ð Þ~exp {r 3 ð Þ. To progress further with analysing this system, I propose to approximate the process by assuming that infections within a household can be approximately described by a discrete generation Reed-Frost model, i.e. where the probability of not being infected in each generation is (Q n ) m where m individuals are infected in the previous generation and Q n u exp (2r n ). Q n is the escape probability of each infectious-susceptible pair of individuals considered in isolation. In the formalism proposed by Ludwig, this corresponds to using infectious rank as a surrogate for infectious generation [33] . Dynamics are recovered by assuming the times between generations are described by the standard generation time distribution w (t).