- 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