Disease outbreaks can have major impacts on the health of individuals and communities. They can disrupt socioeconomic conditions and cause disruptions to societal structure and function (see Chapter 15: Disasters). The emergence and re-emergence of new diseases as well as the spread of known ones is typically due to an interplay of multiple factors. The risk of disease transmission can be reduced by ensuring that infection control measures are in place and being implemented.
An outbreak is defined as more cases of a disease than would be expected within a community, geographical area or season. An outbreak can be caused by infectious agents that spread directly between people, through airborne transmission when infectious particles are suspended in the air or via fomites (inanimate objects such as surfaces or clothing) or through vector borne transmission when infections are transmitted by mosquitoes or other insects. The majority of outbreaks are due to known etiologies; however, not all etiologies are solved and some outbreaks have an unknown etiology.
The activities that are applied in managing an outbreak will shift as the outbreak progresses through its phases. The activities that are most relevant at the earliest stages of an outbreak will be epidemiological analyses, whilst control measures apply later in the response phase. There is little evidence that the geographic scale of applicable activities changes as an outbreak develops, although we can see some clustering of different categories of activities at particular geographic scales.
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