How Many Microbes Does It Take to Make You Sick?

First it has to enter the body, bypassing natural barriers such as skin, mucus, cilia, and stomach acid..

Theyre similar ideas, but while infectious dose refers to how many organisms will lead to an infection, viral load is an active measurement of infection: the number of organisms that are replicating within the host..

A third way of trying to figure out infectious dose is to use observational studies, where researchers deduce the number from seeing how long it takes for an exposed person (especially in families or other close-contact settings) to become sick..

Researchers have suggested that pathogens requiring direct contact with host cells tended to be more effective, so their infectious doses were fairly low..

These studies suggest that one reason the virus is so easily transmissible is because it has a relatively low infectious dose, similar to other respiratory viruses such as RSV and common cold coronaviruses (and lower than the infectious dose of most strains of influenza virus)..

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