  The diffusive epidemic process is a paradigmatic example of an absorbing
state phase transition in which healthy and infected individuals spread with
different diffusion constants. Using stochastic activity spreading simulations
in combination with finite-size scaling analyses we reveal two qualitatively
different processes that characterize the critical dynamics: subdiffusive
propagation of infection clusters and diffusive fluctuations in the healthy
population. This suggests the presence of a strong-coupling regime and sheds
new light on a longstanding debate about the theoretical classification of the
system.
