Comparability of laboratory diagnosis and antimicrobial susceptibility testing of Neisseria gonorrhoeae from reference laboratories in Western Europe

Objectives: The aim of this study was to obtain information on the comparability of methods for the laboratory diagnosis of bacterial sexually transmitted infections (STIs) that contribute to the surveillance data in the European Union (EU) and Norway. Surveillance of bacterial STIs is important across Europe because of the movement of individuals between countries at a time when STI incidence appears to be increasing in many countries. Methods: Cross-sectional survey using a questionnaire, to provide information on laboratory methods for the diagnosis of gonorrhoea, and a panel of strains of Neisseria gonorrhoeae, to compare susceptibility testing, was circulated to laboratories in the EU and Norway. Results: The questionnaire revealed marked diversity in the methodologies used for the laboratory diagnosis of gonorrhoea across Europe. Fourteen laboratories participated in an exchange of gonococcal strains to assess the methodology in current use for susceptibility testing. The methods included disc diffusion and determination of the minimum inhibitory concentration (MIC) using agar dilution and/or Etest. There was no common method used, each centre varied from another by at least one procedure. Overall agreement using all methods was >70%, being highest for ceftriaxone and lowest for tetracycline. Disc diffusion gave the lowest agreement with the consensus compared with determination of MIC by either agar dilution or Etest. Conclusions: A variety of methods were used across the EU and Norway for the laboratory diagnosis and susceptibility testing and resulted in poor concordance between laboratories on the definition of resistant N. gonorrhoeae. This suggests that there is a need for greater standardization of methodology that provides surveillance data in the EU and Norway.