🦠microbiology review

Median infectious dose (ID50)

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Median infectious dose (ID50) is the amount of a pathogen required to infect 50% of a test population. It is used to quantify the virulence of a pathogen.

5 Must Know Facts For Your Next Test

  1. ID50 is a measure of pathogenicity and virulence.
  2. A lower ID50 value indicates a more virulent pathogen.
  3. ID50 can vary depending on the route of entry into the host.
  4. It is often determined through controlled laboratory experiments on animal models.
  5. Comparing ID50 values helps in assessing the relative risks posed by different pathogens.

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