Transmission of respiratory tract infection

Airborne precautions

• Small particles (<5 microns) travel long distances and remain airborne
• Require standard infection control precautions and a FFP3
• Limited indications - multi-drug resistant TB, some viruses, RTI undergoing aerosol generating procedures

Droplet

• Larger particles (> 5 microns) fall to the floor within 2m
• Spread - direct contact of droplets with mucus membranes OR droplet → surface → contact spread
• Ideally patients should be kept in a single room

S. pneumoniae

Structure and virulence factors

• The capsule is the key virulence factor
  • Anti-phagocytic
  • Used in sero-typing
  • Basis for vaccination
  • Rough strains (avirulent)
• Other virulence factors:
  • Surface adhesins
  • Pneumolysin (cytotoxin)
  • sIgA protease
  • Teichoid acid
  • H2O2

Conducting airway defences

• Mucociliary escalator
• Cough
• AMPs
• Cellular and humoral immunity
• Infections occur when there are changes
  • Trauma/intubation of the airway
  • Abnormalities of defence e.g. ciliary escalator and others as occurs in COPD and CF
  • Virulent pathogen/ large incolulum

Cystic fibrosis