all surfaces, even those with a deviating shape. Additionally, cotton swabs have higher recovery rates on wet surfaces, and have similar or better recovery rates when compared to other sampling methods (42, 53, 54). However, recovery rates of swabs remain low, for example for S. aureus in vitro recovery rates range between 22 and 58% (42, 43). This is mainly due to the difficulty in standardization of sampling (42). Finally, this sampling method provided us the opportunity to use selective broths. Because of this, we were able to detect MDRO that were present in low abundance. Second, the presence of dry biofilm could also be an important explanation for our low contamination rates, which are present on all types of surfaces (55). Even when no planktonic bacteria were identified on a surface, viable bacteria were identified in biofilms (56-58). Hu et al. showed that MDROs were found on ICU surfaces, even after terminal disinfection was performed (58). Besides the fact that the presence of dry biofilm decreases detection of bacteria, they also hamper cleaning and disinfection (59, 60). Almatroudi et al. showed that live S. aureus were present, even after the majority of biofilm was removed by sodium hypochlorite at 20,000 ppm (60). Parvin et al. showed that while a single wiping action was able to remove planktonic S. aureus, 50 wipes were necessary to remove biofilm (59). In our hospital, daily cleaning is performed with microfiber cloths, dampened with water, without a cleaning or disinfection solution. Disinfection is only performed when indicated. While cleaning is essential in keeping hospitals microbiologically safe and could help in preventing healthcare-associated infections, cleaning protocols vary widely and literature on evidence-based practices for hospital cleaning is scarce (61). However, Berendt et al. showed that swiping plastic surfaces with any type of moist wipes decreases the bioburden, and that saline wipes can be just as effective as disinfectant wipes when used appropriately (62). Additionally, Rutala et al. identified that sterile water was effective at removing more than 95% of the test bacteria (63). This supports our standard protocol of only cleaning with damp microfiber cloths. Based on the fact that sampling methods and the presence of dry biofilm will also lead to underestimation of environmental contamination rates in other countries and hospitals, we conclude that our cleaning protocol is an important contributor to the low contamination rates with MDRO (0.1% of surfaces) observed in the new building in the three years after relocating (Chapter 3.2). However, it is important to consider that our hospital is only three years old and thus that low contamination rates could be due to a relatively new building. However, how fast contamination rates increases and stabilize is not known. In Chapter 2.4, we compared the results of study samples, clinical samples, and environmental samples, to determine if we could show transmission from and to the hospital environment. We were unable to determine if the environment was the source of the acquired S. aureus. However, we identified patients with MSSA positive clinical samples who had an epidemiological link to the ward of a room positive for MSSA. From these patients, we identified 16 potential transmissions to or from the hospital environment. Four patients were admitted during sampling, and were consequently the most likely source of 4 193 Summarizing discussion
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