In epidemiology, force of infection (denoted
) is the rate at which susceptible individuals acquire an infectious disease.
[1] Because it takes account of susceptibility it can be used to compare the rate of transmission between different groups of the population for the same infectious disease, or even between different infectious diseases.
can be calculated for an infectious disease in an endemic state if homogeneous mixing of the population and a rectangular population distribution (such as that generally found in developed countries), rather than a pyramid, is assumed.
is the average age of infection.
is the average time spent in the susceptible group before becoming infected.
is that data on the average age of infection is very easily obtainable, even if not all cases of the disease are reported.