''Infection'' (2004) (original title: ''Kansen'') is a Japanese horror film directed by Masayuki Ochiai. It is volume one of six in the ''J-Horror Theater'' series, adapted from an episode of the Japanese horror TV series ''Yonimo Kimyō na Monogatari'' entitled "Kyuukan" ("Urgent Patient"), written by Ryoichi Kimizuka and first broadcast in 1991 in Japan.

An understaffed general hospital teeters on the brink of bankruptcy. As night falls, an ambulance arrives at the hospital bearing a patient with a strange black rash, whom Dr. Akiba initially refuses to admit due to the tight resources. While he is arguing with the paramedic, he is alerted to a crisis in room 3, where an unconscious burn patient has somehow fallen to the floor, his vital signs dropping quickly. In the ensuing confusion, an inexperienced nurse administers the wrong drug into his IV, killing him. After an argument, all the staff members present at the incident agree to cover up the error, taking the body to another room and heating it to speed decay and destroy the blood evidence.

However, the patient that Akiba tried to turn away has been left in the hallway and appears to be liquiefying into a strange green goo. Dr. Akai, who had been napping in room 3, suggests the staff study this patient's symptoms, suggesting that the documentation of a new disease could bring good publicity to the dying hospital and pull it back out of its downward spiral. Unsure how much Akai had overheard of their conspiracy, they reluctantly agree. It is not long, however, before this new patient vanishes, and madness and BodyHorror ensue as the mysterious infection spreads to the conspirators.
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!! This movie contains examples of:
* BodyHorror: The unknown infection causes viscous green goo to leak from the ears and mouth of its victims as it liquefies their internal organs.
* ForeShadowing: A senile old woman believes she can see her dead family in mirrors. [[spoiler:At the end of the movie, Akiba hallucinates seeing Dr. Akai in a mirror.]]
* GainaxEnding: The disease [[spoiler:was all in Dr. Akiba's mind]][[RealAfterAll ...or was it?]]
* MeaningfulName: [[spoiler:Akai]] means "Red."
* MedicalHorror: A movie about a highly infectious disease that dissolves people, set in a hospital. Do the math.
* MindScrew: If [[spoiler:the disease was all in Dr. Akiba's mind]], then why did [[spoiler:Dr. Nakazono start seeing green everywhere?]] If [[spoiler:Dr. Akiba was the murderer]], then why did [[spoiler:that other doctor practice sutures on Dr. Kishida?]]
* MysticalPlague: The disease may or may not be [[spoiler:an infectious form of guilt]], depending on some interpretations.
* ThePlague: The eponymous infection.
* PlayingWithSyringes: The rookie nurse likes to practice on patients. [[spoiler:Then she gets infected and starts practicing on herself.]]
* PunnyName: The Japanese title "Kansen" can be written with two kanji which roughly mean "emotion" and "color" - both of which are recurring themes in the film.
* StrappedToAnOperatingTable: More like a hospital bed, when [[spoiler:Dr. Akiba dreams that Dr. Akai injects him with calcium chlorate]].
* ThroughTheEyesOfMadness: Is all this really happening, or is Dr. Akiba going insane?
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