Veterinary Epidemiology and Zoonosis

INCIDENCE

• Incidence is the number of new cases that occur in a known population.
• There are two components, the number of new cases and the period of time over which the new cases occur.

 

Incidence Rate	=	No. of new cases of a disease which occur in a population during a stated period of time —————————————————————————————————————— Average no. of animals in that population during the same period of time X length of time period	x	100
Area Incidence Ratio	=	No. of new cases of a disease in a given time period ————————————————————————————————————— (Unique geographical area in which observations are made) x (Time)
Zoonosis Incidence Ratio (ZIR)	=	New cases of Zoonosis in an animal species at a time in an area —————————————————————————————————— Average human population at that time in that area

Cumulative incidence rate

• Also termed as risk. It is the proportion of non diseased individuals at the beginning of the period of the study that become diseased during that period.

Relationship between incidence and prevalence

• Prevalence depends on the duration (D) and the incidence rate (I) of the disease, then P = I x D. A change in prevalence can be due to change in incidence rate, change in the average duration of the disease and change in both incidence rate and prevalence.