The number of instances of illness commencing, or of persons falling ill, during a given period in a specified population. More generally, the number of new health-related events in a defined population within a specified period of time. It may be measured as a frequency count, a rate, or a proportion. 

Source: Porta M. A Dictionary of Epidemiology. 5th ed. New York, NY: Oxford University Press; 2008. 

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  • incidence