and consequently might reduce costs associated with sampling. Additionally, standardization of environmental sampling could help to make national and international results more comparable. Since environmental sampling is mainly performed during (ongoing) outbreaks, information on bacterial contamination of the hospital environment during non-outbreak settings is rare. However, several studies have been conducted in non-outbreak settings, identifying that up to 55% of rooms had at least one surface contaminated with a MDRO (38, 46-48). In Chapter 3.2, we report the results of three-years of environmental sampling (41). In the old hospital building, we identified the presence of MDRO on 3.3% of all sampled surfaces, and in the new hospital building on 0.1% of all sampled surfaces. This contamination rate is very low compared to the other studies. An important factor is the difference in prevalence rates of MDRO between the countries. The Netherlands has a very low prevalence of MDRO, while the majority of studies were performed in the United States, which has a higher MDRO prevalence (49-51). Besides contamination with MDRO, we also have determined the contamination rates with S. aureus in Chapter 2.4. It is important to note that, while the low prevalence of MDRO might explain the low contamination rates, the prevalence of MSSA carriage is not lower in the Netherlands and should thus not impact environmental contamination rates (10, 11). The observed environmental contamination rates were low, with 3.0% of surfaces positive for methicillin-susceptible S. aureus (MSSA), in the old building, and 2.8% of surfaces in the new hospital building, and no methicillin-resistant S. aureus (MRSA) identified in both buildings. A study in the UK identified MSSA/MRSA on 5.316.1% of the sampled surfaces (52). We identified that when multiple locations in one patient room were present at the same moment, these strains belonged to the same spatype and most likely had the same source. Locations that were MSSA positive over time differed in spa-type. From this, we conclude that environmental contamination with S. aureus is temporarily. It is known that S. aureus is able to survive up to seven months on surfaces (36). Consequently, it is likely that the temporary contamination is not due to the S. aureus, but due to external factors, such as our such as our sampling protocol, the presence of dry biofilm, and our cleaning activities. It is likely that these factors also contributed to the low contamination rates found with MDRO. First, our sampling protocol; all sampling methods come with disadvantages and none have a recovery rate of 100%. Consequently, results of environmental sampling will per definition show an underestimation of the true environmental contamination. Therefore, it is key to choose a sampling method best suited to the specific situation. As we sampled different types and different shaped surfaces, both wet and dry locations, and we were interested in multiple target microorganisms, we decided to use cotton swabs. These swabs were premoistened with PBS before sampling a standardized surface of 100 cm2 (with the exception locations with a deviating shape, such as the doorknob, the shower drain, and the top and bottom of the sink plug, for which the entire surface was sampled). To standardize sampling, we first swabbed horizontally, then vertically, and finally diagonally, while rotating the swab. Because we chose this sampling method, we could easily sample 192 Chapter 4
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