Infectious dose

Infectious dose is the number of viable pathogens or infectious particles required to establish infection in a host. It varies with the pathogen, route of exposure, and host susceptibility.

Dose–response relationship: A quantitative relationship between the amount of an agent received and the probability or severity of an effect. It describes how increasing pathogen exposure changes the chance of infection.
Infectious agent: A biological agent capable of causing infection, including viruses, bacteria, fungi, and parasites. Infectious dose counts viable agents capable of initiating infection.
Minimum infectious dose: The lowest dose observed or estimated to cause infection under defined conditions. It is often treated as a threshold, unlike probabilistic dose-response estimates.
Lethal dose: The amount of a substance or agent that causes death in a specified fraction of an exposed population. It measures mortality rather than the establishment of infection.
ID50: The dose that infects 50 percent of exposed hosts under specified conditions. It is a standard statistical measure of infectious dose.
Pathogen: A microorganism or other biological agent that can cause disease in a host. Pathogen identity helps determine how many agents can establish infection.
Microbial risk assessment: A structured evaluation of the likelihood and consequences of harm from microbial hazards. Risk assessments use dose-response information to estimate infection after exposure.
Toxic dose: The amount of a substance that produces harmful effects in an organism. Toxicity can occur without infection by a replicating pathogen.
Quantal dose–response model: A model relating dose to the fraction of individuals experiencing a binary outcome, such as infection. It estimates infection probability across a population with differing susceptibility.
Host susceptibility: The degree to which a host is vulnerable to infection or disease. Immune status and other host traits alter the dose needed for infection.

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