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==definition of outbreak by CDC==
*epidemic limited to localised increase in the incidence of disease
*[https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html Epidemic Disease Occurrence - Level of disease]
*Sporadic
**a disease that occurs infrequently and irregularly
*Endemic
**constant presence
**and/or usual prevalence of a disease
**or infectious agent in a population within a geographic area
*Hyperendemic
**persistent, high levels of disease occurrence.
*Epidemic
**increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area
*Outbreak
**the same definition of epidemic, but is often used for '''a more limited geographic area'''
*Cluster
**aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known
*Pandemic
**epidemic that has spread over several countries or continents, usually affecting a large number of people.
Epidemics occur when an agent and susceptible hosts are present in adequate numbers, and the agent can be effectively conveyed from a source to the susceptible hosts. More specifically, an epidemic may result from:
A recent increase in amount or virulence of the agent,
The recent introduction of the agent into a setting where it has not been before,
An enhanced mode of transmission so that more susceptible persons are exposed,
A change in the susceptibility of the host response to the agent, and/or
Factors that increase host exposure or involve introduction through new portals of entry.(47)
==what to do when to investigate an outbreak==
# Communicate findings
==second attack rate(SAR)==
*proportion of individuals who are exposed to an infectious agent who become ill
<math>SAR=\frac{number_of_becoming_ill}{number_of_exposed}</math> ==reproduction number=====basic reproduction number===*average number of becoming ill}{secondary cases caused by a single primary case in a fully susceptible population ===effective reproduction number===*actual number of exposed}secondary cases per single primary case ==time course==*incubation period**followed by symptomatic p.*symptomatic p. *latent (pre-infectious) p.**followed by infectious p.*infectious p. *serial interval**time from <u>illness onset of primary case</u> to <u>illness onset of secondary case caused by primary case</u>*generation time**time from <u>infection of primary case</u> to /u>infection of secondary case caused by primary case</mathu> ==SIR model==*S = susceptible*I = infected*R = recovered*β = transmission coefficient (S→I)*γ = recovery rate (I→R)
