Which of the following statements best describes the chain of infection?

• A. Portal of exit and portal of entry are necessary for transmission
• B. Transmission is not required for infection
• C. Reservoir does not contribute to spread
• D. Agent is not needed for infection

Answer: (A)

Understanding the chain of infection hinges on how a pathogen moves from one host to another. For infection to occur, the pathogen must exit its current reservoir through a portal of exit and then enter a new host through a portal of entry. These two steps are essential for transmission; if either exit or entry is blocked, the pathogen can’t reach a new host, and infection cannot spread.

For example, a respiratory virus is released from an infected person’s mouth or nose and can be breathed in by someone else, entering through the respiratory tract. The other statements conflict with this process: infection requires transmission to a host, the reservoir does contribute to spread by harboring the pathogen, and an infectious agent is needed to cause infection.