IntroductionHospital-acquired infections (HAIs) are of immense clinical, epidemiological and ethical importance for healthcare systems worldwide (ECDC, 2012; Jarvis, 1996). Many of these infections are caused by multidrug resistant organisms (MDROs), of which the Methicillin Staphylococcus aureus (MRSA) is the most common one. High economic burden of HAIs can be referred to increased co-morbidity and mortality resulting in prolonged hospital lengths of stay as the main cost driver (Cosgrove et al., 2005; de Kraker et al., 2011; Wenzel, 1995; Zimlichman et al., 2013). Multidrug resistant pathogens complicate treatment procedures considerably and lead to significantly longer hospital lengths of stay (de Kraker et al., 2011). In 2008, the European Centre for Disease Prevention and Control (ECDC) estimated 171,200 nosocomial MRSA infections, 5,400 attributable excess deaths and more than 1 million excess days of hospitalization per year which goes along with 380 million Euros excess in-hospital costs per year (ECDC, 2012).To combat the spread of multiresistant bacteria, hospitals are confronted with additional costs due to hygienic measures, e.g. admission screening, and precaution isolation of patients (Herr et al., 2003; Hubner et al., 2014; Wilcox, 2004). A few studies demonstrate a positive cost-benefit ratio of theses hygiene preventive measures (Farbman et al., 2013). Nevertheless, these additional costs are only partly accounted in hospital financing systems (Vegni et al., 2004). The financial impact of nosocomial infections on reimbursements under prospective Diagnosis Related Group (DRG) conditions is already long controversially debated (DeWitt, 1987). MDROs present a new challenge not least because of their growing clinical importance. However, there are hardly any scientific studies conducting the impact of MDRO-infections on the DRG-system.1. Encoding of multiresistant organism in the German DRG-systemThe German DRG System was introduced in 2003 and contains a diagnosed-regarded, lump-sum classification system. Each DRG corresponds with an economically-comparable case-group specified by the clinical diagnosis, diagnostic and therapeutic interventions as well as patients' comorbidities and subsequent complications. Key elements of a DRG are the mean length of stay with a lower and an upper limit, which indicates discount or surcharge rates, and the cost weight. There are ICD-10-based secondary diagnoses for the coding of comorbidities as well as OPS-codes for special performed procedures.Over the past years several adjustments of the DRG system have been made, whereby also hospital acquired infections with multidrug-resistant pathogens should be better reflected. Originally, these costs were not included in DRGs and therefore not covered (Vegni et al., 2004). A positive MDRO-status can be indicated by the secondary diagnosis U80.0! or U81.0! in combination with Z22.3 Z29.0. (colonization) or B.95.6 (infection). For the isolation of MDRO-positive patients, the OPS 8-987! should be used if minimum requirements are met (documented additional expenses of at least 2 hours per day, e.g. for special experienced staff, screening, isolation and decolonization measures, over at least 7 days). Since 2007 specific complex DRG for MDRO-associated diseases exist for encoding.The encoding of MDOR-relevant parameters may have an impact on the hospital revenue, as the following example shows (Table 1).The example of Table 1 shows a difference of 575.09 Euro in favour of encoding of MDRO-parameters. This revenue growth is relatively low compared to the additional cost due to hygienic prevention measures and other therapeutic procedures (Herr et al., 2003; Hubner et al., 2014). Furthermore, encoding of MDRO-parameters does not always result in a revenue relevance, sometime it can be even revenue reductive (de Zeeuw and Baberg, 2009). If the required conditions for OPS 8-987! can not be achieved, no MDRO-relevant encoding is possible at all. …