• Occurs worldwide:
    • Common in the developing world
    • Rare in the developed world due to vaccination programmes:
  • Most frequently encountered in densely populated regions in hot, damp climates with soil rich in organic matter
  • Temporal pattern – peaks in the summer or wet season
  • Mortality exceeds 50% in developing countries
  • Significantly lower with modern intensive care:
    • Mortality reported at 10-15%
    • Most fatalities in those that:
      • Unvaccinated
      • Aged >60 or <18