What is link three of the chain of infection?

• A. Reservoir host
• B. Infectious Agent
• C. Portal of Entry
• D. Portal of Exit

Answer: (D)

The third link in the chain of infection describes how the infectious agent leaves its reservoir to reach a new host. This Portal of Exit is the route by which the pathogen exits the environment where it lives, enabling transmission. Examples include the respiratory tract releasing droplets during coughing or sneezing, blood from a wound, or secretions coming from mucous membranes. Understanding this step clarifies why reducing opportunities for the pathogen to leave—such as covering coughs, practicing proper wound care, and using barriers like masks—helps prevent spread. This link is distinct from the infectious agent itself and its reservoir, and from the portal through which the agent would enter a new host.