Editing Infection Control and Safety (section)

== The Chain of Infection ==

Infection requires six links. Breaking any one link prevents transmission, and most nursing interventions are best understood as attacks on a specific link.

# '''Infectious agent.''' The bacterium, virus, fungus, protozoan, prion, or helminth capable of causing disease. Virulence, invasiveness, and dose influence whether infection occurs. Nursing and system interventions: antimicrobial stewardship, disinfection and sterilization of equipment, environmental cleaning.
# '''Reservoir.''' Where the organism lives and multiplies: humans (symptomatic patients and asymptomatic carriers), animals, water, soil, food, contaminated equipment, biofilm in sink drains. Interventions: cleaning and disinfection, proper waste and linen handling, treating infected hosts, food safety, water management programs (for example, for ''Legionella'').
# '''Portal of exit.''' How the organism leaves the reservoir: respiratory secretions, blood, stool, urine, wound drainage, breast milk, skin scales. Interventions: cough etiquette, covering wounds, containing drainage, careful handling of soiled linen (hold away from the uniform, never shake).
# '''Mode of transmission.''' Contact (direct person to person, or indirect through a contaminated object or the hands of a healthcare worker), droplet (large respiratory particles that travel a short distance), airborne (small droplet nuclei that remain suspended and travel on air currents), vehicle (food, water, blood, medications), and vector (mosquito, tick, flea). '''Indirect contact by way of healthcare workers' hands is the most common mode of transmission of HAIs.''' Interventions: hand hygiene, personal protective equipment, precautions, dedicated equipment, patient placement.
# '''Portal of entry.''' Broken skin, mucous membranes, the respiratory or gastrointestinal or genitourinary tract, and every indwelling device: intravenous catheters, urinary catheters, endotracheal tubes, drains, and surgical incisions. Interventions: aseptic technique, sterile dressings, removing devices as soon as they are no longer indicated, skin integrity care.
# '''Susceptible host.''' Risk rises with extremes of age, immunosuppression (chemotherapy, corticosteroids, transplant, HIV, neutropenia), malnutrition, uncontrolled diabetes, chronic disease, invasive devices, surgery, prolonged hospitalization, and prior antibiotic exposure. Interventions: immunization, nutrition, glycemic control, sleep and mobility, treating underlying disease.

'''Application note.''' Exam items often describe a scenario and ask which link is being broken. Wearing gloves and a gown breaks the mode of transmission link. Placing a sterile dressing over a wound breaks the portal of entry link. Giving influenza vaccine to staff and patients addresses the susceptible host link. Discarding an open, dated bottle of irrigation solution addresses the reservoir link.