Which of these is not part of the six links of chain infection?

• A. portal of exit
• B. reservoir
• C. portal of transmission
• D. susceptible host

Answer: (C)

The chain of infection consists of six links: the infectious agent, the reservoir, the portal of exit, the mode of transmission, the portal of entry, and the susceptible host. Each link must be present for infection to spread. The phrase “portal of transmission” isn’t a standard term in this model—the correct term is “mode of transmission,” which describes how the pathogen moves from one person to another (such as contact, droplet, airborne, or vector). So that option isn’t part of the six links. The other options—portal of exit, reservoir, and susceptible host—are all valid links in the chain. Understanding this helps you target infection-control actions to interrupt the spread at the right point.