In the chain of infection, the portal through which a pathogen enters a new host is called

• A. Pathogen
• B. Reservoir
• C. Portal of Exit
• D. Portal of Entry

Answer: (D)

This item tests understanding of how a pathogen enters a new person. The portal of entry is the route by which the pathogen gains access to a susceptible host—through a break in the skin, the mucous membranes of the eye, nose, or mouth, the respiratory tract, the gastrointestinal tract, or other entry points. It’s the path the organism takes to establish infection in a new individual.

For example, inhaling respiratory droplets brings a virus into the lungs, while a cut in the skin can allow bacteria to penetrate. In contrast, the pathogen itself is the microorganism, the reservoir is where it lives and multiplies, and the portal of exit is how it leaves the current host (like coughing or bodily fluids). The mode of transmission describes how it travels between hosts (air, contact, fomite, etc.). Recognizing the portal of entry helps explain how prevention works, such as protecting entry sites with barriers, masks, or hand hygiene.