Multidrug-resistant microorganisms A microorganism is defined as a multidrug-resistant microorganism (MDRO) when it is resistant to one or more classes of antimicrobial agents (1). MDRO are considered as an important threat to public health (2, 3). Examples of MDRO are extended-spectrum betalactamase-producing Enterobacterales (ESBL-E), carbapenemase-producing Enterobacterales (CPE), methicillin-resistant Staphylococcus aureus (MRSA), vancomycinresistant Enterococcus faecium (VRE) and carbapenemase-producing Pseudomonas aeruginosa (CP-PA). Among Enterobacterales, Escherichia coli, Klebsiella pneumoniae, and Citrobacter freundii are most frequently encountered. The worldwide increase in MDRO is causing increasing healthcare costs, morbidity, and mortality in patients (3, 4). The prevalence of MDRO differs per country and per type of MDRO, ranging from less than one percent to more than 50% of isolates. Within the Netherlands, the prevalence of MDRO is generally low, although it differs per type of microorganism. The prevalence of MRSA nasal carriage upon admission to the hospital ranged between 0.03-0.17% between 2010 and 2017 (5), while the prevalence of ESBL-E intestinal carriage in the Netherlands between 2011 and 2016 ranged between 4.5% and 8.6% (6-8). MDRO are a common cause of healthcare-associated infections (HAI), which are infections caused by pathogens acquired by patients during their stay in a healthcare institution (9). HAI can be caused by microorganisms from an endogenous or exogenous source. Endogenous sources are body sites, including skin; exogenous sources are external sources, such as the hospital environment, its surfaces, or health care workers. This thesis is focused on endogenous sources by screening patients to identify microorganisms present upon admission to the hospital, and on exogenous sources, specifically the hospital innate environment and the transmission from the environment to the patient and vice versa. Relocation of the Erasmus MC The Erasmus MC University Medical Center (Erasmus MC) in Rotterdam, the Netherlands, is the largest academic hospital of the Netherlands. It includes the adult clinic (“Dijkzigt”), the Sophia Children’s hospital, the Erasmus MC Cancer Institute and the Faculty of Medicine and Health sciences of the Erasmus University Rotterdam. From 1961 until May 18, 2018, the hospital was located in the Dijkzigt hospital building, while the Erasmus MC Cancer Institute was on a location named “Daniel den Hoed”. In 2009, the Erasmus MC started the construction of a new hospital building, directly next to the old hospital building (Figure 2) as replacement of the Dijkzigt hospital and the Erasmus MC Cancer Institute. At the beginning of the design process, it became clear that the relocation would be accompanied by a reduction in the number of beds due to expected changes in the organization of health care, resulting in less admission days. To optimize microbial safety and to make the most use out of the available number of beds, the decision 1 9 General introduction
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