  In this work, we study the critical behavior of an epidemic propagation model
that considers individuals that can develop drug resistance. In our lattice
model, each site can be found in one of four states: empty, healthy, normally
infected (not drug resistant) and strain infected (drug resistant) states. The
most relevant parameters in our model are related to the mortality, cure and
mutation rates. This model presents two distinct stationary active phases: a
phase with co-existing normal and drug resistant infected individuals and an
intermediate active phase with only drug resistant individuals. We employ a
finite-size scaling analysis to compute the critical points the critical
exponents ratio $\beta/\nu$ governing the phase-transitions between these
active states and the absorbing inactive state. Our results are consistent with
the hypothesis that these transitions belong to the directed percolation
universality class.
