When to Escalate
How Infection Moves from Source to Host
Transmission requires six linked conditions: 1. Infectious agent: The pathogen capable of causing disease, such as a bacterium, virus, fungus, or parasite.
Transmission requires six linked conditions: 1. Infectious agent: The pathogen capable of causing disease, such as a bacterium, virus, fungus, or parasite. Its quantity, virulence, and ability to survive in the environment influence transmission. 2. Reservoir: The place where the agent lives and multiplies. A reservoir may be a symptomatic patient, an asymptomatic colonized person, an animal, contaminated water, equipment, or another environmental surface. 3. Portal of exit: The route by which the agent leaves the reservoir. Examples include respiratory secretions, blood, stool, urine, wound drainage, vomitus, and shed skin cells. 4. Mode of transmission: The way the agent travels. Transmission may occur through direct contact, indirect contact with a contaminated object or surface, respiratory particles, a contaminated vehicle such as food or water, or a vector such as an insect. 5. Portal of entry: The route into the next host. Common portals include the respiratory tract, mucous membranes, nonintact skin, the gastrointestinal tract, and tissue exposed through an invasive device. 6. Susceptible host: A person who lacks enough protection to resist the agent. Immune status, age, pregnancy, vaccination status,...