environment, which can be explained by the fact that they are easily available in a healthcare setting, easy in use, and associated costs are low (41). Results of environmental sampling can be reported as presence/absence, as the abundance in which a target microorganism is present, or the total bacterial load of a surface can be presented as the number of colony forming units (CFU). Currently, there are no guidelines on how to perform environmental sampling (41, 42). In this thesis (chapter 3.1), we aim to determine what the current environmental sampling practices within Europe are, and if there is a consensus on how and when to sample the hospital environment. Transmission from the hospital environment to patients Transmission from the hospital environment to patients can take place through either direct contact with the contaminated surfaces, or indirect contact, e.g., via the hands of healthcare workers (HCW). The crucial role of the hospital environment in outbreaks was highlighted by a study of Gastmeier et al., in which they identified the source of 1,561 published outbreaks (43). No source was identified for 37.1% of outbreaks. For the outbreaks where a source was identified, the source was an index patient (40.3%), equipment and devices (21.1%), personnel (15.8%), and the environment (19.8%) (43). The role of the environment in transmission is also highlighted by the study of Wu et al. (16). They determined that, when the previous roommate was colonized or infected with a MDRO, the current room occupant has a higher chance on becoming colonized or infected with that MDRO (16). Since there is no direct contact with a previous roommate, this transmission is most likely through the environment, either via direct or indirect contact. Staphylococcus aureus is a well-known commensal, and an important cause of both community- and hospital-acquired bacteremia and other severe infections (44, 45). While the majority of nosocomial S. aureus infections (~80%) are endogenous, patients with exogenous infections, although not well understood, tend to have longer hospitalizations after bacteremia and a higher risk of mortality (46, 47). Furthermore, exogenous infections are, due to their origin, theoretically preventable. Consequently, it is important to strive for 100% prevention of spread of S. aureus. For this we have to understand the mode and factors of transmission to be able to install adequate IPC measures. Since S. aureus can survive on surfaces from hours up to several months, the hospital environment can be an important source of transmission (36, 48). Transmission of S. aureus from the hospital environment or hands of HCW to patients have been shown (49, 50). However, the dynamics of S. aureus in patients, in the hospital environment and between the hospital environment and patients are relatively unknown, specifically in non-outbreak settings. In this thesis (chapter 2.4), we aim to determine colonization and acquisition rates of patients with S. aureus and environmental contamination with S. aureus, and subsequently 16 Chapter 1
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