Tracking the Spread and Burden of Disease: Incidence Rate and Prevalence

Incidence rate and prevalence are two measures that describe the occurrence of a disease or condition in a population.

The incidence rate refers to the number of new cases of a disease that occur in a population over a given period of time.

On the other hand, prevalence refers to the total number of cases of a disease that are present in a population at a given point in time.

Example: Let's consider a population of 100,000 people. At t = 0, that population is known to have 100 cases of a disease. And over the course of one year 100 new cases of the disease are detected. Then the incidence rate and the prevalence are:

• incidence rate = 100 new cases per 100,000 population in a year.
• prevalence = 200 per 100,000 because the total number of cases of the disease in the population at the end of the year is 200.

What's their use?

Incidence rate helps understand the spread (speed) of a disease over time.

Prevalence helps understand the overall burden (stock) of a disease in a population.

Both measures are used to pilot public health policies and to guide interventions aimed at preventing or treating particular diseases.