environmental contamination. Two patients were discharged before environmental sampling was performed, but were still the most likely source. One patient was admitted 61 days after environmental sampling, indicating potential transmission from the environment to the patient. However, due to the time frame this does not seem likely. Nine patients were admitted to the ward, but no to the contaminated room. This could indicate transmission on the ward. Overall, we conclude that the patient admitted to the room is the most likely source of environmental contamination with S. aureus as measured during stay of that particular patient. The study of Chen et al. determined transfers of MDRO from patients to the hospital environment and vice versa (38). They identified that in one third of cases, the patient was the source of environmental contamination, that in one third the environment was the source for the strain acquired by the patient, and that in the final one third, the direction could not be determined. Interestingly, the two transfers with MRSA were either from the patient to the environment or not determined. However, their results highlight that, even though we observed that the patient was the likely source, this does not diminish the importance of the hospital environment in transmission of MDRO. Besides determining the contamination with MDRO and S. aureus, we also determined the total bioburden of surfaces the number of colony forming units (CFU) in Chapter 3.2. We observed fluctuating levels of the CFU counts over the three year follow up, with lower levels during the COVID-19 pandemic. This could be related to the enhanced cleaning and disinfection performed during this period. In literature, suggestions have been made for cutoff values for CFU counts on hand contact surfaces in healthcare facilities. Dancer et al. suggested a cutoff value of <5 CFU/cm2, while Griffith et al. suggested a cutoff value of <2.5 CFU/cm2 (64, 65). Due to our method, we were unable to determine if the cutoff value of <5 CFU/cm2 was exceeded, but the cutoff value of <2.5 CFU/cm2 was exceeded, especially in the bathroom. While CFU counts provide a good indication of the total bacterial load of a surface, they do not provide information about what bacteria are present. When we focus on MDRO, other studies have not identified a correlation between CFU counts and the presence of MDRO (66, 67). In general, nosocomial pathogens are present in low concentrations (68). Consequently, we conclude that CFU counts only provide limited information about the environmental contamination and should not be used on its own when determining environmental contamination. While CFU counts provide a good indication of the overall bioburden and could be used to determine cleaning efficacy, when the aim of environmental sampling is to determine environmental colonization with specific target bacteria, other sample methods (e.g., targeted screening) are more effective. 194 Chapter 4
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