Morbidity – Concept, prevalence and incidence rate

We explain what is the morbidity or morbidity of a disease and the differences with mortality. Also, morbidity rates.

Morbidity is the frequency of appearance of a disease with respect to the population.

What is morbidity?

In epidemiology and statistics, morbidity or morbidity is the proportion of individuals who contract a disease in a specific place and time frame. In other words, it is about the frequency of appearance of the disease with respect to the population: the higher the morbidity rates of a disease, the greater the number of people affected by it within the period taken into consideration.

This term comes from the Latin word morbidus, which means “sick”, and expressed in percentage terms, it is one of the most useful indicators when planning public health strategies, for example, when dealing with an epidemic. It should not be confused with mortality, a totally different statistical indicator.

Morbidity rates

Commonly, two different morbidity rates are used, depending on the specific information that is needed:

  • Prevalence rate. It refers to the total frequency of cases of the disease, both new and old, that are registered at a given time (point prevalence) or over a period (period prevalence).
  • Incidence rate. Instead, it refers to the speed with which the disease spreads, that is, the rate of contagion or at least the rate of new infections during a certain period of time.

In both cases, the computation of the morbidity rate of a disease is always accompanied by information on the period studied and on the affected geographic region.

Morbidity and mortality

If the morbidity rate refers to the rate at which a disease spreads in a given period and in a specific area, the mortality rate, on the other hand, refers to the number of deaths that occur in a certain area and period.

This mortality can refer either to all deaths, whatever their cause (general mortality rate), or to deaths resulting from a specific cause (particular mortality rate).

Thus, in epidemiology, it is common to study a disease both from its morbidity rate (number of registered cases) and mortality (number of deaths caused by it), in order to get an idea, from statistics, of how lethal what the disease is and how easily it spreads.