outbreak

n. eruption, explosion (usually of an unpleasant thing)

Outbreak is a classification used in epidemiology to describe a small, localized group of people or organisms infected with a disease. Such groups are often confined to a village or a small area. Outbreaks may also refer to epidemics, which affect a region in a country or a group of countries, or pandemics, which describe global disease outbreaks.
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Noun
1. a sudden violent spontaneous occurrence (usually of some undesirable condition); "the outbreak of hostilities"
(synonym) eruption, irruption
(hypernym) happening, occurrence, natural event
(hyponym) epidemic

(n.)
A bursting forth; eruption; insurrection.
  

    breakout