Infected. They have their limbs cut off more easily than the normal state, and they burn to death in only a few moments. Furthermore, their bodies become more fragile, making them vulnerable to damage, whether it is an outside force, or internal damage. Melee attacks and simple gunshots do considerable damage to them, even killing them instantly. Also, the anatomical breakdown is also shown in the case that if a Survivor steps on the head of a Common Infected, they will die.

The Horde


Common Infected in Left 4 Dead 2

The "horde" is a term used as a reference to a medium or large group of Common Infected. A horde of Infected can be powerful, but they are not invincible by any means. These hordes can be distracted or dispatched in many ways.

Hordes appear on several circumstances if they have been met:

  • Crescendo Events and Finales: The Survivors usually need to perform an action which generates loud noise to get through in order to reach safety, which will usually attract large hordes of Common Infected.
  • Car Alarms: In some chapters, there are several alarmed cars that, if shot, will attract a Horde. Always use a melee weapon and avoid getting near an alarmed car or you may accidentally set it off by misfiring or hit by a Special Infected.
  • Boomer Bile: If any Survivors are covered in Boomer bile, it will attract nearby Common Infected and summon a horde which will then attack affected players. The same also applies to Infected hit by a thrown Bile Bomb.
    • Pipe Bombs attract nearby Infected to investigate the sounds which accumulate into a small horde.
  • If the soundtrack "Re: Your Brains" is being played on a jukebox, upon reaching the "screaming" segment of the track, a horde will be summoned to attack the Survivors. This is a onetime event and further replays of the soundtrack will not attract a horde.
  • There are occasional small Hordes that occur during quiet periods of the game, known unofficially as "Hurry" hordes. These hordes spawning will occur at random, though typically occur when no Infected are being killed outside a Tank battle, Witch zone, or Crescendo Event/ Finale zone. There is an audio cue when these "Hurry" hordes are summoned, though the horde itself is usually insignificant and can be dispatched within seconds.

Location of Themed Common Infected

In both Left 4 Dead and Left 4 Dead 2, there are special Common Infected that are only found on specific areas or chapters in different campaigns. Unlike the Uncommon Infected, these Infected individuals only look different and do not have any special abilities.

Left 4 Dead


An Infected surgeon sitting on the ground

No Mercy

In the final two chapters of this campaign, the Survivors come across Infected doctors and nurses as well as patients at Mercy Hospital. The hospital staff were trying to treat the Infected individuals; however, they too were Infected.

Crash Course and Blood Harvest

Infected in military fatigues can be seen on these campaigns, especially nearby military equipment or the Farmhouse.

Dead Air

In the final two chapters of this campaign, the Survivors pass through Metro International Airport, encountering several Infected airport staff, such as TSA agents, baggage handlers, and airplane pilots.

Left 4 Dead 2

The Passing

In Rayford Park near The Riverbank, there was a wedding ceremony at the time of the Infection. When the Survivors pass by, the wedding guests are seen wearing their dresses and tuxedos. An Infected Bride Witch can also be seen crying at the altar. Later in the campaign, the Survivors will also encounter Infected bikers and Midnight Riders fans.

Dark Carnival

At Whispering Oaks Amusement Park, there are still members of the park staff seen by the Survivors. When CEDA converted the park into an evacuation center, they were assisting in the evacuation by directing civilians and trying to maintain a level of calmness with the public.

Swamp Fever

There are hillbilly infected in Village En Marais. Common Infected encountered here are covered in mud, instead of blood, and appear to have their clothes soaked. They are not to be mistaken as Mud Men since the mud fully covers this type of Uncommon Infected and they walk on all fours.

Hard Rain

In the town of Ducatel, hillbilly infected make another appearance, and can possibly be mistaken for chargers due to the fact that both of them wear the same type of overalls.

Tactics and Tips

Common Infected are only strong in numbers. Sticking together is key to keeping them off your and your teammates' backs. If you are concerned about conserving ammunition, consider using your secondary weapon, which can be used indefinitely (disregarding the Chainsaw).

It is possible to kill Common Infected simply by jumping on their heads. Survivors can "double jump" if they land on top of a Common Infected's head, allowing them to perform feats that would be impossible otherwise. Since both the Infected and Survivors are of the same height, the Survivor must have a height advantage over the Infected in order to perform this. If the Common Infected is not aware of the Survivors' presence, they may also be melee shoved from the back for an instant kill, obtaining the achievement "SPINAL TAP".

