A basic principle in infectious disease epidemiology that expresses in a mathematical formula some important predictive variables influencing the course of epidemics. These variables relate the anticipated course of an infectious disease epidemic to the number of susceptible persons in the population, the number of current infectious cases, the incubation period or serial interval, which is the period between analogous phases of two successive waves of the epidemic, and the infection transmission parameter, a constant for each specific infectious disease. The relationship is expressed in a formula:
where Ct+1 is the number of new cases one serial interval in the future, Ct is the number of current cases, St is the number of susceptibles, and r is the infection transmission parameter.
Subjects: Public Health and Epidemiology.