Every infection prevention strategy is designed to interrupt a transmission route. Understanding how infections travel is the foundation of understanding why every infection control measure exists.

Section 01

The Chain of Infection

Infection requires six links in a chain. Breaking any one link prevents infection:

  • Infectious agent: The pathogen — bacteria, virus, fungus
  • Reservoir: Where it lives — human body, soil, water, surfaces
  • Portal of exit: How it leaves — cough, wound drainage, stool
  • Mode of transmission: How it travels — contact, droplet, airborne
  • Portal of entry: How it enters — mouth, wound, respiratory tract
  • Susceptible host: A person with insufficient immunity
Section 02

Contact Transmission

🤝

Direct contact

Pathogen transfers directly from infected source to host — skin to skin, contact with a wound, body fluid contact. MRSA, C. diff, VRE primarily contact-transmitted. Prevention: gloves, hand hygiene, gowns for contact precautions.

📦

Indirect contact

Pathogen transfers via contaminated intermediate — door handles, bed rails, equipment, caregiver hands. Most healthcare-associated infections involve indirect contact. Prevention: environmental cleaning, hand hygiene at WHO Moment 5, equipment disinfection.

Section 03

Droplet vs. Airborne Transmission

Droplet

  • Large particles (over 5 microns)
  • Travel up to 6 feet, fall quickly
  • Don't stay airborne
  • Examples: influenza, COVID-19, pertussis
  • Prevention: surgical mask within 6 feet

Airborne

  • Small particles (under 5 microns)
  • Remain suspended in air
  • Travel beyond 6 feet
  • Examples: TB, measles, varicella
  • Prevention: N95, ventilation
Section 04

Vehicle Transmission

💡 Vehicle and vector transmission
Vehicle transmission: Through contaminated food, water, medication, or equipment. Foodborne illness (Salmonella, E. coli) and waterborne illness are examples. Prevention: safe food handling, sterile medications.

Vector transmission: By insects or animals — mosquitoes (malaria), ticks (Lyme disease). Rarely relevant to direct patient care but important for clients in endemic areas.
Section 05

Breaking the Chain in Home Care

✓ Every infection control measure breaks a chain link
  • Hand hygiene: Breaks the mode of transmission
  • PPE: Breaks the portal of entry
  • Environmental cleaning: Eliminates the indirect contact reservoir
  • Isolation precautions: Contains the agent and reduces portal of exit
  • Vaccination: Eliminates the susceptible host
You don't need to break all six — breaking any one prevents infection.
Knowledge Check

Lesson 1 Quiz

5 questions · Passing score: 80%
Question 1
The chain of infection can be broken by intervening at:
Question 2
MRSA is primarily transmitted by which route?
Question 3
The primary difference between droplet and airborne transmission is:
Question 4
A caregiver touches a client's bed rail then touches the client's food. This is:
Question 5
Hand hygiene primarily breaks which chain link?