Prevalence

Prevalence represents the total number of existing persons with a disease or event in a defined population at a specific time. Existing cases includes both old and new cases. Point prevalence refers to the total number of persons with the diseases or event at a specific point in time, while period prevalence represents the total number of persons who had the diseases during a certain period. Point prevalence answers the questions: how many people currently have the disease? While period prevalence answers: what was the disease burden in a given population at a certain period? You can think of prevalence as a pool or a container where new cases (incidence) are introduced and stays there until death or recovery.

Measuring the frequency of diseases or events in a certain population can be conducted using different measurements. Prevalence rate is an important measurement and is calculated by dividing the total number of cases or persons who have the event by the population at risk of having this event. Prevalence rate is obviously a proportion. The formula for calculating prevalence rate is, were K can be 100, 1000, etc”. Sometimes the term prevalence is used instead of prevalence rate. Usually it means point prevalence.

An example of determining prevalence: a village of 50 households was selected with a population of 150 people; every household was visited and an interview accompanied with blood tests was conducted; the number of persons with diabetes was 30. The prevalence rate was calculated to be P= (30/150) ∗ 100= 20 percent.