Incidence of a disease


The incidence of a disease is, in epidemiology, the measurement of the new cases that appear of a certain disease. That is, the accounting of new registered infections of a certain disease.

In this sense, we speak of incidence when the appearance of new cases of a disease in a country, region or geographical area is observed, in a specific period of time (generally one year).

In this sense, if the population in question registers 10 new infected during a week and this population has one million inhabitants, we will say that the incidence of this disease is 1 new infected per 100,000 inhabitants. In the same way, we can say that the incidence of the disease in said territory is 0.001%.

Importance of the incidence of a disease

There are pathologies with a greater presence due to genetic and consanguineous components and, therefore, linked to genetic issues. That is why there is a higher incidence of certain diseases in certain regions or countries than in others. Hence the importance of knowing the probability of occurrence.

On the other hand, in the case of a pandemic, it can be analyzed in terms of its probability of occurrence, records of patients who suffer from it, and its spread. This is the incidence of it.

However, the data that emerge from the studies of the incidence of a disease are usually used by epidemiologists, those responsible for health policies, international organizations, insurance agencies, among others.This, in order to assess the impacts, risk factors, care and even its prediction regarding the number of people affected and the adoption of preventive measures.

Difference between incidence and prevalence of a disease

It is particularly important to avoid confusing incidence with prevalence.

In this sense, we are talking about two very different measurements. Well, while the prevalence focuses on the number of people who have a certain disease during a period of time, the incidence focuses on the new cases that a certain disease registers in a certain population.

Therefore, the prevalence expresses the existing infections and that are present in the territory. While, on the other hand, the incidence shows the new infections that are registered and that, therefore, show the new damage registered by said disease.

Calculation of the incidence of a disease

To know the incidence in a population, the number of cases of sick people must be known, as well as the number of people that make up the total population.

Once we have that, we can use the following formula:

I = CN / PR


I = Incidence of a disease.

CN = Number of new cases of sick people.

PR = Population at risk.

It is necessary to bear in mind that an observation period must be set. In addition, we must consider that, initially, people did not have the disease.

Another significant element to take into account is the fact that a dynamic population can exist, that is, when new people are added to the population. For example, as a product of immigration, or if people leave for migration. This is particularly important as it will have an effect on proportions and hence incidence.

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