If the Common Infected cannot reach a Survivor or a bile bomb is tossed in an inaccessible area, then they will stay in place, angrily raising their arms in an attacking manner.

Players should ALWAYS be careful of any Infected lying on the ground. If they have been killed already, they should be ignored. However, some Commons tend to lie down, making it look as if they are dead.

Closet Mode

Left 4 Dead 2

The Horde as seen in The Parish

When a Horde is about to attack, an effective strategy is to back into a corner (preferably) or a wall. Assign the front two Survivors to crouch and melee continuously (not viable in Versus or Survival mode in Left 4 Dead) while the two Survivors behind them stand and fire their weapons at the Infected.

Finding the nearest door, closing it, and using a shotgun to blow out a significant chunk of it provides you with a shield that you can see and shoot through, as well as keeping the Infected from touching you—very useful for higher difficulties. The most important thing is limiting the area the Common Infected have to attack. You may also want to throw a pipe bomb to divert the Infected.

Note: This is not recommended for Left 4 Dead 2. This is because the Director will eventually spawn a Spitter or Charger that will force you away from your position. Ultimately, this will bring you out into the open, possibly resulting in the players being surrounded with even more Infected. Also, a patch for Left 4 Dead's Versus and Survival modes (consequently passed on to Left 4 Dead 2 in all modes) implemented Melee Fatigue, which will force a short pause after five rapidly consecutive melee hits, and then after every hit until the player waits a few seconds without shoving after the shove has recharged. The cooldown usually lasts anywhere from one to three seconds. However, Melee Fatigue can be removed for a short period of time by the use of adrenaline.

Remove Loners

Pick off wandering Infected that have strayed away from fellow Infected whenever you can. When entering a new area, swap to pistols or snipe with a Hunting Rifle or a Sniper Rifle to take out as many lone Infected as you can from the entryway. The Director has a tendency to spawn Hordes once you reach the midpoint of areas, and this "event" often causes idle Infected in the area to attack as well. In Versus, however, it is unlikely the Special Infected will allow you to sit in one place long enough to clear a room in this manner, so keep moving.

Removing loners also helps greatly in the event of a Tank or Witch encounter, so they do not slow down the player while they try to flee, avoid or kill the Tank/Witch.

In a safe room, it is often a good idea to stay by the door and pick off any Infected that you can see. They can't hurt you if you're inside, and you can refill your ammo immediately after dealing with them. This can make for an easier exit from the safe room.

Weapon of choice

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Coach and Ellis fighting off Infected in the Parish campaign

Any shotgun can be very useful against the Horde, as their shells deal large amounts of damage and can pass through multiple Infected. The Auto Shotgun and Combat Shotgun are superior to other shotguns, as they chamber a new round automatically every time you fire, removing the delay required to pump the shotgun. A good tactic to use if they are coming through one area, such as a doorway, is to keep your fire directed at the entryway, as the Infected will be clustering together to get through, making them easier to kill. Remember to push the Infected back while reloading, taking into account that the shotgun will take much longer to reload than any other weapon. It is also a good idea to aim low when using a shotgun against smaller Hordes, since gibbing the legs is an instant kill towards Common Infected.

As far as automatic weapons go, rifles can do major damage at any range. The Combat Rifle excels at accurate long-range shooting, but when a Horde is in a player's personal space, it lacks the bullet spread necessary to quickly dispatch a spread-out group of Infected. The AK-47 is the opposite; while it is ineffective at taking out distant enemies, its high power and higher spread can clear out Infected in mid-to-close range with ease. The Assault Rifle has a large clip capacity and the fastest reload speed of any weapon, as well as decent stopping power and good accuracy, making it a balanced and viable choice against large populations of Infected.

The Hunting Rifle and the Sniper Rifle should both be used predominantly to kill distant Infected. If need be, they can be used to kill attacking Infected with their high rate of fire. Keep in mind these high accuracy rifles' notable bullet penetration. If multiple Infected are being funneled through a tight area or are otherwise "stacked" (like when climbing an obstacle), the rifle family can shoot through several Infected with a single bullet. The scoped rifles can, however, instantly kill any Commons the bullet touches, making it useful on harder difficulties (although, on high difficulties in Realism mode, it will take multiple bullets to kill the Infected unless one aims for the head).

