Infectious dose

Infectious dose (ID) is the amount of pathogen (measured in number of microorganisms) required to cause an infection in the host.

Usually it varies according to the pathogenic agent and the consumer's age and overall health.

Infectious doses for some known microorganisms

 * Escherichia coli : very large (106 - 108 of organisms)
 * Salmonella : quite large in order to definitely establish infection (e.g. > 105 of organisms) but infection may also be established by lower numbers (e.g. 10s of organisms).
 * Cholera : relatively large (104 - 106 of organisms)
 * Bacillus anthracis : relatively large (104 spores)
 * Campylobacter jejuni: low (500 organisms)
 * Francisella tularensis: very low (10-50 organisms)
 * Shigella : very low (10s of organisms)
 * C.parvum : very low (10 to 30 oocysts)
 * Escherichia coli O157:H7 : very low ( < 10 organisms)
 * Entamoeba coli : extremely low (from 1 cyst)

The likelihood of infection in all cases is also linked to the immune status of the individual (immunocompromised individuals may become infected more readily).