Prevalence
disease is defined as follows:
Prevalence =
- Number of cases of a disease present
- in a population at a specified time
- ---------------------------------------
- Number of individuals in the population
- at that specified time<p>
Prevalence is useful because it is a measure of the commonality of disease. It helps
physicians with the probability of certain
diagnoses and is routinely used by
epidemiologists,
health care providers, government agencies, and
insurance companies.<p>
Prevalence is not to be confused with
incidence, which provides a measure of
occurrences of a disease in a specified time interval. Prevalence involves all affected individuals, regardless of the date of contraction.<p>
To illustrate, a disease with a long duration that was spread widely in a community in
2002 will have a high prevalence in
2003 (assuming it has a long duration) but it might have a low incidence rate in 2003. Conversely, a disease that is easily transmitted but has a short duration may have a low prevalence and a high incidence. Prevalence is a useful parameter when talking about long lasting infections, such as
HIV, but incidence is more useful when talking about infections of short duration, such as
chickenpox.
See also:
rare disease
