Epidemiology: Nursing

Epidemiology is the study of factors that determine health-related conditions in a population, including infectious and chronic diseases; accidents and injuries; and the effects of occupational and environmental exposures.

As the nurse, you’ll use epidemiology to identify factors that affect health-related conditions in your community and use that information to reduce disease risk and promote health.

Now, there are some common measures in epidemiology used to describe health-related conditions.

Morbidity is the occurrence of a condition in a population, like the number of individuals who have asthma, influenza, or have experienced a hip fracture from a fall. You can measure morbidity using incidence rate and prevalence rate.

An incidence rate refers to the occurrence of new cases of a certain condition within a population at risk during a specific time.

To calculate an incidence rate, you’ll set up a ratio with the number of new cases as the numerator and the population at risk as the denominator.

Keep in mind that the population at risk is comprised of individuals who are at risk for the condition; so known cases and individuals who are not susceptible to the condition, like those who are immunized against a certain disease, are subtracted from the total population.

As an example, let’s say that in a community of 10,000 people there were 40 existing cases of asthma, and 10 new cases were diagnosed during one year. To find the incidence rate, subtract the 40 known cases from the total population of 10,000 to get the population at risk of 9,960. Then divide the 10 new cases by 9,960 to get an incidence rate of 0.001. You’ll then multiply this number by a factor, like 1,000, to avoid small fractions.

This gives you an incidence of asthma cases per 1,000 individuals in the community, which is 1 per 1,000 during that year.

On the other hand, a prevalence rate, which is also called prevalence proportion, is the number of existing cases of a condition within a population at a specific time.

To calculate a prevalence rate, you’ll set up a ratio with the number of cases as the numerator and the total population as the denominator. Prevalence includes all cases in a given time, meaning both existing and new cases.

So, in our example, for prevalence, there are a total of 50 cases of asthma, composed of 40 existing asthma cases, plus the 10 new asthma cases diagnosed over the course of the year. To find the prevalence rate of the community, divide the 50 asthma cases by the total population of 10,000.

This gives you a prevalence rate of 0.005. You'll then multiply this number by 1,000 to get the number of asthma cases per 1,000 individuals in the community, which is 5 per 1,000 during that year.