Some microbes make you sick from a handful of cells; others need millions. That number — the ID₅₀, the dose that infects half of exposed hosts — is how we measure virulence. Pick a pathogen, then drag the exposure dose.
Exposed hosts
Pick a pathogen to begin
The median infectious dosetap a pathogen below
Exposure dose—
ID₅₀
dose
110³10⁶10⁹
Read the dose–responseThe ID₅₀ is a fixed property of the pathogen. Slide the dose marker left of a microbe's ID₅₀ and most hosts stay well; slide it right and most fall ill. A low ID₅₀ = high virulence.
ID₅₀ = the dose that infects half of exposed hosts. Its lethal cousin is the LD₅₀ (dose that kills half). Lower value → more virulent organism.