CHAIN OF INFECTION:
  1. Infectious agent (pathogen): bacteria, virus, fungus, parasite
  2. Reservoir: where pathogen lives (person, animal, environment)
  3. Portal of exit: how it leaves reservoir (respiratory, faecal, blood)
  4. Mode of transmission:
     Contact: direct (touch) or indirect (contaminated surface/fomite)
     Droplet: >5µm particles, travel <1 metre (influenza, COVID-19)
     Airborne: <5µm particles, travel >1 metre (TB, measles, chickenpox)
     Vector-borne: mosquito (malaria, dengue), tick (Lyme disease)
  5. Portal of entry: how it enters new host (respiratory, GI, skin break)
  6. Susceptible host: immune status, age, underlying conditions
  
  BREAKING THE CHAIN: any link broken = infection prevented
  Most effective breaks: hand hygiene, PPE, vaccination, isolation

PPE HIERARCHY:
  Gloves: change between patients, remove without touching outside
  Apron/gown: fluid-resistant, change per task/patient
  Mask: surgical (droplet) | FFP3/N95 (airborne)
  Eye protection: splash risk, aerosol-generating procedures
  
  DONNING (putting on): gown → mask → goggles → gloves
  DOFFING (removing): gloves → goggles → gown → mask (most to least contaminated)
  Hand hygiene after doffing each item

ISOLATION PRECAUTIONS:
  Contact: MRSA, C. difficile, VRE — gloves + gown
  Droplet: influenza, COVID-19 — surgical mask + eye protection
  Airborne: TB, measles, chickenpox — N95 mask + negative pressure room
  
HEALTHCARE-ASSOCIATED INFECTIONS (HAIs):
  CAUTI: catheter-associated UTI — proper insertion, minimal duration
  CLABSI: central line bloodstream infection — sterile technique
  SSI: surgical site infection — skin prep, prophylactic antibiotics
  VAP: ventilator-associated pneumonia — head-of-bed elevation, oral care
  MRSA: methicillin-resistant Staphylococcus aureus — contact precautions

WHY ANTIBIOTICS BECOME INEFFECTIVE:
  Natural selection: bacteria with resistance mutations survive
  Horizontal gene transfer: bacteria share resistance genes
  Biofilm formation: bacteria communities with increased resistance
  
CONTRIBUTING FACTORS:
  Overuse in humans: self-medication, not completing courses
  Agriculture: growth promotion in livestock (now banned in many countries)
  Poor infection control: spreading resistant strains in hospitals
  
RESPONSIBLE ANTIBIOTIC USE:
  Only take antibiotics prescribed by a doctor
  Complete the full course even if feeling better
  Never share antibiotics or take leftover antibiotics
  Report side effects to prescriber
  
WHO PRIORITY PATHOGENS (critical):
  Carbapenem-resistant Acinetobacter baumannii
  Carbapenem-resistant Pseudomonas aeruginosa
  Carbapenem-resistant Enterobacteriaceae (CRE)
  These are last-resort antibiotic resistant

CHAIN OF INFECTION: agent → reservoir → exit → transmission → entry → host
TRANSMISSION: contact | droplet (>5µm, <1m) | airborne (<5µm, >1m) | vector
PPE DONNING: gown → mask → goggles → gloves
PPE DOFFING: gloves → goggles → gown → mask (most contaminated first)
ISOLATION: contact (MRSA) | droplet (flu/COVID) | airborne (TB/measles — N95 + negative pressure)
AMR: natural selection of resistant bacteria | complete courses | no self-medication