Outbreak definition: If there is an outbreak of something unpleasant , such as violence or a disease, it... | Meaning, pronunciation, translations and examples outbreak meaning: 1. a time when something suddenly begins, especially a disease or something else dangerous or…. Outbreak definition, a sudden breaking out or occurrence; eruption: the outbreak of war. B. The definition of an outbreak will vary according to the phase of measles control. Occasionally, an outbreak is seen in a population for which the cause is unclear. Definition of a measles outbreak. break (out′brāk′) n. 1. Learn more. For more information on what to do in a pandemic, call the CDC Hotline at 800-CDC-INFO (800-232-4636) or go to www.cdc.gov. See more. Read more on disease outbreaks of unknown etiology. NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. A sudden increase: an outbreak of influenza. 2. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Such an outbreak may be due to a new or modified pathogen, a natural toxin, or it may be due to an initially undetected release of a chemical agent or over-exposure to ionizing radiation. A sudden eruption; an outburst: "an outbreak of strikes, violent agitation, and arrests" (Samuel Chew). Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. This guide recommends two different definitions for measles outbreaks depending on whether the country has conducted nationwide catch-up SIA’s or not.