However, if the player is swarmed by the Infected, using a melee weapon with good horizontal range such as a Katana should be used as it will kill many Common Infected in one swing. Guns should only be used if there is a fair amount of distance between the Horde and the team, since the attacks of the Common Infected are capable of disrupting accuracy.

Power of the Horde

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Bill and Zoey fending off Common Infected in Dead Air

The Common Infected are especially dangerous on the Expert difficulty. It can only take a couple of hits to incapacitate a Survivor, depending on the Survivor's current health. On this mode, the Common Infected deal much more damage: 20 for each hit on the front, and 10 for each hit on the back. This means that a Horde can easily cripple an entire team if they are not paying attention.

Common Infected can be extremely powerful in their own way, as their attacks are capable of slowing down Survivors and messing up their accuracy. Although it may not seem much, if you are attacked by Common Infected while fleeing from a Tank or Witch, their slowing attacks will allow them to catch up and severely wound/kill the player. Their attacks are usually the result for more than half of the total damage that is dealt to the Survivors during the duration of the Campaign and can easily stack up.

Unlike Special Infected (who are limited in where they may climb), Common Infected are unaffected by this, and will often attempt to flank the Survivors if given the chance. Whenever a Horde spawns, try to find a higher elevation or a choke point. This way, the Horde is funneled and can be easily dealt with so the team does not get swarmed by them and any accompanying Special Infected if they should appear. (Note: If playing Left 4 Dead 2, beware of the Director spawning a Charger or a Spitter to break up your team in a closed choke point.

Darkness is your Friend

L4d matchmakingblog

Infected in the gloom

The Common Infected are obviously known to be attracted by the noise of car alarms and other loud sounds caused by most Crescendo Events, however, most have not realized the flashlight can also enrage Infected. The bright light irritates them, drawing their attention to the player. Flickering the lights on and off will disturb them faster. Using this knowledge may help if two of the Survivors have their flashlights on while the others do not, causing the two with the active flashlights to be targeted by Infected while their partners are able to defend them unimpeded.

In addition, the glare of the flashlight can sometimes cause your vision to focus directly on where the flashlight is pointed. Shutting off the flashlight during a Horde is usually a good idea. Practice using the silhouettes to identify Infected if you use this tactic. In low-light situations, this can drastically improve your ability to see oncoming Infected. Use natural light rather than your flashlight whenever possible to avoid Infected.

Having a flashlight on, regardless in a day or night setting, will aggravate Common Infected. This kind of behavior exemplifies the Common Infected's animalistic traits.

Playing smart

Although Common Infected are easily dispatched, it is still very important to eliminate them when possible and pay attention to one's surroundings. In the event of a Horde or Crescendo Event, communication between players is necessary to avoid Special Infected ambushes and separation. Having a predetermined path and assigned combat roles can all contribute to a successful campaign or versus match. Also, when Infected are near a wall, their shadows can sometimes be seen through the walls, giving you a chance to plan or dispatch them before they become troublesome in a Horde. When a Tank is near, Common Infected could be a significant threat. They will distract you and your teammates, often blocking an escape route and slow them down, allowing the Tank to catch up.

Targeting priority

The Common Infected's targeting priority is:

  1. Thrown Pipe Bombs
  2. Survivors or Infected who are covered in Boomer bile
  3. Thrown Bile Bombs (that are not covering anyone)
  4. Survivors (Only during Hordes, Panic Events, Crescendo Events, Finales, or after they realize Survivors' existence).

Like The Witch, Common Infected will override their priority target if a Survivor is blocking their path. In order to force them to change targets, they must be shoved back.

Brief damage immunity

Upon being hit by a Common Infected, the Survivors have a brief window of damage immunity to another Common Infected attack; the duration of immunity depends on the current difficulty setting. However, if the damage dealt by the Common Infected is equal to or higher than the Survivor's current health, the damage immunity is bypassed and the Survivor will be immediately incapacitated.

