Which components comprise the chain of infection?

• A. Infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host.
• B. Infection site and symptoms only
• C. Hand hygiene and sterilization
• D. Antibiotics and vaccines only

Answer: (A)

Understanding how infections spread requires recognizing the chain of infection: six interrelated components that must be present for transmission to occur. The infectious agent is the pathogen that can cause disease; the reservoir is where that pathogen lives and multiplies; the portal of exit is how it leaves the reservoir; the mode of transmission is how it moves to a new host; the portal of entry is how it enters the next host; and the susceptible host is someone with a reduced ability to fight infection. Each link matters because breaking any one of these links stops transmission. The other options describe outcomes or interventions rather than the components that make up the chain itself—infection sites and symptoms are manifestations, hand hygiene and sterilization are control measures that can disrupt transmission, and antibiotics and vaccines are treatments and preventive tools that do not, by themselves, define the chain’s structure.