External quality assessment schemes in bacteriology support public health in Germany-results from 2006 to 2023

Abstract

External Quality Assessment schemes (EQAS) are mandatory to ensure quality standards in diagnostic methods and achieve laboratory accreditation. As host institution for two German culture-based bacteriology EQAS (RV-A and RV-B), we investigated the obtained data of 590 up to 720 surveys per year in RV-A and 2,151 up to 2,929 in RV-B from 2006 to 2023. As educational instruments, they function to review applied methodology and are valuable to check for systemic- or method-dependent failures in microbiology diagnostics or guidelines. Especially, containment of multi-resistant bacteria in times of rising antibiotic resistance is one major point to assure public health. The correct identification and reporting of these strains is therefore of high importance to achieve this goal. Moreover, correct antimicrobial susceptibility testing (AST) per se is important for selecting appropriate therapy, to restrict broad-spectrum antibiotics and minimize resistance development. The reports of participating laboratories displayed a high level of correct identification results in both schemes with mostly consistent failure rates around 2.2% (RV-A) and 3.9% (RV-B) on average. In contrast, results in AST revealed increasing failure rates upon modification of AST requirements concerning adherence to standards and subsequent bacterial species-specific evaluation. Stratification on these periods revealed in RV-A a moderate increase from 1.3% to 4.5%, while in RV-B failure rates reached 14% coming from 4.3% on average. Although not mandatory, subsequent AST evaluation and consistent reporting are areas of improvement to benefit public health.

Keywords: antimicrobial susceptibility testing (AST); bacteriology; external quality assessment; identification methods bacteriology; microbiology; public health.

FIGURE 1

Analysis of participants and passing rates in bacteriology EQAS RV-A and RV-B. (A) Number of participants in both EQA schemes from 2006 to 2023 for the respective annual dates. (B) Failure rates in RV-A (blue) and RV-B (red) EQAS at the respective dates with red arrows indicating time points of the described modifications in the EQAS. (C) Overall failure rates in RV-A and RV-B categorized for the periods between the aforementioned modifications in the EQAS. Depicted are mean ± SD for 12 (2006–2011), 18 (2012–2020), and 6 (2021–2023) data points in RV-A and 24 (2006–2011), 36 (2012–2020), and 12 (2021–2023) in RV-B.

FIGURE 2

Analysis of identification rates over time. (A) Failure rates in identification in RV-A and RV-B categorized in periods with regard to modifications in the EQAS. Dots represent respective overall failure rates per EQAS survey. (B) Identification rate for bacterial species being sent out at least three times from 2009 until 2023 in RV-B. Gram-negatives depicted in shades of red, gram-positives in shades of blue according to the legend in the graph, while the dotted line represents the regression line over all data points excluding rates for A. urinae. Regression analysis gave a slope of 0.049 (95% CI: 0.009–0.108). (C) Analysis of utilized identification methods for Enterobacterales in RV-A for the indicated time points. (D) Frequency of MALDI-TOF as identification method among RV-A (blue) and RV-B (red) participants.

FIGURE 3

Adherence to new taxonomy A Data display the frequency of bacterial species undergoing taxonomy changes being reported with the former name correlated to the time between publication of the new name and the respective EQAS round. The dotted line indicates categorization in more than 5 years since publication and equal or less for the respective data points. Significance was tested by a chi-square test. *** = p < 0.005.

FIGURE 4

Analysis of antimicrobial susceptibility testing (AST). (A) Failure rates in AST for RV-A and RV-B categorized in periods with regard to modifications in the EQAS. Depicted are mean ± SD for 6 (2009–2011), 18 (2012–2020), and 6 (2021–2023) data points in RV-A and 6 (2009–2011), 36 (2012–2020), and 6 (2021–2023) in RV-B. (B) Frequency of AST standard used by participants in RV-A from 2012 to 2023. Color schemes of the different standards according to the figure legend.

FIGURE 5

Reporting of urology guideline-recommended antibiotics in RV-B. Reporting frequencies of specific antibiotic substances for Escherichia coli normalized for ciprofloxacin rates as 100% in four individual RV-B rounds in 2021 and 2022. Substances are grouped into oral and parental antibiotics as well as antibiotics recommended by a German S3 guideline for uncomplicated urinary tract infections as first-line therapy.