The basic reproductive rate or the intrinsic rate of reproduction is the number of secondary infections caused by the introduction of a single infectious case into a completely susceptible population. This metric is useful because it helps determine whether or not an infectious disease will spread through a population.

The basic reproductive rate is affected by several factors including: the duration of infectivity of affected patients, how infectious the organism is and the number of susceptible people in the population that the affected patients are in contact with.

If this number is greater than one, on the average, a disease will spread within that population. If this number is less than one, on the average, a disease will eventually fade from a population.

This statistic is often referred to by the name R₀. It was originally used by George MacDonald in 1952, who constructed population models of the spread of malaria.

See also

• Theoretical ecology.
• Branching process.