  Clusters of infected individuals are defined on data from health
laboratories, but this quantity has not been defined and characterized by
epidemy models on statistical physics. For a system of mobile agents we
simulate a model of infection without immunization and show that all the
moments of the cluster size distribution at the critical rate of infection are
characterized by only one exponent, which is the same exponent that determines
the behavior of the total number of infected agents. No giant cluster survives
independent on the magnitude of the rate of infection.
