Unit
- Infectious agent: The pathogen (bacterium, virus, fungus, prion) must be present in sufficient quantity and virulence to cause disease. Understanding the agent's characteristics informs control strategies such as isolation or disinfection.
- Reservoir: A place where the pathogen lives and multiplies, including humans, animals, equipment, and the environment. Identifying reservoirs helps target cleaning and monitoring efforts.
- Portal of exit: The route by which the pathogen leaves the reservoir, such as respiratory droplets, blood, or wound drainage. Barriers at this point, like masks or gloves, prevent spread.
- Mode of transmission: How the agent moves from reservoir to host, through direct contact, airborne particles, fomites, or vectors. Interrupting transmission is a core infection control goal.
- Portal of entry: The site through which the pathogen enters the host, often mucous membranes, broken skin, or medical devices. Aseptic technique and wound care protect these sites.
- Susceptible host: An individual with insufficient immunity to resist infection. Factors include age, underlying conditions, and immunosuppression. Vaccination and nutrition reduce susceptibility.
- Chain interruption: Breaking any link in the chain prevents infection. For example, hand hygiene blocks transmission, sterilization removes agents from equipment, and prophylaxis protects hosts.
- Clinical application: Healthcare workers routinely assess the chain to choose appropriate precautions. A patient with pneumonia requires droplet precautions to break transmission, while a surgical site infection prevention targets portal of entry.
- Standard Precautions: These are the minimum infection prevention practices that apply to all patient care, regardless of infection status. They include hand hygiene, use of personal protective equipment, safe injection practices, and respiratory hygiene. Standard precautions are foundational to breaking the chain of infection.
- Transmission-Based Precautions: Additional measures used for patients known or suspected to be infected with highly transmissible pathogens. Categories include contact, droplet, and airborne precautions, each requiring specific barriers and room ventilation to target the mode of transmission.
- Hand Hygiene: The single most effective measure to prevent healthcare-associated infections. It involves cleaning hands with soap and water or alcohol-based hand rub before and after patient contact, after touching contaminated surfaces, and before aseptic procedures. Proper technique and compliance are critical.
- Environmental Cleaning: Regular cleaning and disinfection of surfaces and equipment reduces reservoirs and transmission. High-touch surfaces like bed rails, call buttons, and doorknobs require frequent disinfection. Selecting the correct disinfectant and allowing proper contact time ensures pathogen inactivation.
Terminology
- Infection
- The invasion and multiplication of pathogenic microorganisms in a host, causing tissue damage and immune response.
- Colonization
- The presence of microorganisms without clinical symptoms; the host may carry the organism and transmit it.
- Pathogenicity
- The ability of a microorganism to cause disease, determined by its virulence factors and the host's defenses.
- Healthcare-associated infection (HAI)
- An infection acquired in a healthcare setting that was not present at the time of admission.
Quick Revision
- The chain of infection comprises six links: agent, reservoir, portal of exit, transmission, portal of entry, susceptible host.
- Breaking any link prevents infection transmission.
- Common reservoirs include patients, staff, equipment, and the environment.
- Healthcare workers must identify the most practical link to break based on the pathogen and setting.