Prevalence
What is prevalence?
Prevalence is the proportion of people in a population who have a disease or health condition, either at a particular time or over a period of time. Because it is a proportion, its value is between 0 and 1, where 0 means no one has the condition and 1 means the whole population has it. It can also be expressed as a percentage between 0% and 100%, or as the number of cases per 10,000 or 100,000 people.
There are two main types of prevalence: point prevalence, which refers to the number of cases at a particular time, and period prevalence, which refers to the number of cases over a defined period of time.
Why should we calculate it?
Prevalence is useful for describing the distribution of a disease, determining how common it is in a population, and generating hypotheses to explain its occurrence. It is widely used by epidemiologists, health policy makers, insurers and public health professionals in general.
Did you know that…
Prevalence is calculated by dividing the total number of cases of a disease by the total population.
It quantifies the proportion of people in a population who have the disease at a given time or over a given period and helps to estimate the size of the health problem within a population.
Incidence vs. Prevalence
It is important to note that prevalence is not the same as incidence. While prevalence measures all existing cases of a disease at a given time, incidence refers to the number of new cases that occur during a given period.
A long-standing disease that is widespread in a community in 2024 will have a high prevalence in 2025, but may have a low incidence rate if no new cases are detected. In this way, prevalence is a useful parameter for long-term infections, such as HIV infection.
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