43 Decline in AmpC beta-lactamase-producing E. coli in a Dutch teaching hospital found a carriage rate of 3.2% of phenotypically confirmed AmpC-producing E.coli and 0.7% pAmpC producers based on PCR and WGS (Ulstad et al. 2016). In the Netherlands three studies on AmpC prevalence were performed in the community. A random sample of adult volunteers (n = 1033) by van Hoek et al. found an overall AmpC prevalence of 1.4%, consisting of 0.6% pAmpC and 0.8% cAmpC. Koningstein et al. screened faecal samples of day-care centre attending children and found an AmpC rectal carriage rate of 2.4%, with 1.2% blaCMY-2 producing E.coli and 1.1% cAmpC hyperproducers (Van Hoek et al. 2015; Koningstein et al. 2015). Finally, a study by Reuland et al., that screened adult volunteers in the region of Amsterdam found 1.3% carriage of pAmpC producing E. coli (E. Ascelijn Reuland et al. 2015). These results correspond with the prevalence rates in the present study for 2013 and 2014 for pAmpC and cAmpC. The three Dutch studies used pre-enrichment broths, but applied different screening tests. No studies have looked at trends over time in rectal carriage of AmpC. To our knowledge, this study is the first to show a declining trend of cAmpC within the North-Western European region. Based on the mentioned criteria in combination with AFLP, few cases of probable genetic clonality were detected. As not all isolated were subjected to strain typing a conclusion on epidemiological relationship cannot be made. Although we noticed heterogeneity of cAmpC alterations over the years, we cannot fully rule out the possibility of clustering of cAmpC isolates in the strains that were not subjected to AFLP during the first years. Future analysis is needed to clarify the situation of clonal spread and the possibility of horizontal spread of resistance genes. Trend analysis was adjusted for gender using logistic regression analysis. Data on other risk factors known for ESBL-E carriage, which might be applicable to AmpC carriage as well, like travel history or antibiotic use before admission were not available. A limitation of this PPS is the lack of evidence on sensitivity and specificity of screening agars used to detect AmpC producing isolates. No commercial AmpC specific screening agars are available. During the 4-year period, a change in our used screening agar was made to improve the sensitivity and specificity. The used MacConkey agar, containing cefotaxime 1 mg/L (Mediaproducts, Groningen, The Netherlands) was accepted to be sensitive for AmpC producing isolates, but not very specific, as other cephalosporin resistant Enterobacteriaceae (e.g. ESBL or K1-betalactamase producing isolates) were cultured as well. This could lead to overgrowth of isolates with other resistance mechanisms. To improve specificity, new AmpC agars were used, containing cefoxitin and cefotaxime as well as a combination of cefoxitin and ceftazidime. Retrospective screening of the 2013 isolates on the new screenings agar showed growth of all AmpC producing isolates. Unfortunately, we were not able to use the original rectal 3
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