Monday, April 23, 2018

EPI 2.4 Natural History of Disease, Disease Transmission & Epi Triangle

Incidence is the rate of new (or newly diagnosed) cases of the disease.

Prevalence is the actual number of cases alive, with the disease either during a period of time (period prevalence) or at a particular date in time (point prevalence).

The relationship between incidence and prevalence depends greatly on the natural history of the disease state being reported. In the case of an influenza epidemic, the incidence may be high but not contribute to much growth of prevalence because of the high, spontaneous rate of disease resolution. In the case of a disease that has a low (or zero) cure rate, but where maintenance treatment permits sustained survival, then incidence contributes to continuous growth of prevalence. In such cases, the limitation on prevalence growth is the mortality which occurs in the population. Obviously, prevalence will continue to grow until mortality equals or exceeds the incidence rate.

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