One of the best ways to assure that people pay attention is to endanger a character they love. Sometimes, writers need to be able to put characters in a situation that could potentially result in the (apparently) impending death of multiple characters, but where they can be in a relatively peaceful environment and where death will take a while to befall them. This allows for {{Angst}} and life reassessment.

Enter the ContaminationSituation, in which a main character is exposed to or infected with something very bad, usually potentially fatal and the exposure/infection is a main focus of the episode. In television, unless a character experiences a near-death revelation that completely changes them or dies, these episodes are typically not [[WhamEpisode wham episodes]], but are still usually a big deal. In most cases, we're talking about November/ May sweeps episodes, not season finales.

The infection usually advances CharacterDevelopment by causing the character to rethink their life. In television, typically the person who is infected is involved in a [[UnresolvedSexualTension relationship that seems likely to become romantic]], so you can usually expect a good [[ShipTease moment]] from that couple. This can result in a CrowningMomentOfHeartwarming or, in the best-case scenerio, a LoveEpiphany. If the infected party is not a member of the [[OfficialCouple golden couple]], those two characters will also probably have a meaningful (and shippy) conversation about the fragility of life.

In television, this is most prevelant on crime and medical dramas, not surprisingly. The exposure/infection usually, but not always, happens to a leading character as opposed to a supporting character. A common exception occurs when a lead character's love interest is a supporting character. The goal is for the audience to be emotionally invested, so more often than not, the infected character is a fan favorite.

There are also countless films based on this premise.

!!!!'''All Spoilers will be unmarked ahead. Beware.'''
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!!Examples:

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[[folder: Film ]]

* In ''{{Contagion}}'', Matt Damonís character is infected with a virus, but is immune to it. Later on, one of the main characters has been infected with a virus and uses this to test the cure. Another main character dies from it.
* In ''Film/TheLastManOnEarth'', Vincent Price is the only person left and is immune to the virus turning people into vampires, but does have the virus.
* In ''Film/IAmLegend'', the dog is infected with a virus that turns him into one of the mutants. Robert Neville has to kill his dog.
* In ''Film/TwentyEightDaysLater'', one of the main charactersí friends is infected, and she must kill him.
* In ''TheCassandraCrossing'', one of the main characters, a doctor, is infected with a virus and is considered to be an engineered biological weapon.
* In ''{{Airplane}}'' the mysterious sickness gets both the pilot and copilot.
* In the film ''{{Outbreak}}'', Rene Russo and Kevin Spacey's characters both contract the deadly Motaba virus. One of them lives long enough to get the cure. It is, unfortunately, not Kevin Spacey.
* This is extraordinarily common in zombie movies, and not just to people who [[ZombieInfectee refuse to tell anyone]]. Perhaps the ur-example is Roger in ''DawnOfTheDead'' (Karen Cooper was in a similar condition in ''NightOfTheLivingDead'', but in that example, neither the audience nor the characters knew that a bite always means death). Roger's infection leads to a poignant moment in which he promises to "try...not to...come back."

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[[folder: Literature ]]

* In ''[[Literature/AuntDimity Aunt Dimity and the Lost Prince]]'', Lady Barbara Booker relates how her childhood friend left his stuffed bear at her house the day before he came down with polio (this was in the 1920s, decades before any vaccine). She innocently tried to visit Mikhail to return the bear, and her father "went spare" and gave her a severe spanking. Although she was kept informed of his progress in recovery, "Basha" and "Misha" did not see one another again until Lori ad Bree's investigation prompted Barbara to pay an unannounced visit to Mikhail's family home.

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[[folder: Live Action TV ]]

* ''Series/{{House}}'' had three: "Euphoria" in season two, where Foreman is infected from a patient, "Airborne" in season three, where House and Cuddy are on a plane with someone who is suspected to have meningitis, and Cuddy thinks she has it, and "A Pox on Our House" in season seven, where House is exposed to an contagious patient.
* ''{{Bones}}'' had one in season one ([[ChristmasEpisode "The Man in the Fallout Shelter"]]). The entire team is exposed to an infectious body.
* ''{{Fringe}}'' did theirs in season two. Peter contracts a pathogen at a crime scene.
** In an episode in season one, Charlie becomes an incubator for a supernatural creature.
* On ''[[Series/TwentyFour 24]]'', after Jack contracts a pathogen from a bio-weapon, the entire second half of the seventh season is a string of contamination episodes.
* The penultimate episode of the second season of ''Series/{{NCIS}}'', "SWAK", centered around Tony and Kate's exposure to the pneumonic plague, which was sent to the team in an envelope.
* In the late season four episode "Amplification" of ''Series/CriminalMinds'', Reid is exposed to anthrax by a serial killer.
* In the season four episode of ''Series/{{Psych}}'', "Death is in the Air", a deadly virus is stolen and released on a public place, Shawn then discovers that its part of a PoisonAndCureGambit from the company that makes the cure for the virus, as it was about to be closed down because the government didn't think the virus was a threat enough to fund the cure. The culprit dies before he can release more of the virus, since the cure dosage needed wasn more than he anticipated, but then Juliet gets infected with the virus when recovering the last batch, so they have to race to the culprit's hiding place for the rest of the cure before she succumbs.
* In an episode of ''Series/{{Sliders}}'', one of Quinn's friends gets the plague.
* In ''Series/{{Helix}},'' the series begins in the immediate aftermath of Dr. Peter Farragut's infection with a SyntheticPlague, turning him into PatientZero and the ensemble's TragicMonster, a carrier of TheVirus who spreads it throughout the ResearchInc where he works. The CDC rapid response team includes his brother Alan and his ex-lover Julia, both of whom want to see him saved despite interpersonal tensions and shared estrangement. Peter soon infects Julia, and she in turn, has to cope with realizing her fate and being the sole CDC member in quarantine with other infected.
* ''{{Series/Emergency}}'' had one. John Gage and Dr.Brackett are both infected with a deadly monkey-transmitted flu. Another fireman dies, but the discovery of a person who fought off the virus saves the main characters.
* On ''Series/AgentsOfSHIELD'', in the November sweeps episode "F.Z.Z.T.", Simmons is infected with a virus carried by Loki's soldiers that will eventually cause her to explode, taking the entire plane (and all the other characters) down with her. After apparently failing to develop an anti-serum, she [[spoiler:jumps from the plane in, what is intended to be a HeroicSacrifice.]]

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[[folder: Western Animation ]]

* In ''{{Futurama}}'', Fry has a dormant 20th C. strain of the common cold, which had been erradicated centuries earlier. It leads to the entire island of Manhattan being quarrantined and then launched to the sun for good measure.

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[[folder: Video Games ]]

* In ''ResidentEvil3'', Jill Valentine becomes infected with the T-Virus. It makes her so ill that a second character becomes playable, and it is he who finds a cure.
* In ''TheLastOfUs'', two important characters become fatally infected with Cordyceps. Sam pulls the [[ZombieInfectee usual schtick]]; the other reveals her bite in a bid to guilt Joel into doing what she believes is right.