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Infection Control and Hazardous Materials
Infection spreads only through all six links, so match precautions to the route: contact, droplet or airborne.
Chain of Infection
Infection spreads only when six links connect, a sequence called the chain of infection. The infectious agent (pathogen) lives in a reservoir: a person, contaminated equipment, water or soil. It leaves through a portal of exit, such as a cough, blood, a draining wound or body wastes, and travels by a mode of transmission: direct contact, indirect contact through a contaminated object (a fomite), droplets, or airborne particles. It enters through a portal of entry, such as broken skin, mucous membranes or a catheter, and causes disease in a susceptible host with weak defenses. Breaking any link stops the spread, and hand hygiene, which breaks the transmission link, is the single most important step.