Infected tips

When playing as the Infected in Versus, you can use the Common Infected to your advantage. While the Survivors are attempting to reach the safe room, there are many ways you can exploit the Horde. Once the Survivors are occupied by the Horde, a competent Tank can defeat even the most organized Survivor team.

Boomers can not only summon the Horde but also "extend" it by vomiting on the Survivors after they have dealt with the present Horde. Vomiting on incapacitated Survivors is extremely effective and will very often result in death for the Survivor unless someone goes to help them deal with the Horde, as Common Infected will deal 5 times their normal damage against downed players.

Smokers are also effective during a Horde as they can snatch a Survivor and pull them away whilst the others are too busy fighting to help. Smokers can also be protected by Common Infected. If you have snared a Survivor and you pull them in front of you where you can hit them, the Horde will attack along with you, killing them faster. This circle of Infected makes it harder for the Survivors to kill you.

You can even do a substantial amount of damage with a Hunter before the Survivors can deal with the Horde and kill you, as the other Infected will absorb some of the damage that would otherwise reach and potentially kill you. Other Infected will also surround the Hunter to claw at the Survivor.


See Main Article: Achievements

Left 4 Dead

L4d pyrotechnician
Blow up 20 Infected in a single explosion.

L4d my bodyguard
Protect any Survivor from an attacking Infected 50 times.

L4d 101 cremations
Set 101 Infected on fire.

L4d spinal tap
Kill an Infected with a single blow from behind.

L4d zombie genocidest
Kill 53,595 Infected.

L4d red mist
Kill 1000 Infected with a mounted machine gun.

L4d achievement 5359 infected garage
Kill 5,359 Infected in the Crash Course campaign.

Left 4 Dead 2

Burning sensation
Ignite 50 Common Infected with incendiary ammo.

Head honcho
Decapitate 200 Infected with a melee weapon.

Club dead
Use every melee weapon to kill Common Infected.

Chain of command
Kill 100 Common Infected with the chainsaw.

Dismemberment plan
Kill 15 Infected with a single grenade launcher blast.

Using the M60, kill 25 infected without letting go of the trigger.

FORE! (25G)
Knock off the heads of 18 infected with the golf club.

PC exclusive

Achievement Z-Genocidest 2 Episode 2
Kill 53,599 infected. You made sure the dead won't rise anymore!


  • The Common Infected bear a resemblance to the "Infected" in the movie 28 Days Later, as they are not the undead monsters of traditional zombie culture but living people infected with a rabies-like virus.
  • The Common Infected in Left 4 Dead had a much varied appearance in the early build of the game. For unknown reasons, a majority of those skins weren't used for the final build and the others had their textures changed slightly or heavily. These variants were believed to be lost until the release of The Last Stand Update for Left 4 Dead 2, which implemented Left 4 Dead Common Infected from early and final builds into campaigns set in the Northern States.
  • Some Common Infected in Left 4 Dead 2 seem to be a bit rotten in the face as if they are really dead and are decaying. It is possible that this is another symptom of the Infection.
Green Flu victim opening (L4D Survivors)

The Green Flu victim on the opening of Survivors.

