Statistics of infections with diversity in the pathogenicity

The statistics of outbreaks in a model for the propagation of meningococcal disease is analyzed, taking into account the possibility that the population is fragmented into weakly connected patches. It is shown that, depending on the size of the sample studied, the ration between the variance and the average of infected cases can vary from unity (Poisson statistics) to ε−1, where ε is the normalized infection rate.