Chain of infection notes

Chain of infection (six links, in order):

• Infectious agent: the pathogen itself, for example MRSA bacteria.
• Reservoir: where the agent lives and multiplies, for example a colonized patient or a contaminated surface.
• Portal of exit: how it leaves the reservoir, for example respiratory droplets or wound drainage.
• Mode of transmission: how it travels, for example contact, droplet, or airborne.
• Portal of entry: how it gets into the next host, for example a surgical incision or the respiratory tract.
• Susceptible host: a person who can be infected, for example a patient with a weakened immune system.

Where controls break the chain:

• Hand hygiene breaks the mode of transmission link by removing pathogens before they travel from one person to the next.
• Gloves and gowns (PPE) block the portal of exit and portal of entry by putting a barrier between the agent and the host.
• Aseptic technique during a procedure protects the portal of entry so the agent cannot reach a sterile site.

Immune response outline:

• Innate immunity acts immediately and is non-specific: skin, mucus, inflammation, and white blood cells that engulf invaders.
• Adaptive immunity is slower but specific: B cells make antibodies and memory cells form, so the next exposure is met faster.

Key idea: you only have to break one link to stop the spread, so pick the link a control actually reaches.