  • In the opening video of Left 4 Dead: Survivors, an Asian woman is show transforming into a common infected in a matter of seconds. However, this can't be considered canonical for the mainstream continuity.
  • Children and animals have yet to be seen in the ranks of the Infected. The most likely reason is that if children and animals were in the game, that would mean the player can kill children and animals, which would raise ethical concerns and cause huge controversy.
    • In-game speculation include that it is possible that the Infection is too strong for children and animals, so they die instead of turning into Infected, although birds can be heard in Death Toll, Blood Harvest, and The Sacrifice, crickets can be heard during Dark Carnival, and the barking of dogs can be heard at the beginning of the trailer for Left 4 Dead 2. And in some campaigns, birds can be seen flying (However, Rochelle claims that the virus is spread through mammals, just like rabies, so birds would not be affected).
    • It may also be that there are various animals that are akin to the Survivors in terms of having an immunity to or simply carry the virus, which could explain the reason for the cows in Swamp Fever being burnt.
    • In Blood Harvest, Dark Carnival, and Swamp Fever, dead cows can be seen with the skin removed around their face, indicating a rabies test.
    • The lack of the bodies of children could also be that any Survivors saw it necessary to take the time and give children a burial, or that infected children were removed from the game to avoid criticism, as it would be inappropriate to feature the Survivors killing children.
    • A more brash or radical explanation would be that the Infected cannibalize one another or dead corpses which would remove any corpses from sight. There is significant evidence to the contrary in-game, however, such as piles of untouched corpses throughout The Parish campaign.
  • Sometimes, a glitch occurs where Infected are standing stationary with their arms parallel at 90º (reference position, also called the "T-Pose"). These Infected can be killed, but ragdoll physics do not take effect. Also, these glitched Infected can stop Survivors from moving, and so it has been seen that Survivors can be trapped by these glitched Infected. To rectify this situation, you must restart the server upon which you are playing, or use explosive measures to get past them.
    • A second glitch can occur when one tosses a Pipe Bomb, such as throwing one towards a Horde, and occasionally some Infected may stop moving and glide back and forth, but you are still capable of killing them.
    • In Left 4 Dead 2, sometimes it's possible for the Infected to glitch while trying to climb a pole (either a lamp post or one of the poles in Dark Carnival). The Infected would become completely still and slowly inch up the pole. They would return to normal once they reach the top, or are shot and killed.
  • Sometimes, Common Infected can get stuck in objects, such as tables or forklifts, and become invulnerable to melee attacks and must be shot to be killed.
  • Found in the sound files are clips titled to be belonging to a sort of Infected dog. This could possibly have been a scrapped feature or plans for a future addition. During the 4th chapter of Blood Harvest, it should be noted that howling can be heard in the background, most likely produced from these sound files. However, there is a strong possibility that the file could have simply been applied to the various ambiance that can be heard throughout the campaigns made by idle Infected.
    • The Hunter sometimes makes these sounds when attacking.
  • The voices and sounds of many of the Common Infected were performed by vocalist Mike Patton, who also did the voice of GLaDOS' Anger Core in Portal; (in fact, some Common Infected voices are simply reused from the Anger Core). Additional voices were voiced by Fred Tatasciore and Dee Bradley Baker.
  • When the Infected are summoned in the finales, you hear a scream from them. That sound is a mix of two sounds that can be found in the Half-Life sound folder called "the_horror1" and "the_horror2".
  • Whenever Common Infected are burned in Left 4 Dead 2 (excluding the CEDA Worker Infected), their bodies gain a new texture effect to make them looked charred.
  • In Left 4 Dead, the Common Infected's pupils are hard to see. In Left 4 Dead 2, they seem to have developed reflective areas in the rear portions of the eyes, which glow when a flashlight is shone on them, such as in canines or felines, known as tapetum lucidum.
  • One of the symptoms right before turning into a Common Infected is possibly getting cold, as the helicopter pilot states he is getting really cold before the events of Crash Course, in which he turns into an Infected. This could be caused by the thinning of the victim's blood, which is probably why the Infected and dead bodies have faded skin colors.
    • However, it can be inferred that the pilot was injured by an Infected, which resulted in his subsequent Infection. If the injury was severe enough, the pilot may have been experiencing symptoms of either stage 2 or 3 of Hypovolemia.
  • Previously, there was an unused gore effect featuring a gigantic slash completely down the Common Infected's spine. It is possible that this would've been used (should the Axe had kept its overhead downwards slash) and was used on a Common Infected's back. (The animation for fire ax swinging downwards still exists in the viewmodels animations.)
  • In the Left 4 Dead 2 DLC, The Passing, the Common Infected gained two new models; models for the Midnight Riders fans, models for bikers and models for "formal"-looking Infected at the wedding.
