External quality assessment (EQA) of Neisseria gonorrhoeae antimicrobial susceptibility testing in primary laboratories in Germany
Authors: Selb Regina , Jansen Klaus , Eckardt Matthias , Tamminga Thalea , Dudareva Sandra , Gassowski Martyna , Graeber Ingeborg , Guhl Eva , Heuer Dagmar , Buder Susanne ,   the GORENET EQA study group, Balau Veronika , Nagel Daniela , Berger Anja , Sing Andreas , Chapot Valerie , Steinmann Jörg , Fischer Heinrich , Kösel Siegfried , Dreyer Vanessa , Tonnemacher Ute , Groß Andreas , Hagedorn Hans Jochen , Hackel Tilo , Halfmann Alexander , Becker Sören , Hess Christina , Blümel Benjamin , Korten Simone , Sahly Hany , Laban Yulia , Friedrichs Claudia , Schmidt-Wieland Torsten , Oberdorfer Klaus , Pfüller Roland , Regnath Thomas , Woelke Corinna , Ruckert Carolin , Mertes Thomas , Knost-Streicher Carola , Krämer Sabine , Schüttert Inka , Skov Robert , Schwarz Roman , Streit-Schmid Doris , Walch Daniela , Mai Madeleine , Hunfeld Klaus-Peter , Wichelhaus Thomas A. , Wille Andreas , Muhl Carolin , Overhoff Judith 
Published: July 2020

Abstract
Background
Worldwide, an increase in antimicrobial resistance (AMR) of Neisseria gonorrhoeae has been observed. Until now, no protocol for an external quality assessment (EQA) has been available for Germany. The German gonococcal resistance network (GORENET) performed an EQA of primary laboratories in Germany in order to assess quality of antibiotic susceptibility testing, to gain information about laboratory procedures and to assess the impact of these procedures on test results.

Methods
Laboratories assessed drug susceptibility to cefixime, ceftriaxone, azithromycin, penicillin and ciprofloxacin for five N. gonorrhoeae strains, using their standard laboratory protocols. Minimal inhibitory concentrations (MICs) were compared to World Health Organisation (WHO) consensus results (or, if not available, reference laboratory results), while deviation by +/− one doubling dilution was accepted. Data on laboratory procedures were collected via a standardised questionnaire. Generalized linear models and conditional inference trees (CTREE) were used to assess relationships between laboratory procedures and testing outcomes.

Results
Twenty-one primary laboratories participated in the EQA in June 2018. 96% of ciprofloxacin MICs were reported within accepted deviations, as well as 88% for cefixime, 85% for ceftriaxone, 79% for penicillin and 70% for azithromycin. The use of interpretation standards and general laboratory procedures like agar base, incubation settings or the use of control strains strongly differed between laboratories. In statistical analysis, incubation time of cultures < 24 h was associated with correct measurements. Additionally, a 5% CO2 concentration was associated with correct results regarding azithromycin compared to 3%. CTREE analysis showed that incubation time, humidity and CO2 concentration had the greatest influence on the average deviation from consensus results.

Conclusions
In conclusion, we report the development of a protocol for N. gonorrhoeae antimicrobial susceptibility testing in Germany. While testing results were in accordance with the expected consensus results in 70–96%, depending on the antibiotic agent, laboratory methodology was heterogeneous and may significantly affect the testing quality. We therefore recommend the development of a standard operating procedure (SOP) for N. gonorrhoeae susceptibility testing in Germany.