Koch's phenomenon


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Koch's phenomenon

Etymology: Robert Koch; Gk, phainomenon, anything seen
a tuberculin reaction that occurs when a culture of tubercle bacilli is injected into the skin of subjects already infected with the disease. In humans a positive tuberculin reaction indicates sensitization resulting from a tuberculosis infection. Also called Koch's reaction.

Koch's phenomenon

A local inflammatory reaction resulting from injection of tuberculin into the skin of a person who has been previously exposed to the tubercle bacillus. The test represents the clinical application of a type IV (delayed-type) hypersensitivity reaction. In contemporary skin tests for tuberculosis, Koch's, or “old, ” tuberculin has been replaced by tuberculin purified protein derivative. See: tuberculosis