In the chain of infection, the portal of entry is:

• A. Any body opening through which pathogens enter the susceptible host
• B. Portal of exit
• C. Causative agent
• D. Mode of transmission

Answer: (A)

In the chain of infection, the portal of entry is the route by which a pathogen gains entry into a susceptible host. This is defined as any body opening through which pathogens enter, such as the nose, mouth, eyes, urethra, vagina, rectum, or through breaks in the skin or mucous membranes. That is why this option is the best: it directly matches the concept of an entry path for pathogens entering a person who can be infected. By contrast, the portal of exit is how the pathogen leaves the host (like coughing, sneezing, blood, or other bodily fluids). The causative agent is the microorganism causing illness, and the mode of transmission is how the agent moves from one person to another (direct contact, droplets, airborne, vehicles, vectors). Understanding this helps you focus on protecting entry points with proper hand hygiene, PPE, and barrier precautions to prevent infection.