  A hybrid network--deterministic model for simulation of multiresistant
pathogen spread in a healthcare system is presented. The model accounts for two
paths of pathogen transmission between the healthcare facilities:
inter-hospital patient transfers (direct transfers) and readmission of
colonized patients (indirect transfers). In the latter case, the patients may
be readmitted to the same facility or to a different one. Intra-hospital
pathogen transmission is governed by a SIS model expressed by a system of
ordinary differential equations.
  Using a network model created for a Lower Saxony region (Germany), we showed
that the proposed model reproduces the basic properties of
healthcare-associated pathogen spread. Moreover, it shows the important
contribution of the readmission of colonized patients on the prevalence of
individual hospitals as well as of overall healthcare system: it can increase
the overall prevalence by the factor of 4 as compared to inter-hospital
transfers only. The final prevalence in individual healthcare facilities was
shown to depend on average length of stay by a non-linear concave function.
  Finally, we demonstrated that the network parameters of the model may be
derived from administrative admission/discharge records. In particular, they
are sufficient to obtain inter-hospital transfer probabilities, and to express
the patients' transfer as a Markov process.