  • Sometimes, Common Infected will attack the ending safe room door even when the Survivors are right next to it. This occurs mostly when three out of all the Survivors are outside the safe room and the fourth is hiding somewhere, such as behind the warehouse shelves at the end of No Mercy's Apartments. This is also possible with Special Infected, but only if the safe room door is inside the room.
  • In Left 4 Dead 2, a Common Infected would usually die when its head is gibbed by a gun. However, on extremely rare cases, it will remain alive without its head and will continue attacking the Survivor whilst headless (more common in the Mutation "Headshot!" as the Commons only die from headshots, decapitations, burning or explosions). This is most likely unintended, however, as a headshot is supposed to be fatal. This most likely is a hit recognition issue.
    • However, there are sound effects that resemble bloody gurgling sounds which are unique to headless Infected.
  • There are no obese Common Infected. This could possibly be from the Infection speeding up their metabolism or heart rate, thus burning up all the body fat.
    • It is also possible that they become Boomers if they are at a certain size or body shape.
  • It is possible to kill a Common Infected just by jumping off a higher ledge and landing on its head.
    • You can also kill a Common Infected by standing on them somehow. For example, it is possible to run over a Common Infected that are lying down and kill them as long as the Infected has not been alerted to the Survivors' presence.
    • Sometimes, by standing over ladders, one can ensure no Common Infected can reach the top of the ladder. For example, in the car impound lot where all the alarmed cars are in The Parish. If one stands over the manhole while the Horde is alerted, any Common Infected coming from the sewers will be stopped by the Survivor up top. Once they hit the Survivor, they will either die or fall back down into the sewers to try and climb up again.
    • With a carefully timed jump and a sizable Horde, one can run across the heads of the Infected and use them like a bridge. However, you can only do this for a short while, since you start to slowly fall after about two steps, and will collide with a Common Infected eventually.
  • Originally when in Versus mode the player was able to take control of a Common Infected while waiting to respawn after being killed as a Special Infected. This was scrapped as it was deemed too difficult for many players to attack the Survivors as they were always competing against AI-controlled Infected.
  • Many finales, such as the No Mercy campaign, do not have a clear reason as to why the Infected come. There is nothing that makes a noise to attract the Infected. It is possible that they can detect radio frequencies, and are attracted to the voices of the Survivors.
    • It has also been suggested by the helicopter pilot that it's like they can sense hope, much like animals can "smell" fear. It's unlikely that he was being serious, though.
  • Prior to The Last Stand Update, in the Left 4 Dead 2 port of No Mercy only the hospital patients from the first game appear among the Horde of Common Infected (no surgeons or nurses), though with far less frequency, and lack of new gore effects; they still have better shadows, however. Unlike their behaviors in Left 4 Dead, their limbs cannot be severed and their heads can be blown off with any weapon (again, also lacking the new effects). Also, unlike other Common Infected in Left 4 Dead 2, knocking their head off will not produce a severed head. However, cutting their heads off with slashing weapons will make a severed head appear, but only occasionally.
    • The original Common Infected's resources existed in the game files for Left 4 Dead 2, as leftovers that were generally unused up until July 27, 2017, when they were added to the L4D1 Co-op and Versus mutations and then added to all the campaigns of the original Left 4 Dead in September 24, 2020, sans the color variation on their clothes as that programming was not carried over to the sequel of Left 4 Dead.
  • There is a glitch when you shoot off an Infected's arm(s). If it is still living, it will attack you with the same animations that other Infected use when they attack with their hands and deal damage, though it has no arms to attack you with.
  • Sometimes, when facing Common Infected, when they notice you they may freeze in their ready to attack position. This is because they have accidentally "noclipped" onto something (like fencing) and cannot move unless they are shoved. However, they still can attack you if you get too close to them.
  • On certain occasions, usually after fighting a horde, a common infected will spawn near the player and will collapse and die the second it's spawned in.
  • A very rare glitch occurs where Common Infected (and their Uncommon variants) may get shoved and get back up, only to get shoved again, even if the Survivors do not shove them. This only works with two or more, as when one is shoved, others nearby will also get shoved back from the main Infected being shoved. Once they get out of this however, they will attack the nearby Survivors.
    • This most often occurs if an Infected is knocked down near a solid object, and bumps into the object while regaining its footing.



  1. The Infected
  2. The theme of the Infected dying out and repopulation commencing is similar to what happened following the events of the film 28 Days Later.

External Links

The Infected
Introduced in Left 4 Dead Introduced in Left 4 Dead 2
Boomer nav Hunter nav Smoker nav Tank nav Charger nav Jockey nav Spitter nav
The Boomer The Hunter The Smoker The Tank The Charger The Jockey The Spitter
Introduced in Left 4 Dead Introduced in Left 4 Dead 2 Cut Infected
Witch nav Common nav Uncommon Infected nav 70px-Screamer nav
The Witch Common Infected Uncommon Infected The Screamer