Some microbes cause illness from a handful of cells. Others need millions. The ID₅₀ is the dose that infects half of the hosts exposed, and it is how virulence gets measured. Pick a pathogen, drag the dose, then change the host and watch the whole curve move.
24 exposed hostsred means infected
Dose given
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Dose needed
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Fall ill
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The dose–response curveupdates live
The median infectious dosepick a pathogen below
Exposure dose—
The host who is exposed
All six, this host and this dose
ID₅₀ is the dose that infects half of the hosts exposed. Its deadly cousin is the LD₅₀, the dose that kills half. A lower number means a more virulent organism.