Epidemiologic Triad

Basic Disease Investigation
Module One: Communicable Disease Basics

Epidemiologic Triad

In order for a disease to be communicable, the disease must be able to be transmitted from an infected person, animal or an inanimate source to a susceptible host. Transmission can occur directly or indirectly, through an intermediate animal, plant or object. The interaction of the following three elements determines the likelihood of disease transmission:

1.	Agent
2.	Environment
3.	Host

The relationship between the agent, the environment and the
host is complex, and is often shown as a triangle (and referred
to as the epidemiologic triangle). If any side of the triangle is
disrupted, disease transmission will likely cease.