Exponential expansion of an infectious disease occurs when the rate of growth is proportional to the number of people currently infected. The mathematical formula for exponential growth is: [x_t = x_0(1+r)^t] In the case of Ebola, xt represents the total number of people infected, xâ‚’ represents the number of index cases at the starting point, r represents the rate of disease transmission (believed to be about 2 for Ebola, i.e.: each Ebola victim transmits the disease on average to 2 other people), and t (as an exponent) represents the time interval used for measurement (months). The formula reduces to xt...