  The finite temperature phase transition of strongly interacting matter is
studied within a nonlocal chiral quark model of the NJL type coupled to a
Polyakov loop. In contrast to previous investigations which were restricted to
the mean-field approximation, mesonic correlations are included by evaluating
the quark-antiquark ring sum. For physical pion masses, we find that the pions
dominate the pressure below the phase transition, whereas above T_c the
pressure is well described by the mean-field approximation result. For large
pion masses, as realized in lattice simulations, the meson effects are
suppressed.
