Diekmann [OPJ90] defined the basic reproductive ratio R0, as the spectral radius (i.e the dominant
eigenvalue) of the next-generation matrix. In light of this, we shall in this section, formulate the nextgeneration matrix for a general epidemic model in which the population of individuals is separated into two sets of compartments namely: infected and uninfected. We assume that, of the n compartments,the first m compartments consist of infected individuals while the remaining m + 1; :::; n are assumed
to be made up of the uninfected individuals.