Prevalance.

Prevalence in Epidemiology.

Prevalence is the proportion of all cases, old and new, of a particular disease at a given point in time or over a period of time in a given population.

It is a proportion, not a rate or ratio.

It can be determined from cross-sectional studies.

Types:

Point prevalence is the prevalence at a point in time. Usually, prevalence is point prevalence unless otherwise specified.

Period prevalence is the prevalence over a period of time.

Prevalence is always expressed in percentage.

Prevalence = (Number of all cases of a specified disease at a given point in time/Estimated population at the same point in time) x 100

It is useful to determine the magnitude of health problems.

• Prevalence depends upon incidence and duration.
• Prevalence = Incidence x Mean Duration
• Longer the duration of the disease, greater the prevalence.
• In acute diseases, prevalence will be lower than incidence.
• In chronic diseases like TB, prevalence will be higher than incidence.
• If a new treatment for a disease is effective, incidence does not change but prevalence decreases as duration of disease decreases.
• If treatment only prevents death but doesn’t cure the disease, it may cause a paradoxical increase in prevalence.