Incidence and Prevalence

Incidence:

Definition:

The number of new cases emerging in a specific period and area

OR

The number of new cases occurring in a defined population during specific period of time

Incidence= Number of new cases of specific diseases (during a given time period     × 1000

                     Population at risk during the same interval

Incidence demonstrates about:

·         New cases of the diseases during a specified period of time in a specified population and area

·         Incidence is not influenced by the duration of the disease

·         The of incidence is restricted to only acute diseases

Cumulative incidence:

CI = Number of disease people           × 100

        Total number of healthy people

Attack rate:

A.R. = number of disease people   × 100

            Number of exposed people

Prevalence:

The number of existing cases occurring in a defined population during a specific period of time

The term disease prevalence refers to all the existing cases in a specified area and in a specified time.

Prevalence = Total number of individuals having attribute or disease at a particular time

                        The population at risk of having the attribute or disease in a particular time

Types of prevalence:

         i.            Point prevalence: specific to days, month, age or sex

       ii.            Period prevalence: specific to period of time such as from July 2010 to July 2011