In the chain of infection, which is link four?

• A. Reservoir host
• B. Portal of exit
• C. Modes of transmission
• D. Susceptible host

Answer: (C)

The thing being tested is how a pathogen moves from one person to another. After the pathogen has a place to reside (the reservoir) and a way to leave that place (the portal of exit), the next step is the route it takes to reach a new person—this is the modes of transmission. These modes include direct contact, droplets, airborne spread, contaminated objects (fomites), and vectors. That’s why the fourth link is modes of transmission: it describes the pathways that allow infection to spread from an infected reservoir to a susceptible host. For context, the other links are the reservoir (where the pathogen can survive and multiply), the portal of exit (how it leaves the reservoir), and the susceptible host (the person who could become infected).