Describe the chain of infection and two common ways to break it.

• A. Chain: agent, reservoir, portal of exit, mode of transmission, portal of entry, susceptible host; break it with hand hygiene and appropriate PPE.
• B. Chain: reservoir, agent, portal of exit, mode of transmission, portal of entry, susceptible host; break it with vaccines.
• C. Chain: agent, portal of exit, reservoir, mode of transmission, portal of entry, susceptible host; break it with hand hygiene and isolation.
• D. Chain: agent, reservoir, portal of exit, mode of transmission, portal of entry, susceptible host; break it with antibiotics.

Answer: (A)

Understanding how infections spread helps you see how to stop them. The chain of infection starts with the infectious agent, which resides in a reservoir, leaves through a portal of exit, is transmitted by a mode of transmission, enters through a portal of entry, and finally finds a susceptible host. Breaking this chain means interrupting transmission or exposure. Hand hygiene reduces the chance that pathogens are picked up or spread via hands, cutting transmission at the source or along the pathway. Using appropriate personal protective equipment creates a barrier between you and the infectious agent, preventing exposure during contact with patients, surfaces, or fluids. These two measures are widely taught because they directly interrupt the spread from source to susceptible host. Other options either shift the sequence or rely on treatments or strategies that don’t address the immediate transmission link, such as antibiotics or vaccines, or focus on isolation as a broader control that isn’t the pair listed here.