  Motivated by recent lattice QCD studies, we explore the effects of
interactions on strangeness fluctuations in strongly interacting matter at
finite temperature. We focus on S-wave $K\pi$ scattering and discuss the role
of the $K_0^*(800)$ and $K^*(1430)$ resonances. The interaction contribution is
obtained within the S-matrix formulation of thermodynamics, using the empirical
$K\pi$ phase shifts as input. We find that the simplified treatment of the
interactions in this channel, employed in the hadron resonance gas approach,
leads to an overestimate of the strangeness fluctuations. Thus, our calculation
indicates that broad resonances must be treated with caution, when modeling QCD
thermodynamics in the hadronic phase.
