What is the portal of exit in the chain of infection?

The portal of exit is the third link in the chain of infection. The portal of exit is the way in which the infectious agent (the first link) leaves its reservoir (the second link). In humans, an infectious agent can exit the body as drainage, excretion, secretion, discharge, or other substances through systems such as the respirator tract, the gastrointestinal tract, the genitourinary tract, the skin or mucous membranes, the placenta, and the blood.