Effect of Differences in the CLSI and EUCAST Criteria on the Interpretation of Enterobacteriaceae Sensitivity to Carbapenems

Relevance: The two systems for determining the susceptibility of bacteria to antimicrobial drugs, CLSI and EUCAST, are recommended for use in the global system of epidemiological surveillance of antimicrobial resistance of the World Health Organization. However, they differ in the methodology of setting an antimicrobial susceptibility testing, threshold values of cut-off points, as well as interpretation of results. The true significance of methodological differences between these systems for global microbiological monitoring is unclear.

The aim of the study was to evaluate the influence of differences in the cut-off points of CLSI and EUCAST on the interpretation of antimicrobial sensitivity of microorganisms to carbapenems in Saint Petersburg.

Design: screening and comparative study.

Materials and methods. Sensitivity to Meropenem was studied in Escherichia coli (n=2956), as well as Klebsiella pneumoniae (n=1189) for the period of 2011–2013 and 2016–2019, and interpreted according to the threshold values of the two guidelines (2020). Results. The weighted Kappa showed good agreement between the EUCAST vs CLSI standards for both E.coli (0.58; 95% CI 0.55–0.61) and K.pneumoniae (0.77; 0.73–0.81). Mcnemar's Chi-square test revealed differences between the two standards in assessing sensitivity to Meropenem of E.coli which were 5.31% (95% CI 5.06–5.31%, P<0.0001), and of K.pneumoniae — 3.95% (95% CI 3.36–3.95%, P<0.0001).

Conclusion. The reliability of determining sensitivity bacteria to anti-microbial drugs has a significant impact on their rational use and the results of microbiological monitoring. The first priority is to develop national standards that take regional characteristics into account.

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